jenkins源码分析 —— 接受主节点的远程请求（三）

客官°小女子只卖身不卖艺 2022-05-24 00:48 188阅读 0赞

本系列(参考[远程执行shell源码分析][shell])主节点是通过ssh方式连接(launch slave agents on unix machines via ssh)slave节点  
而在启动slave节点时会启动一个ReaderThread线程来接受主节点请求

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzODczNDMx_size_16_color_FFFFFF_t_70][]

### 启动ReaderThread ###

启动slave节点入口为：通过ssh-slaves项目的SSHLauncher类来启动slave

**public** **synchronized** void launch(**final** SlaveComputer computer, **final** TaskListener listener) **throws** InterruptedException \{   
  ...  
    openConnection(listener);  
    verifyNoHeaderJunk(listener);  
    reportEnvironment(listener);  
    String java = resolveJava(computer, listener);  
    String workingDirectory = getWorkingDirectory(computer);  
    copySlaveJar(listener, workingDirectory);  
  
    startSlave(computer, listener, java, workingDirectory);  
  ...  
\}

通过startSlave方法启动slave进程

**private** void startSlave(SlaveComputer computer, **final** TaskListener listener, String java, String workingDirectory) **throws** IOException \{   
...  
 computer.setChannel(session.getStdout(), session.getStdin(), listener.getLogger(), **null**);  
...  
\}

通过computer.setChannel调用jenkins-core项目SlaveComputer类的setChannel方法

**public** void setChannel(InputStream in, OutputStream out, OutputStream launchLog, Channel.Listener listener) **throws** IOException, InterruptedException \{   
    ChannelBuilder cb = **new** ChannelBuilder(nodeName,threadPoolForRemoting)  
       .withMode(Channel.Mode.NEGOTIATE)  
       .withHeaderStream(launchLog);  
  
   **for** (ChannelConfigurator cc : ChannelConfigurator.all()) \{   
        cc.onChannelBuilding(cb,**this**);  
   \}  
  
    Channel channel = cb.build(in,out);  
    setChannel(channel,launchLog,listener);  
\}

再通过Channel channel = cb.build(in,out)进入到remting项目ChannelBuilder类的build方法

**public** Channel build(InputStream is, OutputStream os) **throws** IOException \{   
       **return** **new** Channel(**this**,negotiate(is,os));  
   \}

通过negotiate(is,os)方法得到ChunkedCommandTransport对象

跳转到remoting项目Channel类的构造方法

**protected** Channel(ChannelBuilder settings, CommandTransport transport) **throws** IOException \{   
   ...  
    transport.setup(**this**, **new** CommandReceiver() \{   
       **public** void handle(Command cmd) \{   
            updateLastHeard();  
           **if** (logger.isLoggable(Level.FINE))  
                logger.fine("Received " \+ cmd);  
           **try** \{   
                cmd.execute(Channel.this);  
           \} **catch** (Throwable t) \{   
                logger.log(Level.SEVERE, "Failed to execute command " \+ cmd \+ " (channel " \+ Channel.this.name \+ ")", t);  
                logger.log(Level.SEVERE, "This command is created here", cmd.createdAt);  
           \}  
       \}  
  
       **public** void terminate(IOException e) \{   
            Channel.this.terminate(e);  
       \}  
   \});  
\}

Channel(ChannelBuilder settings, CommandTransport transport)构造方法接受ChunkedCommandTransport对象，由于  
ChunkedCommandTransport 继承——>> AbstractSynchronousByteArrayCommandTransport 继承——>> SynchronousCommandTransport 继承——>> CommandTransport

transport.setup调用SynchronousCommandTransport类的setup方法来启动一个ReaderThread线程

**public** void setup(Channel channel, CommandReceiver receiver) \{   
   **this**.channel = channel;  
   **new** ReaderThread(receiver).start();  
\}

### 读取对象 ###

通过上面的ReaderThread.start()方法启动一个线程，ReaderThread为SynchronousCommandTransport类的内部类，在run()方法中，通过cmd = read()读取对象

**private** **final** **class** **ReaderThread** **extends** Thread \{   
   **private** int commandsReceived = 0;  
   **private** int commandsExecuted = 0;  
   **private** **final** CommandReceiver receiver;  
  
   **public** ReaderThread(CommandReceiver receiver) \{   
       **super**("Channel reader thread: "\+channel.getName());  
           **this**.receiver = receiver;  
       \}  
  
