什么是并发控制中的2PL

悠悠 2022-07-28 01:11 124阅读 0赞

In this blog I will describe the concurrency control methods implemented in database management systems, and the differences between them. I will also explain about what locking technique is used in [CUBRID RDBMS][], about locking modes and their compatibility, and finally, the deadlocks and the solution for them.

## Overview ##

When multiple transactions, which change the data, are executed simultaneously, it is required to control the order of processing these transactions to satisfy the [ACID][] (Atomicity, Consistency, Integrity, Durability) property of the database. *Executing multiple transactions simultaneously should lead to the same result as executing each transaction independently*, in other words, one transaction should not be affected by another transaction.

If different data is changed for each transaction, no interference between transactions is made, so there is no issue. However, if the same data is simultaneously changed by multiple transactions, the order of processing each transaction should be controlled.

## Types of Concurrency Control ##

For example, the **T1 transaction** changes the **A record** from *1* to *2* and then changes the **B record**, the **T2 transaction** can simultaneously change the **A record**, too. Let's assume that the **T2 transaction** changes the **A record** from *2* to *4* by adding **+2**. If two transactions are successfully terminated, there is no issue. But it is important that all transactions can be rolled back. If the **T1 transaction** is rolled back, the value of the **A record**should be returned to *1*, i.e. the value *before* the **T1 transaction** was executed. This is to satisfy the ACID property of the database. However, the **T2 transaction** has already changed the **A record** value to *3*. So, it is impossible to return the **A record** to *1* regardless of the situation. In this case, there can be two options.

1.  [Two-phase locking (2PL)][Two-phase locking _2PL]  
      
    The first one is when the **T2 transaction** tries to change the **A record**, it knows that the **T1 transaction** has already changed the **A record** and waits until the **T1 transaction** is completed because the **T2 transaction** cannot know whether the **T1 transaction** will be committed or rolled back. This method is called **Two-phase locking (2PL)**.
2.  [Multi-version concurrency control (MVCC)][Multi-version concurrency control _MVCC]  
      
    The other one is to allow each of them, **T1** and **T2 transactions**, to have their own changed versions. Even when the **T1 transaction** has changed the **A record** from *1* to *2*, the **T1 transaction** leaves the original value*1* as it is and writes that the ***T1 transaction version*** of the **A record** is **2**. Then, the following **T2 transaction**changes the **A record** from *1* to *3*, **not** from *2* to *4*, and writes that the ***T2 transaction version*** of the **A record** is **3**.  
      
    When the **T1 transaction** is rolled back, it does not matter if the **2**, ***the T1 transaction version***, is not applied to the **A record**. After that, if the **T2 transaction** is committed, the **3**, ***the T2 transaction version***, will be applied to the **A record**. If the **T1 transaction** is committed prior to the **T2 transaction**, the **A record**is changed to 2, and then to 3 at the time of committing the **T2 transaction**. The final database status is identical to the status of executing each transaction independently, without any impact on other transactions. Therefore, it satisfies the ACID property. This method is called **Multi-version concurrency control (MVCC)**.

CUBRID has implemented 2PL method as well as DB2 and SQL Server, while Oracle, InnoDB and PostgreSQL have implemented MVCC.

## Two-phase locking in CUBRID ##

The 2PL adopted by CUBRID uses locks to ensure the consistency between transactions that change the identical data. As the "lock" literally means, **the locking is executed through two phases**:

1.  expanding phase (acquiring)
2.  shrinking phase (releasing)

More accurately, all transactions should acquire lock for the data to be accessed and the acquired locks are released only when the transaction is terminated. After a transaction has acquired the lock for a certain data (regardless of the lock type, `S_LOCK` for read, stands for *Shared Lock*, or `X_LOCK` for write, stands for *Exclusive Lock*), when another transaction tries to acquire a new lock for the data, the new lock is allowed or pended depending on the [lock compatibility rule][]. Therefore, success or failure of the prior transaction does not have impact on the following transactions, so the data consistency is maintained.

