如何通过另一个线程停止一个线程？

Question

我在Java中的线程上有些挣扎，我有三个线程-
线程1，线程2和线程3。那些启动时正在执行某些任务，我想通过thread1停止这两个线程。我将thread1放在sleep(500)，然后停止两个线程，但是两个线程的进程仍在运行。你有什么想法吗？

Answer 1

您如何试图阻止他们？Thread.stop？警告此方法已弃用。

而是考虑对线程1使用某种标志来与线程2和3通信，它们应该停止。实际上，您可能会使用interrupts。

下面，使用Thread.interrupt来实现协调。

final Thread subject1 = new Thread(new Runnable() {

  public void run() {
    while (!Thread.interrupted()) {
      Thread.yield();
    }
    System.out.println("subject 1 stopped!");
  }
});
final Thread subject2 = new Thread(new Runnable() {

  public void run() {
    while (!Thread.interrupted()) {
      Thread.yield();
    }
    System.out.println("subject 2 stopped!");
  }
});
final Thread coordinator = new Thread(new Runnable() {

  public void run() {
    try {
      Thread.sleep(500);
    } catch (InterruptedException ex) { }
    System.out.println("coordinator stopping!");
    subject1.interrupt();
    subject2.interrupt();
  }
});
subject1.start();
subject2.start();
coordinator.start();

或者，您也可以使用volatile boolean（或AtomicBoolean）作为通信方式。
由提供的原子访问，volatile并java.util.concurrent.atomic.*允许您确保主题线程可以看到该标志的突变。

final AtomicBoolean running = new AtomicBoolean(true);

final ExecutorService subjects = Executors.newFixedThreadPool(2);
subjects.submit(new Runnable() {

  public void run() {
    while (running.get()) {
      Thread.yield();
    }
    System.out.println("subject 1 stopped!");
  }
});
subjects.submit(new Runnable() {

  public void run() {
    while (running.get()) {
      Thread.yield();
    }
    System.out.println("subject 2 stopped!");
  }
});
final ScheduledExecutorService coordinator = Executors.newSingleThreadScheduledExecutor();
coordinator.schedule(new Runnable() {

  public void run() {
    System.out.println("coordinator stopping!");
    running.set(false);
    subjects.shutdown();
    coordinator.shutdown();
  }
}, 500, TimeUnit.MILLISECONDS);

同样，您可以选择使用而不是使用AtomicBoolean，例如：

static volatile boolean running = true;

更好的是，如果您利用ExecutorService，还可以编写类似的代码，如下所示：

final ExecutorService subjects = Executors.newFixedThreadPool(2);
subjects.submit(new Runnable() {

  public void run() {
    while (!Thread.interrupted()) {
      Thread.yield();
    }
    System.out.println("subject 1 stopped!");
  }
});
subjects.submit(new Runnable() {

  public void run() {
    while (!Thread.interrupted()) {
      Thread.yield();
    }
    System.out.println("subject 2 stopped!");
  }
});
final ScheduledExecutorService coordinator = Executors.newSingleThreadScheduledExecutor();
coordinator.schedule(new Runnable() {

  public void run() {
    System.out.println("coordinator stopping!");
    subjects.shutdownNow();
    coordinator.shutdown();
  }
}, 500, TimeUnit.MILLISECONDS);

这利用了ThreadPoolExecutor.shutdownNow中断其工作线程以试图发出关闭信号这一事实。

运行任何示例，输出应具有以下效果：

C:\dev\scrap>javac CoordinationTest.java

C:\dev\scrap>java CoordinationTest
coordinator stopping!
subject 1 stopped!
subject 2 stopped!

请注意，最后两行可以任意顺序排列。