ThreadPoolExecutor介绍

ThreadPoolExecutor的说明

ThreadPoolExecutor常见的操作主要有以下几个方法：

1. getPoolSize()：返回线程池实际的线程数。
2. getActiveCount()：返回在执行者中正在执行任务的线程数。
3. getCompletedTaskCount()：返回执行者完成的任务数。
4. submit(): 提交一个线程给线程执行者，如果执行者有空余线程，则直接执行；否则等待直到有空闲线程。这里调用sumbit后，并不会阻塞调用线程。调用者所在的线程和执行的线程并发运行。

下面要着重介绍两个方法：

1. shutdown(): 调用这个方法后，线程执行者在完成当前已经提交的所有任务后，结束运行。
   a. 在主线程中如果调用线程执行者的这个方法，并不会使线程执行者中已经submit的任务中断（无论是待执行、执行中）
   b. 调用shutdown会通知执行者，后面提交的任务“不允许接受”，在shutdown后提交任务，会抛出RejectedExecutionException的异常信息。
2. shutdownNow(): 调用这个方法后，立即停止执行者的运行。返回待执行的Task。
   a. 中断所有正在执行的线程: 正在执行的线程会收到中断信息。抛出InterruptedException
   b. 后面提交的任务“不允许接受”，在shutdownNow后再调用submit提交任务，会抛出RejectedExecutionException的异常信息。

code1：

public class ThreadPoolTest {
    public static void main(String[] args) {
        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
        for (int i = 0; i < 3; i++) {
            executor.submit(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(100);
                        System.out.println("sub thread classs");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        executor.shutdown();
        System.out.println("Main classs");
    }
}

结果：

Main classs
sub thread classs
sub thread classs
sub thread classs

说明：
调用executor.submit后，并不会阻塞主线程。主线程和提交到执行者中的线程并发执行。

code2：

public class ThreadPoolTest {
    public static void main(String[] args) {
        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
        for (int i = 0; i < 3; i++) {
            executor.submit(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(100);
                        System.out.println("sub thread classs");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        executor.shutdown();
        executor.submit(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(100);
                    System.out.println("sub thread classs");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        System.out.println("Main classs");
    }
}

结果：

Exception in thread "main" java.util.concurrent.RejectedExecutionException: Task 
java.util.concurrent.FutureTask@1c910477 rejected from java.util.concurrent.
ThreadPoolExecutor@74bc2f47[Shutting down, pool size = 3, active threads = 3, queued tasks = 0, completed tasks = 0]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:110)
at ThreadPoolTest.ThreadPoolTest.main(ThreadPoolTest.java:29)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
sub thread classs
sub thread classs
sub thread classs

说明：
调用executor.shutdown()后，如果再调用submit()方法，调用线程会抛出rejectedExecution，如果没有try，cacth直接中断
后续的操作。

code3：

public class ThreadPoolTest {
    public static void main(String[] args) {
        ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
        for (int i = 0; i < 3; i++) {
            executor.submit(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(100);
                        System.out.println("sub thread classs");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        List<Runnable> list=executor.shutdownNow();
        System.out.println("list size:"+list.size());
        executor.submit(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(100);
                    System.out.println("sub thread classs");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        System.out.println("Main classs");
    }
}

结果：

list size:0
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at ThreadPoolTest.ThreadPoolTest$1.run(ThreadPoolTest.java:16)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at ThreadPoolTest.ThreadPoolTest$1.run(ThreadPoolTest.java:16)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)
java.lang.InterruptedException: sleep interrupted
at java.lang.Thread.sleep(Native Method)
at ThreadPoolTest.ThreadPoolTest$1.run(ThreadPoolTest.java:16)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)
Exception in thread "main" java.util.concurrent.RejectedExecutionException: Task 
java.util.concurrent.FutureTask@3a9d04dc rejected from java.util.concurrent.ThreadPoolExecutor@1aaa2594
[Shutting down, pool size = 2, active threads = 2, queued tasks = 0, completed tasks = 1]
at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2048)
at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:821)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1372)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:110)
at ThreadPoolTest.ThreadPoolTest.main(ThreadPoolTest.java:25)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)

说明：
调用shutDownNow()后，直接中断所有的线程。并且后面submit()task会抛出rejectedExecution。