## Lock Manager in CUBRID ##

Thus, the **key point of 2PL**, adopted by CUBRID, is that **the lock must be processed through two phases**: *expanding phase* and *shrinking phase*. Then, **\[Figure 1\]** *release all locks, acquired while executing a transaction, only after the transaction ends (commit or rollback)*.

![two-phase-lock.png][]

**Figure 1: Two-Phase Locking.**

2PL concurrency control method naturally controls access to the identical data from transactions by making all transactions observe the 2PL protocol. The following **Figure 2** below shows an example of three transactions using 2PL: **Transaction 1** executes **B=B+A** operation, **Transaction 2** executes **C=A+B** operation, and **Transaction 3** executes **Print C** operation. Since all three transactions are accessing the data A, B and C, the concurrency control is required. In this case, each transaction is executed according to the 2PL protocol so that there is no data conflict.

![concurrency-control-using-2PL.png][]

**Figure 2: Concurrency Control by using 2PL.**

### Lock modes ###

To understand the concurrency control of multiple transactions more deeply, let's discuss about [lock modes][],**lock conversion** and [transaction isolation level][]. In the above figure, you can see that `S-lock`, *Shared Lock*, for**A** was first acquired by **Transaction 1**, but it is also acquired by **Transaction 2**, too. On the contrary, the transaction which requested `X-lock` is blocked until `S-lock` is released. In this matter, a [variety of lock modes][lock modes]are used to minimize conflicts by lockers. Major types of locks utilized in DBMSs are.

*  **Shared (S) Lock**: Used for read operation. It is generally set on the target record when `SELECT` statement is executed. It blocks a transaction from changing data which was already read by other transactions.
 *  **Exclusive (X) Lock**: Used for write-operations such as `INSERT`, `UPDATE`, `DELETE`. It blocks one data from being changed by multiple transactions.
 *  **Update (U) Lock**: Used to define that the target resource will be changed. It is used to minimize deadlock which may occur when multiple transactions are executing both read and write.
 *  **Intent Shared (IS) Lock**: Set on the upper resource (e.g. tables) to set the `S-lock` on some lower resources (e.g. records or pages). It is to prevent other transactions from setting `X-lock` on the upper resource. Intent lock will soon be described.
 *  **Intent Exclusive (IX) Lock**: Set on the upper resource to set `X-lock` on some lower resources.
 *  **Shared with Intent Exclusive (SIX) Lock**: Set on the upper resource to set `S-lock` and `X-lock` on some lower resources.

#### LOCK MODE COMPATIBILITY ####

Among the lock modes above, **intent locks** are used to *improve the transaction concurrency* and to *prevent deadlock* between the upper resources and the lower resources. For example, when **Transaction A** tries to read**Record R** on **Table T**, it sets `IS_LOCK` on **Table T** before setting `S_LOCK` on **Record R**. Then, **Transaction B** is prevented from setting `X_LOCK` on **Table T** to change the structure of **Table T**. If **Transaction A** has not set`IS_LOCK` on **Table T**, **Transaction B** would change the structure of **Table T**. Then, **Transaction A** would perform a wrong read operation. This way **Transaction B** has no need to check all records in **Table T** to check whether there is any lock set by other transactions for setting `X_LOCK` on **Table T**. The following lock mode compatibility table will clearly show the effect of intent locks:

