ThreadPoolExecutor 的 shutdown（） 和shutdownNow（）

public List<Runnable> shutdownNow() {
List<Runnable> tasks;
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
advanceRunState(STOP);
interruptWorkers();
tasks = drainQueue();
} finally {
mainLock.unlock();
}
tryTerminate();
return tasks;
}
public void shutdown() {
final ReentrantLock mainLock = this.mainLock;
mainLock.lock();
try {
checkShutdownAccess();
advanceRunState(SHUTDOWN);
interruptIdleWorkers();
onShutdown(); // hook for ScheduledThreadPoolExecutor
} finally {
mainLock.unlock();
}
tryTerminate();
} 对比其代码可知 shutdown 只是将空闲的线程interrupt() 了， 因此在shutdown（）之前提交的任务可以继续执行直到结束。而shutdownNow 是interrupt所有线程， 因此大部分线程将立刻被中断。之所以是大部分，而不是全部 ，是因为interrupt()方法能力有限。如果线程中没有sleep 、wait、Condition、定时锁等应用, interrupt()方法是无法中断当前的线程的。所以，ShutdownNow()并不代表线程池就一定立即就能退出，它可能必须要等待所有正在执行的任务都执行完成了才能退出。
例如下面这种情况 将一直打印 go to sleeppackage edu.neu.xiaobing.concurrent;import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;public class Interrupt { /**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub ExecutorService executor = Executors.newCachedThreadPool();
executor.execute(new Interrupt().new MyRunnable());
executor.shutdownNow();
}

class MyRunnable implements Runnable{ @Override
public void run() {
// TODO Auto-generated method stub
while(true){
System.out.println("go to sleep");
// try {
//
// Thread.sleep(100000);
//
// } catch (InterruptedException e) {
// // TODO Auto-generated catch block
// e.printStackTrace();
// System.out.println("sleeping");
// }
}
}

}}