使用join和CountDownLatch来等待线程结束

1.join方法的实现

join只能在start()之后调用,

  join 某个线程A,会使当前线程B进入等待,直到线程A结束生命周期(isAlive()==false) ,或者达到给定的时间.

  在此期间内当前线程B处理Waiting(调用 wait()方法),而不是线程A.

  join方法本身只检测线程A的状态,而不影响线程A的执行.

调用线程会等待子线程结束后再运行

public class ThreadJoinTest {

    public static void main(String[] args) {
        int count = 100;
        Thread[] threads = new Thread[count];
        IntStream.range(0, count)
                .forEach(i -> {
                    threads[i] = new Thread("thread" + i) {
                        @Override
                        public void run() {
                            ThreadJoinTest.sleep(1);
                            System.out.println(Thread.currentThread().getName() + ":" + i);
                        }
                    };

                    threads[i].start();
                });

        //join只能在start()之后调用
        //调用线程会等待子线程结束后再运行
        Arrays.stream(threads).forEach(ThreadJoinTest::join);
        System.out.println("over");
}

private static void sleep(int seconds) {
        try {
            TimeUnit.SECONDS.sleep(seconds);
        } catch (InterruptedException ex) {

        }
    }

    private static void join(Thread thread) {
        try {
            thread.join();
        } catch (InterruptedException ex) {

        }
    }

测试结果如下

thread2:2
thread10:10
thread6:6
thread14:14
thread18:18
thread34:34
thread22:22
thread26:26
thread30:30
thread38:38
thread42:42
thread46:46
thread50:50
thread54:54
thread62:62
thread66:66
thread58:58
thread70:70
thread74:74
thread78:78
thread82:82
thread86:86
thread90:90
thread94:94
thread98:98
thread5:5
thread1:1
thread9:9
thread13:13
thread17:17
thread21:21
thread25:25
thread29:29
thread33:33
thread37:37
thread41:41
thread45:45
thread49:49
thread61:61
thread57:57
thread53:53
thread77:77
thread73:73
thread69:69
thread65:65
thread93:93
thread89:89
thread85:85
thread81:81
thread97:97
thread0:0
thread12:12
thread4:4
thread8:8
thread16:16
thread20:20
thread24:24
thread28:28
thread32:32
thread36:36
thread40:40
thread44:44
thread60:60
thread56:56
thread52:52
thread48:48
thread76:76
thread72:72
thread68:68
thread64:64
thread92:92
thread88:88
thread84:84
thread80:80
thread96:96
thread3:3
thread7:7
thread11:11
thread99:99
thread95:95
thread91:91
thread87:87
thread83:83
thread79:79
thread75:75
thread67:67
thread63:63
thread71:71
thread59:59
thread51:51
thread55:55
thread23:23
thread27:27
thread31:31
thread35:35
thread39:39
thread43:43
thread47:47
thread15:15
thread19:19
over

2. java.util.concurrent.CountDownLatch 

public class ThreadJoinTest {

    public static void main(String[] args) {
        int count = 100;
        Thread[] threads = new Thread[count];
       

        java.util.concurrent.CountDownLatch countDownLatch = new java.util.concurrent.CountDownLatch(count);
        IntStream.range(0, count)
                .forEach(i -> {
                    threads[i] = new Thread("thread" + i) {
                        @Override
                        public void run() {
                            ThreadJoinTest.sleep(1);
                            System.out.println(Thread.currentThread().getName() + ":" + i);
                            //只能在run方法的最后一句,或者在 try..finally的 finally里 
                            countDownLatch.countDown();
                        }
                    };

                    threads[i].start();
                });
        try {
            countDownLatch.await();
        } catch (InterruptedException ex) {

        }
        System.out.println("over");
    }