<table style="width:726px; border:1px solid rgb(122,160,205); border-collapse:collapse; border-spacing:0px; margin:0px auto; color:rgb(0,0,0); font-family:Calibri,'Times New Roman',Times,serif; font-size:16px; background-color:rgb(244,247,250)">  
 <strong>Table 1: The lock mode compatibility table of CUBRID.</strong>  
 <thead style="color:rgb(255,255,255); background:rgb(78,129,189)"> 
  <tr style="border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(255,255,255)"> 
   <th colspan="2" style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> &nbsp;</th> 
   <th colspan="9" style="padding:3px; font-weight:normal; border-right-style:none"> Current Lock Mode</th> 
  </tr> 
  <tr style="border-bottom-style:none"> 
   <th style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> NULL</th> 
   <th style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> IS</th> 
   <th style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> NS</th> 
   <th style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> S</th> 
   <th style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> IX</th> 
   <th style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> SIX</th> 
   <th style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> U</th> 
   <th style="padding:3px; font-weight:normal; border-right-width:1px; border-right-style:solid; border-right-color:rgb(255,255,255)"> NX</th> 
   <th style="padding:3px; font-weight:normal; border-right-style:none">X</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr style="background:rgb(255,255,255)"> 
   <th style="padding:3px">Newly-requested Lock Mode</th> 
   <th style="padding:3px">NULL</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-style:none">True</td> 
  </tr> 
  <tr style="border-top-width:1px; border-top-style:solid; border-top-color:rgb(122,160,205); border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(122,160,205); background:rgb(211,223,237)"> 
   <th style="padding:3px">IS</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-style:none">False</td> 
  </tr> 
  <tr style="background:rgb(255,255,255)"> 
   <th style="padding:3px">NS</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-style:none">False</td> 
  </tr> 
  <tr style="border-top-width:1px; border-top-style:solid; border-top-color:rgb(122,160,205); border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(122,160,205); background:rgb(211,223,237)"> 
   <th style="padding:3px">S</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-style:none">False</td> 
  </tr> 
  <tr style="background:rgb(255,255,255)"> 
   <th style="padding:3px">IX</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-style:none">False</td> 
  </tr> 
  <tr style="border-top-width:1px; border-top-style:solid; border-top-color:rgb(122,160,205); border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(122,160,205); background:rgb(211,223,237)"> 
   <th style="padding:3px">SIX</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-style:none">False</td> 
  </tr> 
  <tr style="background:rgb(255,255,255)"> 
   <th style="padding:3px">U</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-style:none">False</td> 
  </tr> 
  <tr style="border-top-width:1px; border-top-style:solid; border-top-color:rgb(122,160,205); border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(122,160,205); background:rgb(211,223,237)"> 
   <th style="padding:3px">NX</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> N/A</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-style:none">False</td> 
  </tr> 
  <tr style="background:rgb(255,255,255)"> 
   <th style="padding:3px">X</th> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> True</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-width:1px; border-right-style:solid; border-right-color:rgb(204,204,204)"> False</td> 
   <td style="padding:3px; border-right-style:none">False</td> 
  </tr> 
 </tbody> 
</table>

From the lock mode compatibility table, you can see that `X_LOCK` cannot be set on a table if `IS_LOCK` is set on the table. And only `IS_LOCK` can be compatible with `SIX_LOCK`. This means that `SIX_LOCK` intends to set`S_LOCK` and `X_LOCK` on the record and it will not allow any lock but `IS_LOCK` for `S_LOCK` on other non-conflicting records. From the table, you can see that `IX_LOCK` and `IX_LOCK` can be compatible with each other.`IX_LOCK` intends to set `X_LOCK` for some records. So, the compatibility is available. If there are two transactions that try to change an identical record, `IX_LOCK` for the table is allowed. However, there is no problem in concurrency control since only the transaction that has acquired `X_LOCK` for the record first can change the record (`X_LOCK` and `X_LOCK` are not compatible).

The lock mode compatibility table is expressed as a global variable `lock_Comp[][]` in the ***lock\_table.c*** file in[CUBRID source code][]. Among CUBRID sources, most codes related to lock modes are implemented in***lock\_manager.c*** file. To set lock on a data object, the `lock_object()` function is used which receives three parameters: the **OID of an object** where the lock mode will be set, **the OID of the class** where the object belongs, and **the desired lock mode**. In the source code of the function, you can see that the function is executed in several ways based on the **target of the lock mode**, the **lock mode for an instance object** or **for a class object**.

