多线程：（六）初入线程池

这两天有点困、累，可能是公司任务太少，一松懈，疲劳都上来了，也可能是自己老了吧，O(∩_∩)O哈哈~

概述一下子：

根据系统的环境情况，可以自动或手动设置线程数量，达到运行的最佳效果；少了浪费了系统资源，多了造成系统拥挤效率不高。用线程池控制线程数量，其他线程排队等候。一个任务执行完毕，再从队列的中取最前面的任务开始执行。

线程池减少了创建和销毁线程的次数，每个工作线程都可以被重复利用，可执行多个任务。

上代码，读逻辑，Go！

/**
 * 十个任务，每个任务执行十次
 * @author yang
 */
public class ThreadPoolTest {

    public static void main(String[] args) {
        //固定线程数量的线程池
        ExecutorService threadPool = Executors.newFixedThreadPool(3);
        //线程池的大小依赖于操作系统（或者说JVM）
        // ExecutorService threadPool = Executors.newCachedThreadPool();
        //单个线程的线程池：只有一个线程在工作，如果这个线程异常结束，则会立刻有一个新线程替代它
        // ExecutorService threadPool = Executors.newSingleThreadExecutor();

        for (int i = 1; i <= 10; i++) {
            final int task = i;
            threadPool.execute(new Runnable() {
                @Override
                public void run() {
                    for (int j = 1; j <= 10; j++) {
                        try {
                            Thread.sleep(20);
                        } catch (InterruptedException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                        System.out.println(Thread.currentThread().getName() + " is looping of " + j + " for  task of " + task);
                    }
                }
            });
        }
        // threadPool.shutdown();       //结束线程池

        //附带一个定时任务，O(∩_∩)O哈哈~
        Executors.newScheduledThreadPool(3).scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                System.out.println("bombing!");

            }
        }, 6, 2, TimeUnit.SECONDS);
    }

}

部分打印结果（因为线程池里开了3个线程，所以3个任务同时执行完十次以后，再接着往后同时执行3个任务）：
pool-1-thread-2 is looping of 1 for  task of 2
pool-1-thread-1 is looping of 1 for  task of 1
pool-1-thread-3 is looping of 1 for  task of 3
pool-1-thread-1 is looping of 2 for  task of 1
pool-1-thread-3 is looping of 2 for  task of 3
pool-1-thread-2 is looping of 2 for  task of 2
pool-1-thread-2 is looping of 3 for  task of 2
pool-1-thread-3 is looping of 3 for  task of 3
pool-1-thread-1 is looping of 3 for  task of 1
pool-1-thread-1 is looping of 4 for  task of 1
pool-1-thread-2 is looping of 4 for  task of 2
pool-1-thread-3 is looping of 4 for  task of 3
pool-1-thread-3 is looping of 5 for  task of 3
pool-1-thread-1 is looping of 5 for  task of 1
pool-1-thread-2 is looping of 5 for  task of 2
pool-1-thread-3 is looping of 6 for  task of 3
pool-1-thread-2 is looping of 6 for  task of 2
pool-1-thread-1 is looping of 6 for  task of 1
pool-1-thread-2 is looping of 7 for  task of 2
pool-1-thread-1 is looping of 7 for  task of 1
pool-1-thread-3 is looping of 7 for  task of 3
pool-1-thread-2 is looping of 8 for  task of 2
pool-1-thread-1 is looping of 8 for  task of 1
pool-1-thread-3 is looping of 8 for  task of 3
pool-1-thread-1 is looping of 9 for  task of 1
pool-1-thread-3 is looping of 9 for  task of 3
pool-1-thread-2 is looping of 9 for  task of 2
pool-1-thread-3 is looping of 10 for  task of 3
pool-1-thread-2 is looping of 10 for  task of 2
pool-1-thread-1 is looping of 10 for  task of 1
pool-1-thread-3 is looping of 1 for  task of 4
pool-1-thread-1 is looping of 1 for  task of 5
pool-1-thread-2 is looping of 1 for  task of 6
pool-1-thread-1 is looping of 2 for  task of 5
pool-1-thread-3 is looping of 2 for  task of 4
pool-1-thread-2 is looping of 2 for  task of 6

好了，简洁总结，深刻理解。有不对的地方，欢迎指出，在此谢过。

原文：多线程：（六）初入线程池

那时年少轻狂，把喜欢当做筹码，才敢肆无忌惮的任性。
----那时年少轻狂