Tomcat源码分析（三）------ 可携带状态的线程池

摘自http://blog.csdn.net/cutesource/article/details/5081916

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：

[java] view
plaincopy

/**

* 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：

[java] view
plaincopy

/**

* 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：

[java] view
plaincopy

/**

* 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();

}

}