> **Take note of this**: in CUBRID, a class object is also an object. Keep it in mind that a class object has an [OID][] and all class objects are the instances of a root class, so it uses ROOTOID, the OID of the root object, as its class OID.

From the code, you can see that the required intent lock is set on a class object when a lock mode is required for an instance object. And there is **a concept of lock waiting time** in the lock mode request. To retrieve the lock timeout value set on the current transaction, the `logtb_find_wait_secs()` function is called. CUBRID supports the `SET TRANSACTION LOCK TIMEOUT` SQL command and the `setLockTimeout()` method in JDBC. The command is to specify the **lock timeout** of the current transaction. Lock waiting time means the time for a transaction, which has made a request for lock mode, to wait when a lock mode is set on an object by a transaction and the requested lock is not compatible with the already-set lock mode. As you have seen before, the 2PL concurrency control method does not allow lock from other transactions until the existing lock is released. For the following two reasons, lock timeout should be set by a transaction:

1.  When a user does not want to wait too long because of the lock mode.
2.  To lower the frequency of deadlock.

### Deadlocks ###

A deadlock occurs when two or more transactions request resources locked by each of them, so all transactions cannot be progressed. **Figure 8** below shows an example of a deadlock.

![transaction\_deadlock.png][transaction_deadlock.png]

**Figure 2: Transaction Deadlock.**

First, **Transaction 1** executes `UPDATE participant SET gold=10 WHERE host_year=2004 AND nation_code=’KOR’` statement and sets `X_LOCK` on the `‘KOR’` record. Transaction 2 sets `X_LOCK` on the `‘JPN’` record. Transaction 3 sets `X_LOCK` on the `‘CHN’` record.

After that, **Transaction 1** requests `X_LOCK` on the `‘JPN’` record for executing `UPDATE` for that record. However, the `‘JPN’` record is already locked with `X_LOCK` by **Transaction 2**. So, **Transaction 1** should wait until **Transaction 2** ends. Based on the 2PL protocol, the `X_LOCK` is released when the transaction ends. **Transaction 2** requests `X_LOCK` on the `‘CHN’`record and waits for **Transaction 3**. Finally, **Transaction 3** waits for **Transaction 1** to acquire the `'KOR'` record of **Transaction 1** as it has `X_LOCK` on the `‘CHN’` record. As a result,**Transaction 1** waits for **Transaction 2** to end, **Transaction 2** waits for **Transaction 3** to end, and **Transaction 3** waits for **Transaction 1** to end. So, no transaction can be progressed. This is called a **deadlock**.

Most DBMSs which use the 2PL method, including CUBRID, use the **deadlock detection method** to solve the deadlock problem. It periodically checks whether the cycle illustrated in the above figure occurs by drawing a**Lock Wait Graph** for the transactions being executed.

In CUBRID, the thread for detecting deadlock checks the **Lock Wait Graph** every second. When a deadlock is detected, one transaction among the transactions is randomly selected and aborted by force. This is called**unilateral abort**. When a transaction is selected as a victim to be sacrificed to solve the deadlock and unilaterally aborted, the corresponding SQL statement returns an error code. The error message is "**The transaction has timed out due to deadlock while waiting for `X_LOCK` for an object. It waited until User 2 ended.**” When an error is returned and the application aborts the transaction, the locks of the transaction are released and other transactions can be continuously processed.

To see how the deadlock is detected, see the `lock_detect_local_deadlock()` function in the source code. This function is called with the intervals (in seconds) specified by the `PRM_LK_RUN_DEADLOCK_INTERVAL` variable (the`deadlock_detection_interval_in_secs` parameter in [cubrid.conf][] file) on the background thread which executes`thread_deadlock_detect_thread()`.

