jvm的jstack定位线程状态问题

谁借莪１个温暖的怀抱￠ 2022-12-29 01:45 199阅读 0赞

#### 背景 ####

1.  如果存在线程之间相互等待，造成大量线程处于blocked状态，应该如何定位问题？

#### 过程 ####

*  **测试代码**

public class JVM_Thread_Problem01 { 
        private static Object obj = new Object();
    
        public static void main(String[] args) throws InterruptedException { 
            new Thread(new Runnable() { 
                @Override
                public void run() { 
                    synchronized (obj) { 
                        try { 
                            Thread.sleep(Long.parseLong("111111"));
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                        System.out.println("0");
                    }
                }
            }, "Thread-0").start();
    
            new Thread(new Runnable() { 
                @Override
                public void run() { 
                    synchronized (obj) { 
                        try { 
                            Thread.sleep(Long.parseLong("111111"));
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                        System.out.println("1");
                    }
                }
            }, "Thread-1").start();
    
            new Thread(new Runnable() { 
                @Override
                public void run() { 
                    synchronized (obj) { 
                        try { 
                            Thread.sleep(Long.parseLong("111111"));
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                        System.out.println("2");
                    }
                }
            }, "Thread-2").start();
    
            new Thread(new Runnable() { 
                @Override
                public void run() { 
                    synchronized (obj) { 
                        try { 
                            Thread.sleep(Long.parseLong("111111"));
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                        System.out.println("3");
                    }
                }
            }, "Thread-3").start();
        }
        
    }

*  **jstack pid （线程栈信息）**

2020-12-18 12:43:15
    Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.181-b13 mixed mode):
    
    "DestroyJavaVM" #15 prio=5 os_prio=0 tid=0x00000000033c2800 nid=0x2330 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Thread-3" #14 prio=5 os_prio=0 tid=0x0000000020cac000 nid=0x234c waiting for monitor entry [0x0000000021a4f000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at jvm.JVM_Thread_Problem01$4.run(JVM_Thread_Problem01.java:54)
            - waiting to lock <0x0000000757d248c8> (a java.lang.Object)
            at java.lang.Thread.run(Thread.java:748)
    
    "Thread-2" #13 prio=5 os_prio=0 tid=0x0000000020c4b000 nid=0x3214 waiting for monitor entry [0x000000002194f000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at jvm.JVM_Thread_Problem01$3.run(JVM_Thread_Problem01.java:40)
            - waiting to lock <0x0000000757d248c8> (a java.lang.Object)
            at java.lang.Thread.run(Thread.java:748)
    
    "Thread-1" #12 prio=5 os_prio=0 tid=0x0000000020c28800 nid=0x268c waiting on condition [0x000000002184e000]
       java.lang.Thread.State: TIMED_WAITING (sleeping)
            at java.lang.Thread.sleep(Native Method)
            at jvm.JVM_Thread_Problem01$2.run(JVM_Thread_Problem01.java:26)
            - locked <0x0000000757d248c8> (a java.lang.Object)
            at java.lang.Thread.run(Thread.java:748)
    
    "Thread-0" #11 prio=5 os_prio=0 tid=0x0000000020c24000 nid=0x39c0 waiting for monitor entry [0x000000002174f000]
       java.lang.Thread.State: BLOCKED (on object monitor)
            at jvm.JVM_Thread_Problem01$1.run(JVM_Thread_Problem01.java:12)
            - waiting to lock <0x0000000757d248c8> (a java.lang.Object)
            at java.lang.Thread.run(Thread.java:748)
    
