tomcat线程池的配置及源码实现

tomcat中线程池的配置是哎server.xml中：

<Server port="8005" shutdown="SHUTDOWN">    <Service name="Catalina">        <Executor name="tomcatThreadPool" namePrefix="catalina-exec-" maxThreads="150" minSpareThreads="4"/>        <Connector executor="tomcatThreadPool"               port="8080" protocol="HTTP/1.1"               connectionTimeout="20000"               redirectPort="8443" />    </Service></Server>

具体可配置参数如下：

http://tomcat.apache.org/tomcat-7.0-doc/config/executor.html#Standard_Implementation

在tomcat启动的时候，会触发StandardService的 startInternal方法：

protected void startInternal() throws LifecycleException {    setState(LifecycleState.STARTING);    // Start our defined Container first    if (container != null) {        synchronized (container) {            container.start();        }    }    synchronized (executors) {        for (Executor executor: executors) {            executor.start();        }    }    // Start our defined Connectors second    synchronized (connectorsLock) {        for (Connector connector: connectors) {            try {                // If it has already failed, don't try and start it                if (connector.getState() != LifecycleState.FAILED) {                    connector.start();                }            } catch (Exception e) {                log.error(sm.getString(                        "standardService.connector.startFailed",                        connector), e);            }        }    }}

之后触发StandardThreadExecutor的startInternal方法：

@Overrideprotected void startInternal() throws LifecycleException {    taskqueue = new TaskQueue(maxQueueSize);    TaskThreadFactory tf = new TaskThreadFactory(namePrefix,daemon,getThreadPriority());    executor = new ThreadPoolExecutor(getMinSpareThreads(), getMaxThreads(), maxIdleTime, TimeUnit.MILLISECONDS,taskqueue, tf);    executor.setThreadRenewalDelay(threadRenewalDelay);    if (prestartminSpareThreads) {        executor.prestartAllCoreThreads();    }    taskqueue.setParent(executor);    setState(LifecycleState.STARTING);}

此StandardThreadExecutor正是tomcat使用的线程池，类声明如下：

public class StandardThreadExecutor extends LifecycleMBeanBase        implements Executor, ResizableExecutor 

此类内部持有了一个protected ThreadPoolExecutor executor 线程池，具体工作都是委托executor进行处理。

从上面可以看出，在new ThreadPoolExecutor时，会使用在server.xml中配置的参数，如核心线程数，最大线程数等。

另外，线程池的任务队列是一个TaskQueue，该类声明如下：

public class TaskQueue extends LinkedBlockingQueue<Runnable>

其实就是一个LinkedBlockingQueue，如果配置了maxQueueSize，那么就是有界队列，参数maxThreads就会有效，在有界队列满了之后，会继续创建大于核心线程数的线程；如果没有配置maxQueueSize，那么队列的长度默认为Integer.MAX_VALUE，理论上等价于无界队列，此时maxThreads便起不到作用。