jenkins源码分析 —— 发送远程请求（二）

本文解析jenkins主节点向从节点发送远程请求过程的源码

job执行shell命令入口

入口位于jenkins-core项目下的CommandInterpreter类

public boolean perform (AbstractBuild <?,?> build , Launcher launcher , TaskListener listener ) throws InterruptedException {
...
 r = join (launcher . launch (). cmds (buildCommandLine (script )). envs (envVars ). stdout (listener ). pwd (ws ). start ());
...
}

通过上面的start方法启动一个新的进程

跳转到jenkins-core项目下的launcher类

public Proc start () throws IOException {
     return launch ( this );
}

然后调用launcher类的内部类RemoteLauncher的launch方法

public Proc launch (ProcStarter ps ) throws IOException {
    ...
    return new ProcImpl (getChannel (). call ( new RemoteLaunchCallable (ps . commands , ps . masks , ps . envs , in , ps . reverseStdin , out , ps . reverseStdout , err , ps . reverseStderr , ps . quiet , workDir , listener )));
    ...
}

通过Channel.call()发送远程请求

通过getChannel().call()调用remoting项目(即从节点的slave.jar)的Channel类的call方法

public <V ,T extends Throwable > V call (Callable <V ,T > callable ) throws IOException , T , InterruptedException {
            ...
            request = new UserRequest <V , T >( this , callable );
            UserResponse <V ,T > r = request . call ( this );
            return r . retrieve ( this , UserRequest . getClassLoader (callable ));
            ...
}

然后通过new UserRequest<V, T>(this, callable)方法来序列化callable(传入的是实现callable接口的RemoteLaunchCallable)并创建字节数组

通过new UserReques初始化UserRequest

位于remoting项目UserRequest类的构造方法

    public UserRequest (Channel local , Callable <?,EXC > c ) throws IOException {
        exports = local . startExportRecording ();
        try {
            request = serialize (c ,local );
        } finally {
            exports . stopRecording ();
        }

        this . toString = c . toString ();
        ClassLoader cl = getClassLoader (c );
        classLoaderProxy = RemoteClassLoader . export (cl ,local );
    }

1.通过serialize方法序列化RemoteLaunchCallable并创建字节数组

    private byte [] _serialize (Object o , final Channel channel ) throws IOException {
        Channel old = Channel . setCurrent (channel );
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream ();
            ObjectOutputStream oos ;
            if (channel . remoteCapability . supportsMultiClassLoaderRPC ())
                oos = new MultiClassLoaderSerializer . Output (channel ,baos );
            else
                oos = new ObjectOutputStream (baos );

            oos . writeObject (o );
            return baos . toByteArray ();
        } finally {
            Channel . setCurrent (old );
        }
    }

2. 创建一个ClassLoader代理

ClassLoader cl = getClassLoader (c );
classLoaderProxy = RemoteClassLoader . export (cl ,local );

3. 回到getChannel().call()方法，发送UserRequest到slave节点

UserResponse <V ,T > r = request . call ( this );
return r . retrieve ( this , UserRequest . getClassLoader (callable ));

通过request.call(this)调用remoting项目的Request类的call方法来发送UserRequest

     //Sends this request to a remote system, and blocks until we receives a response.
     public final RSP call (Channel channel ) throws EXC , InterruptedException , IOException {
        ...          
        // Channel.send() locks channel, and there are other call sequences
        // (  like Channel.terminate()->Request.abort()->Request.onCompleted()  )
        // that locks channel -> request, so lock objects in the same order
        synchronized (channel ) {
            synchronized ( this ) {
                response = null ;

                channel . pendingCalls . put (id , this );
                channel . send ( this );
            }
        }
        ...
    }

通过channel.send(this)方法，channel把UserRequest对象写入输出流

然后等待response响应