    "Service Thread" #10 daemon prio=9 os_prio=0 tid=0x0000000020b83000 nid=0x3658 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C1 CompilerThread2" #9 daemon prio=9 os_prio=2 tid=0x0000000020ac6000 nid=0x3338 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread1" #8 daemon prio=9 os_prio=2 tid=0x0000000020a9f800 nid=0x18b8 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "C2 CompilerThread0" #7 daemon prio=9 os_prio=2 tid=0x0000000020a77800 nid=0x2558 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Monitor Ctrl-Break" #6 daemon prio=5 os_prio=0 tid=0x0000000020a9c800 nid=0xf44 runnable [0x000000002114e000]
       java.lang.Thread.State: RUNNABLE
            at java.net.SocketInputStream.socketRead0(Native Method)
            at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
            at java.net.SocketInputStream.read(SocketInputStream.java:171)
            at java.net.SocketInputStream.read(SocketInputStream.java:141)
            at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
            at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
            at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
            - locked <0x0000000757e79580> (a java.io.InputStreamReader)
            at java.io.InputStreamReader.read(InputStreamReader.java:184)
            at java.io.BufferedReader.fill(BufferedReader.java:161)
            at java.io.BufferedReader.readLine(BufferedReader.java:324)
            - locked <0x0000000757e79580> (a java.io.InputStreamReader)
            at java.io.BufferedReader.readLine(BufferedReader.java:389)
            at com.intellij.rt.execution.application.AppMainV2$1.run(AppMainV2.java:61)
    
    "Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000020293800 nid=0x18a4 waiting on condition [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001eeb4800 nid=0x2540 runnable [0x0000000000000000]
       java.lang.Thread.State: RUNNABLE
    
    "Finalizer" #3 daemon prio=8 os_prio=1 tid=0x00000000034bd800 nid=0xe38 in Object.wait() [0x00000000201ef000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x0000000757988ed0> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
            - locked <0x0000000757988ed0> (a java.lang.ref.ReferenceQueue$Lock)
            at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
            at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)
    
    "Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x00000000034b8000 nid=0x1ac4 in Object.wait() [0x00000000200ef000]
       java.lang.Thread.State: WAITING (on object monitor)
            at java.lang.Object.wait(Native Method)
            - waiting on <0x0000000757986bf8> (a java.lang.ref.Reference$Lock)
            at java.lang.Object.wait(Object.java:502)
            at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
            - locked <0x0000000757986bf8> (a java.lang.ref.Reference$Lock)
            at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
    
    "VM Thread" os_prio=2 tid=0x000000001ee67800 nid=0x3890 runnable
    
    "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00000000033de000 nid=0x5c0 runnable
    
    "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00000000033df800 nid=0xf9c runnable
    
    "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00000000033e1000 nid=0x3660 runnable
    
    "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00000000033e2800 nid=0x3154 runnable
    
    "VM Periodic Task Thread" os_prio=2 tid=0x0000000020c1a800 nid=0x3874 waiting on condition
    
    JNI global references: 12

*  **如上可以观察到的核心信息**

1.  waiting to lock <0x0000000757d248c8> (a java.lang.Object)， 可以看见多个线程都等待去上锁这个对象。
2.  JVM\_Thread\_Problem01.java:54， 可以定位到代码的具体某行，在排查错误的时候，非常有用。
3.  **waiting for monitor entry** \[0x000000002174f000\]， synchronized 上锁的时候，使用：monitor entry
4.  java.lang.Thread.State: **BLOCKED** (on object monitor)

*  **分析**

1.  因为某个线程，占用了资源，导致其他线程被阻塞住了。
2.  需要定位到，占用资源的线程，究竟，是程序中那段业务逻辑代码。一般是通过线程名称进行定位的。
3.  定位到了具体的代码后，就需要仔细阅读一下代码了。
4.  只能分析代码业务逻辑过程，才有可能找到问题原因。看见这些堆栈信息，也仅仅是定位问题而已，远没有到解决问题。

#### 小结 ####

*  如果出现了问题，内心只想能够很快解决问题，则会让自己心态受到一定影响。解决问题的过程一定是：定位问题，分析问题，解决问题。
 *  **定位问题**。定位问题的依据是什么？肯定是大量的**有意义的有效的资料信息**。比如堆栈信息，比如其他堆文件信息。
 *  **分析问题**。对代码和业务场景的理解，力求**找到问题的原因**。
 *  **解决问题**。找不到问题原因，永远解决不了问题。