Even if a deadlock does not occur, when the execution time of a transaction is too long, other transactions should wait for too long as well. For a certain application, it is wiser to give up rather than wait. In particular, when a web server has called DB tasks and the wait time is too long, all threads of the web server are used to process the DB, so they cannot be used to process external HTTP requests any more, causing service failures. Therefore, for a web application, the threads should be returned without waiting an unlimited amount of time for DB processing even if an error occurs. Two methods are used for that:

1.  One is **lock timeout** supported by CUBRID.
2.  The other is **query cancel**. JDBC is defined with an API which can cancel the SQL statement being executed.

The key data structure of the lock manager is defined in the ***lock\_manager.c*** file.

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    <div style="border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(85,216,57)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em 0px 1em!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important">
      34 
    </div> 
    <div style="border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(85,216,57)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em 0px 1em!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important">
      35 
    </div> 
    <div style="border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(85,216,57)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em 0px 1em!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important">
      36 
    </div> 
    <div style="border-width:0px 3px 0px 0px!important; border-right-style:solid!important; border-right-color:rgb(85,216,57)!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em 0px 1em!important; position:static!important; right:auto!important; text-align:right!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important">
      37 
    </div> </td> 
   <td style="border-right-style:none; width:690px; padding:0px!important; border-top-width:0px!important; border-bottom-width:0px!important; border-left-width:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> 
    <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:7px 0px!important; position:relative!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; background:none!important"> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">typedef</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> struct</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> lk_entry LK_ENTRY;</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">struct</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> lk_entry</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">{ </code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">#if defined(SERVER_MODE)</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">struct</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> lk_res *res_head;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* back to resource entry&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">THREAD_ENTRY *thrd_entry;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* thread entry pointer&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">int</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> tran_index;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* transaction table index&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LOCK granted_mode;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* granted lock mode&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LOCK blocked_mode;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* blocked lock mode&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">int</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> count;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* number of lock requests&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">struct</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> lk_entry *next;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* next entry&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">struct</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> lk_entry *tran_next;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* list of locks that trans. holds&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">struct</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> lk_entry *class_entry;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* ptr. to class lk_entry&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LK_ACQUISITION_HISTORY *history;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* lock acquisition history&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LK_ACQUISITION_HISTORY *recent;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* last node of history list&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">int</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> ngranules;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* number of finer granules&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">int</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> mlk_count;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* number of instant lock requests&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">unsigned&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">char</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> scanid_bitset[1];&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* PRM_LK_MAX_SCANID_BIT/8];&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">#else&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /* not SERVER_MODE */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">int</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> dummy;</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; color:gray!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">#endif&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; /* not SERVER_MODE */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">};</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important">
       &nbsp; 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">typedef</code> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> struct</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> lk_res LK_RES;</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; font-weight:bold!important; color:rgb(85,216,57)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">struct</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important"> lk_res</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">{ </code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">MUTEX_T res_mutex;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* resource mutex */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LOCK_RESOURCE_TYPE type;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* type of resource: class,instance */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">OID oid;</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">OID class_oid;</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LOCK total_holders_mode;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* total mode of the holders */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LOCK total_waiters_mode;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* total mode of the waiters */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LK_ENTRY *holder;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* lock holder list */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LK_ENTRY *waiter;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* lock waiter list */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LK_ENTRY *non2pl;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* non2pl list */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="color:inherit; white-space:nowrap; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">LK_RES *hash_next;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="white-space:nowrap; color:rgb(143,144,138)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">/* for hash chain */</code> 
     </div> 
     <div style="border:0px!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; margin:0px!important; outline:0px!important; overflow:visible!important; padding:0px 0.5em!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-size:1em!important; min-height:auto!important; white-space:pre!important; background:transparent!important"> 
      <code style="white-space:nowrap; color:rgb(255,255,255)!important; overflow:visible!important; padding:0px!important; border:0px!important; margin:0px!important; font-size:1em!important; bottom:auto!important; float:none!important; height:auto!important; left:auto!important; line-height:1.1em!important; outline:0px!important; position:static!important; right:auto!important; top:auto!important; vertical-align:baseline!important; width:auto!important; font-family:Consolas,'Bitstream Vera Sans Mono','Courier New',Courier,monospace!important; min-height:auto!important; background:none!important">};</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

