JAVA多线程之扩展ThreadPoolExecutor
ThreadPoolExecutor是可扩展的，通过查看源码可以发现，它提供了几个可以在子类化中改写的方法：beforeExecute,afterExecute,terminated.
源码片段如下所示：
protected void beforeExecute(Thread t, Runnable r) { }
protected void afterExecute(Runnable r, Throwable t) { }
protected void terminated() { }在执行任务的线程中将调用beforeExecute和afterExecute等方法，在这些方法中还可以添加日志、计时、监视或者统计信息收集的功能。无论任务是从run中正常返回，还是抛出一个异常而返回，afterExecute都会被调用。如果任务在完成后带有一个Error，那么就不会调用afterExecute。如果beforeExecute抛出一个RuntimeException，那么任务将不被执行，并且afterExecute也不会被调用。
在线程池完成关闭时调用terminated，也就是在所有任务都已经完成并且所有工作者线程也已经关闭后，terminated可以用来释放Executor在其生命周期里分配的各种资源，此外还可以执行发送通知、记录日志或者手机finalize统计等操作。
下面就以给线程池添加统计信息为例（添加日志和及时等功能）：
package com.threadPool;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.logging.Logger;
public class TimingThreadPool extends ThreadPoolExecutor
{
private final ThreadLocal startTime = new ThreadLocal();
private final Logger log = Logger.getAnonymousLogger();
private final AtomicLong numTasks = new AtomicLong();
private final AtomicLong totalTime = new AtomicLong();
public TimingThreadPool(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
BlockingQueue workQueue)
{
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
protected void beforeExecute(Thread t, Runnable r){
super.beforeExecute(t, r);
log.info(String.format("Thread %s: start %s", t,r));
startTime.set(System.nanoTime());
}
protected void afterExecute(Runnable r, Throwable t){
try{
long endTime = System.nanoTime();
long taskTime = endTime-startTime.get();
numTasks.incrementAndGet();
totalTime.addAndGet(taskTime);
log.info(String.format("Thread %s: end %s, time=%dns", t,r,taskTime));
}
finally
{
super.afterExecute(r, t);
}
}
protected void terminated()
{
try
{
log.info(String.format("Terminated: avg time=%dns",totalTime.get()/numTasks.get()));
}
finally
{
super.terminated();
}
}
}
下面写一个测试类，参考运行效果：
package com.threadPool;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class CheckTimingThreadPool
{
public static void main(String[] args)
{
ThreadPoolExecutor exec = new TimingThreadPool(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue());
exec.execute(new DoSomething(5));
exec.execute(new DoSomething(4));
exec.execute(new DoSomething(3));
exec.execute(new DoSomething(2));
exec.execute(new DoSomething(1));
exec.shutdown();
}
}
class DoSomething implements Runnable{
private int sleepTime;
public DoSomething(int sleepTime)
{
this.sleepTime = sleepTime;
}
@Override
public void run()
{
System.out.println(Thread.currentThread().getName()+" is running.");
try
{
TimeUnit.SECONDS.sleep(sleepTime);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
} 十二月 25, 2015 4:18:42 下午 com.threadPool.TimingThreadPool beforeExecute
信息: Thread Thread[pool-1-thread-1,5,main]: start com.threadPool.DoSomething@43f459c2
十二月 25, 2015 4:18:42 下午 com.threadPool.TimingThreadPool beforeExecute
信息: Thread Thread[pool-1-thread-3,5,main]: start com.threadPool.DoSomething@33891d5d
pool-1-thread-3 is running.
十二月 25, 2015 4:18:42 下午 com.threadPool.TimingThreadPool beforeExecute
信息: Thread Thread[pool-1-thread-4,5,main]: start com.threadPool.DoSomething@33891d5d
pool-1-thread-4 is running.
十二月 25, 2015 4:18:42 下午 com.threadPool.TimingThreadPool beforeExecute
信息: Thread Thread[pool-1-thread-5,5,main]: start com.threadPool.DoSomething@10747b4
pool-1-thread-5 is running.
十二月 25, 2015 4:18:42 下午 com.threadPool.TimingThreadPool beforeExecute
信息: Thread Thread[pool-1-thread-2,5,main]: start com.threadPool.DoSomething@7d4af469
pool-1-thread-2 is running.
pool-1-thread-1 is running.
十二月 25, 2015 4:18:43 下午 com.threadPool.TimingThreadPool afterExecute
信息: Thread null: end com.threadPool.DoSomething@10747b4, time=999589906ns
十二月 25, 2015 4:18:44 下午 com.threadPool.TimingThreadPool afterExecute
信息: Thread null: end com.threadPool.DoSomething@33891d5d, time=1999461618ns
十二月 25, 2015 4:18:45 下午 com.threadPool.TimingThreadPool afterExecute
信息: Thread null: end com.threadPool.DoSomething@33891d5d, time=3000507593ns
十二月 25, 2015 4:18:46 下午 com.threadPool.TimingThreadPool afterExecute
信息: Thread null: end com.threadPool.DoSomething@7d4af469, time=3999691253ns
十二月 25, 2015 4:18:47 下午 com.threadPool.TimingThreadPool afterExecute
信息: Thread null: end com.threadPool.DoSomething@43f459c2, time=4999778490ns
十二月 25, 2015 4:18:47 下午 com.threadPool.TimingThreadPool terminated
信息: Terminated: avg time=2999805772ns
这里说明下TimingThreadPool的构造函数，它直接调用了父类的构造方法，在ThreadPoolExecutor中有许多构造方法，有兴趣的朋友可以查看jdk api或者源码进行查看。
简要说明下构造函数的参数的含义：
corePoolSize:线程池维护线程的最少数量
maximumPoolSize：线程池维护线程的最大数量
keepAliveTime：线程池维护线程所允许的空闲时间
unit：线程池维护所允许的空闲时间的单位
workQueue：线程池所使用的缓存队列