       @Override  
       **public** void run() \{   
       **final** String name =channel.getName();  
       **try** \{   
           **while**(!channel.isInClosed()) \{   
                Command cmd = **null**;  
               **try** \{   
                    cmd = read();  
               \} **catch** (EOFException e) \{   
                    IOException ioe = **new** IOException("Unexpected termination of the channel");  
                    ioe.initCause(e);  
                   **throw** ioe;  
               \} **catch** (ClassNotFoundException e) \{   
                    LOGGER.log(Level.SEVERE, "Unable to read a command (channel " \+ name \+ ")",e);  
                   **continue**;  
               \} **finally** \{   
                    commandsReceived\++;  
               \}  
  
                receiver.handle(cmd);  
                commandsExecuted\++;  
           \}  
            closeRead();  
       \}  
       ...  
   \}  
\}

### 创建command对象，即UserRequest ###

通过上面的read()方法，调用remoting项目的AbstractSynchronousByteArrayCommandTransport的read方法创建一个command对象，即UserRequest([发送远程请求（二）][Link 1]最终发送的UserRequest)

**public** Command read() **throws** IOException, ClassNotFoundException \{   
   **return** Command.readFrom(channel,**new** ObjectInputStreamEx(  
           **new** ByteArrayInputStream(readBlock(channel)),  
            channel.baseClassLoader));  
\}

### 执行UserRequest ###

通过ReaderThread的run()方法里的receiver.handle(cmd)回调上面Channel类的构造方法里面的handle方法，而传入handle方法的cmd参数即通过上面read()得到的UserRequest

**protected** Channel(ChannelBuilder settings, CommandTransport transport) **throws** IOException \{   
...  
**public** void handle(Command cmd) \{   
    updateLastHeard();  
   **if** (logger.isLoggable(Level.FINE))  
        logger.fine("Received " \+ cmd);  
   **try** \{   
        cmd.execute(Channel.this);  
   \} **catch** (Throwable t) \{   
        logger.log(Level.SEVERE, "Failed to execute command " \+ cmd \+ " (channel " \+ Channel.this.name \+ ")", t);  
        logger.log(Level.SEVERE, "This command is created here", cmd.createdAt);  
   \}  
\}  
...  
\}

通过cmd.execute(Channel.this)来执行UserRequest

先是通过UserRequest的父类Request(继承Command)来执行execute()方法

**protected** **final** void execute(**final** Channel channel) \{   
    channel.executingCalls.put(id,**this**);  
    future = channel.executor.submit(**new** Runnable() \{   
  
       **private** int startIoId;  
  
       **private** int calcLastIoId() \{   
           int endIoId = channel.lastIoId();  
           **if** (startIoId==endIoId) **return** 0;  
           **return** endIoId;  
       \}  
  
       **public** void run() \{   
            String oldThreadName = Thread.currentThread().getName();  
            Thread.currentThread().setName(oldThreadName\+" for "\+channel.getName());  
           **try** \{   
                Command rsp;  
                CURRENT.set(Request.this);  
                startIoId = channel.lastIoId();  
               **try** \{   
                   // make sure any I/O preceding this has completed  
                   channel.pipeWriter.get(lastIoId).get();  
  
                    RSP r = Request.this.perform(channel);  
                   // normal completion  
                   rsp = **new** Response<RSP,EXC>(id,calcLastIoId(),r);  
            ...  
                   **synchronized** (channel) \{ // expand the synchronization block of the send() method to a check  
                       **if**(!channel.isOutClosed())  
                            channel.send(rsp);  
                   \}  
            ...  
       \}  
   \});  
\}

### 创建Runnable并提交到Executor ###

通过channel.executor.submit(new Runnable()\{...\})创建一个Runnable并通过submit提交到executor

然后通过Request.this.perform(channel)调用remoting项目UserRequest类的perform()方法

**protected** UserResponse<RSP,EXC> perform(Channel channel) **throws** EXC \{   
   **try** \{   
        ClassLoader cl = channel.importedClassLoaders.get(classLoaderProxy);  
  
        RSP r = **null**;  
        Channel oldc = Channel.setCurrent(channel);  
       **try** \{   
            Object o;  
           **try** \{   
                o = deserialize(channel,request,cl);  
       ...  
\}

### 创建Response ###

通过new Response<RSP,EXC>(id,calcLastIoId(),r)创建Response对象

### 发送Response ###

最终通过channel.send(rsp)把Response对象发送给主节点

[shell]: https://blog.csdn.net/qq_33873431/article/details/80348675
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMzODczNDMx_size_16_color_FFFFFF_t_70]: /images/20220524/6e446c0986224f8c94ba3093550e7f67.png
[Link 1]: http://www.lilihongblog.com/Blog/jenkins+Sending+Remote+Request