From the file, the `lk_Gl` global variable of `LK_GLOBAL_DATA` type is the core. The `LK_ENTRY` structure stands for the lock itself. For example, when the **Transaction T1** has requested a lock, one `LK_ENTRY` is created. `LK_RES` is a structure that shows to which resource the lock belongs. In CUBRID, all resources are objects (instance objects and class objects), so they are shaped as OIDs. In the `LK_RES` structure, you can see the list of holders with `LK_ENTRY` type and the list of waiters. The list of holders is a list of transactions that hold the lock for the resource now. For example, when **Transaction T1** and **Transaction T2** have acquired `S_LOCK` for the data record with OID1, `LK_ENTRY` that corresponds to the `S_LOCK` of **T1** and **T2** will be registered in the list of holders. When **Transaction T3** requests `X_LOCK` on the OID1 record, **T3** should wait because of the existing`S_LOCK`. So, the `LK_ENTRY` corresponding to `X_LOCK` of T3 will be registered to the list of waiters. Which lock is held by which transaction is maintained in the `tran_lock_table` variable which has the `LK_TRAN_LOCK` structure as a table.

The **Wait For Graph** for detecting a deadlock is expressed as `TWFG_node` and `TWFG_edge` of the `LK_WFG_NODE`structure and the `LK_WFG_EDGE` structure. The `lock_detect_local_deadlock()` function creates a **Wait For Graph**and detects whether there is a cycle on the graph. When a cycle is detected, the `lock_select_deadlock_victim()`function selects a victim transaction to be sacrificed for solving the deadlock. For reference, transactions are continuously executed while a **Wait For Graph** is drawn up and checked, the information of the ended transaction is removed from the graph. The victim transaction is selected based on the following criteria:

*  If a transaction is not a holder, it cannot be a victim.
 *  When a transaction is in the commit phase or the rollback phase, it cannot be selected as a victim.
 *  Select a transaction of which lock timeout is not set to -1 (unlimited waiting) first.
 *  Select the latest transaction rather than the older one. (The transaction ID is an incremental number. A transaction with smaller transaction number is the older one.)

## Conclusion ##

This concludes the talk about Two-Phase Locking in CUBRID. I briefly covered the types of concurrency control, the difference between 2PL and MVCC, about what locking technique is used in CUBRID RDBMS, about locking modes and their compatibility, and finally, the deadlocks and the solution for them.

In this article I have mentioned about OID (Object Identifiers) which are used to identify instance objects as well as class objects. In the next article I will continue this talk and explain what Object, Class, and OID are.

[CUBRID RDBMS]: http://www.cubrid.org/
[ACID]: http://en.wikipedia.org/wiki/ACID
[Two-phase locking _2PL]: http://en.wikipedia.org/wiki/Two-phase_locking
[Multi-version concurrency control _MVCC]: http://en.wikipedia.org/wiki/Multiversion_concurrency_control
[lock compatibility rule]: http://www.cubrid.org/transaction_and_lock
[two-phase-lock.png]: /images/20220727/f27f3e5d0ea043f8ad70be19802b7185.png
[concurrency-control-using-2PL.png]: /images/20220727/72b31868c9a7434c9a33b0eaadbdea6d.png
[lock modes]: http://www.cubrid.org/manual/90/en/Lock%20Mode%20Types%20And%20Compatibility
[transaction isolation level]: http://www.cubrid.org/manual/90/en/Transaction%20Isolation%20Level-Overview
[CUBRID source code]: http://www.cubrid.org/wiki_tutorials/entry/cubrid-source-code
[OID]: http://www.cubrid.org/questions/235437
[transaction_deadlock.png]: /images/20220727/1cc1a77929284b90a2f4fbf9b5c33798.png
[cubrid.conf]: http://www.cubrid.org/manual/90/en/cubrid.conf