浅谈Java线程Thread.join方法解析

/**   * Waits for this thread to die.   * 调用方线程（调用join方法的线程）执行等待操作，直到被调用的线程（join方法所属的线程）结束，再被唤醒   * <p> An invocation of this method behaves in exactly the same   * way as the invocation   *   *   * @throws InterruptedException   *     if any thread has interrupted the current thread. The   *     <i>interrupted status</i> of the current thread is   *     cleared when this exception is thrown.   */  public final void join() throws InterruptedException {    join(0);  }

/**   * Waits at most {@code millis} milliseconds for this thread to   * die. A timeout of {@code 0} means to wait forever.   * 等待线程执行结束，或者指定的最大等待时间到了，调用方线程再次被唤醒，如果最大等待时间为0，则只能等线程执行结束，才能被唤醒。   * <p> This implementation uses a loop of {@code this.wait} calls   * conditioned on {@code this.isAlive}. As a thread terminates the   * {@code this.notifyAll} method is invoked. It is recommended that   * applications not use {@code wait}, {@code notify}, or   * {@code notifyAll} on {@code Thread} instances.   *   *    */  public final synchronized void join(long millis)  throws InterruptedException {    long base = System.currentTimeMillis();    long now = 0;    if (millis < 0) {      throw new IllegalArgumentException("timeout value is negative");    }    if (millis == 0) {      while (isAlive()) {        wait(0);      }    } else {      while (isAlive()) {        long delay = millis - now;        if (delay <= 0) {          break;        }        wait(delay);        now = System.currentTimeMillis() - base;      }    }  }

//线程退出函数：void JavaThread::exit(bool destroy_vm, ExitType exit_type) ｛...//这里会处理join相关的销毁逻辑ensure_join(this);...｝//处理join相关的销毁逻辑  static void ensure_join(JavaThread* thread) {   Handle threadObj(thread, thread->threadObj());   ObjectLocker lock(threadObj, thread);   thread->clear_pending_exception();   java_lang_Thread::set_thread_status(threadObj(), java_lang_Thread::TERMINATED);   java_lang_Thread::set_thread(threadObj(), NULL);   //这里就调用notifyAll方法，唤醒等待的线程   lock.notify_all(thread);   thread->clear_pending_exception();  }

public class JoinTest {    public static void main(String[] args) {        ThreadBoy boy = new ThreadBoy();    boy.start();      }    static class ThreadBoy extends Thread{    @Override    public void run() {            System.out.println("男孩和女孩准备出去逛街");            ThreadGirl girl = new ThreadGirl();      girl.start();            try {        girl.join();      } catch (InterruptedException e) {        e.printStackTrace();      }            System.out.println("男孩和女孩开始去逛街了");    }  }    static class ThreadGirl extends Thread{    @Override    public void run() {      int time = 5000;            System.out.println("女孩开始化妆,男孩在等待。。。");            try {        Thread.sleep(time);      } catch (InterruptedException e) {        e.printStackTrace();      }            System.out.println("女孩化妆完成！，耗时" + time);          }  }  }

public class JoinTest {    public static void main(String[] args) {        ThreadBoy boy = new ThreadBoy();    boy.start();      }    static class ThreadBoy extends Thread{    @Override    public void run() {            System.out.println("男孩和女孩准备出去逛街");            ThreadGirl girl = new ThreadGirl();      girl.start();            int time = 2000;      try {        girl.join(time);      } catch (InterruptedException e) {        e.printStackTrace();      }            System.out.println("男孩等了" + time + ", 不想再等了，去逛街了");    }  }    static class ThreadGirl extends Thread{    @Override    public void run() {      int time = 5000;            System.out.println("女孩开始化妆,男孩在等待。。。");            try {        Thread.sleep(time);      } catch (InterruptedException e) {        e.printStackTrace();      }            System.out.println("女孩化妆完成！，耗时" + time);          }  }  }