Tomcat源码分析（三）------ 可携带状态的线程池 (转)

最近想实现一个可携带状态的线程池，具体需求就是池中的线程被用来处理某种信息，而此信息可视为线程所依赖的外部状态。如果用简单的线程池来实现，线程初始化时就得赋予某些信息，使得线程无法被再次利用。在看老版Tomcat的源码时，找到了答案，其实现思路主要是利用了线程的等待和唤起，HttpProcessor的实现正好基于此思路，时序图如下所示：



初始化HttpProcessor线程时，没法赋予所需的Socket对象，因为如果在初始化阶段就赋予Socket会导致此线程没法回收用来处理其他Socket。因此，在HttpProcessor的run阶段，先把线程给wait住，具体在await方法里体现，代码如下所示：

/** 
* Await a newly assigned Socket from our Connector, or <code>null</code> 
* if we are supposed to shut down. 
*/ 
private synchronized Socket await() {  
 
    // Wait for the Connector to provide a new Socket  
    while (!available) {  
        try {  
            wait();  
        } catch (InterruptedException e) {  
        }  
    }  
 
    // Notify the Connector that we have received this Socket  
    Socket socket = this.socket;  
    available = false;  
    notifyAll();  
 
    if ((debug >= 1) && (socket != null))  
        log("  The incoming request has been awaited");  
 
    return (socket);  
 
} 
/**
* Await a newly assigned Socket from our Connector, or <code>null</code>
* if we are supposed to shut down.
*/
private synchronized Socket await() {

    // Wait for the Connector to provide a new Socket
    while (!available) {
        try {
            wait();
        } catch (InterruptedException e) {
        }
    }

    // Notify the Connector that we have received this Socket
    Socket socket = this.socket;
    available = false;
    notifyAll();

    if ((debug >= 1) && (socket != null))
        log("  The incoming request has been awaited");

    return (socket);

}

当HttpConnector调用HttpProcessor.assign(socket)方法时，会给此线程赋予Socket对象，并唤起此线程，使其继续执行，assign方法的源码如下所示：

/** 
* Process an incoming TCP/IP connection on the specified socket.  Any 
* exception that occurs during processing must be logged and swallowed. 
* <b>NOTE</b>:  This method is called from our Connector's thread.  We 
* must assign it to our own thread so that multiple simultaneous 
* requests can be handled. 
* 
* @param socket TCP socket to process 
*/ 
synchronized void assign(Socket socket) {  
 
    // Wait for the Processor to get the previous Socket  
    while (available) {  
        try {  
            wait();  
        } catch (InterruptedException e) {  
        }  
    }  
 
    // Store the newly available Socket and notify our thread  
    this.socket = socket;  
    available = true;  
    notifyAll();  
 
    if ((debug >= 1) && (socket != null))  
        log(" An incoming request is being assigned");  
 
} 
/**
* Process an incoming TCP/IP connection on the specified socket.  Any
* exception that occurs during processing must be logged and swallowed.
* <b>NOTE</b>:  This method is called from our Connector's thread.  We
* must assign it to our own thread so that multiple simultaneous
* requests can be handled.
*
* @param socket TCP socket to process
*/
synchronized void assign(Socket socket) {

    // Wait for the Processor to get the previous Socket
    while (available) {
        try {
            wait();
        } catch (InterruptedException e) {
        }
    }

    // Store the newly available Socket and notify our thread
    this.socket = socket;
    available = true;
    notifyAll();

    if ((debug >= 1) && (socket != null))
        log(" An incoming request is being assigned");

}

线程被唤起和赋予socket对象后，继续执行核心的process方法，HttpProcessor.run的完整源码如下所示：

/** 
* The background thread that listens for incoming TCP/IP connections and 
* hands them off to an appropriate processor. 
*/ 
public void run() {  
 
    // Process requests until we receive a shutdown signal  
    while (!stopped) {  
 
        // Wait for the next socket to be assigned  
        Socket socket = await();  
        if (socket == null)  
            continue;  
 
        // Process the request from this socket  
        try {  
            process(socket);  
        } catch (Throwable t) {  
            log("process.invoke", t);  
        }  
 
        // Finish up this request  
        connector.recycle(this);  
 
    }  
 
    // Tell threadStop() we have shut ourselves down successfully  
    synchronized (threadSync) {  
        threadSync.notifyAll();  
    }  
 
} 



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