Tomcat源码分析（三）------ 可携带状态的线程池

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：

/**
*AwaitanewlyassignedSocketfromourConnector,or<code>null</code>
*ifwearesupposedtoshutdown.
*/
privatesynchronizedSocketawait(){

//WaitfortheConnectortoprovideanewSocket
while(!available){
try{
wait();
}catch(InterruptedExceptione){
}
}

//NotifytheConnectorthatwehavereceivedthisSocket
Socketsocket=this.socket;
available=false;
notifyAll();

if((debug>=1)&&(socket!=null))
log("Theincomingrequesthasbeenawaited");

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：

/**
*ProcessanincomingTCP/IPconnectiononthespecifiedsocket.Any
*exceptionthatoccursduringprocessingmustbeloggedandswallowed.
*<b>NOTE</b>:ThismethodiscalledfromourConnector'sthread.We
*mustassignittoourownthreadsothatmultiplesimultaneous
*requestscanbehandled.
*
*@paramsocketTCPsockettoprocess
*/
synchronizedvoidassign(Socketsocket){

//WaitfortheProcessortogetthepreviousSocket
while(available){
try{
wait();
}catch(InterruptedExceptione){
}
}

//StorethenewlyavailableSocketandnotifyourthread
this.socket=socket;
available=true;
notifyAll();

if((debug>=1)&&(socket!=null))
log("Anincomingrequestisbeingassigned");

}

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：

/**
*ThebackgroundthreadthatlistensforincomingTCP/IPconnectionsand
*handsthemofftoanappropriateprocessor.
*/
publicvoidrun(){

//Processrequestsuntilwereceiveashutdownsignal
while(!stopped){

//Waitforthenextsockettobeassigned
Socketsocket=await();
if(socket==null)
continue;

//Processtherequestfromthissocket
try{
process(socket);
}catch(Throwablet){
log("process.invoke",t);
}

//Finishupthisrequest
connector.recycle(this);

}

//TellthreadStop()wehaveshutourselvesdownsuccessfully
synchronized(threadSync){
threadSync.notifyAll();
}

}