保证三个线程依次按顺序执行

保证三个线程依次按顺序执行

废话不多说，下面贴代码

final Thread t1 = new Thread(new Runnable() {
public void run() {
System.out.println(Thread.currentThread().getName() + " run 1");
}
}, "T1");
final Thread t2 = new Thread(new Runnable() {
public void run() {
System.out.println(Thread.currentThread().getName() + " run 2");
try {
t1.join(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "T2");
final Thread t3 = new Thread(new Runnable() {
public void run() {
System.out.println(Thread.currentThread().getName() + " run 3");
try {
t2.join(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "T3");
t1.start();
t2.start();
t3.start();
}

在这里我在t2的线程里面t1 的join方法，抢占时间片，然后在t3的线程里面，抢占t2的时间片，理应是 t3执行>t2执行>t1执行，可以到最后结果的时候，每次的结果都不尽相同，这让我很纳闷，有兴趣的同学可以尝试一下。欢迎互相讨论。在这里我就去翻看线程的文档，发现了newSingleThreadExecutor 这个线程池，保证线程里面的任务依次执行，很兴奋public class TestJoin {public static void main(String[] args) throws InterruptedException {final Thread t1 = new Thread(new Runnable() {public void run() {System.out.println(Thread.currentThread().getName() + " run 1");}}, "T1");final Thread t2 = new Thread(new Runnable() {public void run() {System.out.println(Thread.currentThread().getName() + " run 2");try {t1.join(10);} catch (InterruptedException e) {e.printStackTrace();}}}, "T2");final Thread t3 = new Thread(new Runnable() {public void run() {System.out.println(Thread.currentThread().getName() + " run 3");try {t2.join(10);} catch (InterruptedException e) {e.printStackTrace();}}}, "T3");// method1//t1.start();//t2.start();//t3.start();// method 2 使用 单个任务的线程池来实现。保证线程的依次执行ExecutorService executor = Executors.newSingleThreadExecutor();executor.submit(t1);executor.submit(t2);executor.submit(t3);executor.shutdown();}}

在这里发现结果每次都是 t1执行，t2执行，t3执行，这里达到目的了之后，不禁回想，这个Single线程池为啥这么好用，不由得就像把线程池狠狠的看一遍，然后就去翻看了源代码

    /*** Creates an Executor that uses a single worker thread operating* off an unbounded queue. (Note however that if this single* thread terminates due to a failure during execution prior to* shutdown, a new one will take its place if needed to execute* subsequent tasks.)  Tasks are guaranteed to execute* sequentially, and no more than one task will be active at any* given time. Unlike the otherwise equivalent* {@code newFixedThreadPool(1)} the returned executor is* guaranteed not to be reconfigurable to use additional threads.** @return the newly created single-threaded Executor*/public static ExecutorService newSingleThreadExecutor() {return new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1,0L, TimeUnit.MILLISECONDS,4000new LinkedBlockingQueue<Runnable>()));}

12345678910111213141516171819大致意思是:创建一个只有一个线程的线程池来操作不限数量的队列，也就是把线程放进了一个队列中，队列我们都知道是FIFO的。SingleThreadExecutor的工作线程只有一个，其他队列中的线程都处于休眠，也就是sleep状态，当这个worker线程做完事了，也就是run方法运行结束，就又从队列中拿出一个休眠线程（sleep）出来唤醒（notify），这样依次把队列中的所有线程处理完毕，这样并没有结束，如果线程池中没有待处理的线程，线程池一直会等待，等待下一次任务的提交，除非把线程池给shutdown掉，这样线程池的生命周期才算完毕。