Java 简明教程

Java - Thread Control

Java Thread Control

核心 Java 提供了对 multithreaded 程序的完全控制。你可以开发一个多线程程序，根据需要挂起、恢复或完全停止它。你可以使用很多线程对象上的静态方法来控制其行为。

Methods for Controlling Java Thread

下表列出了在 Java 中用于控制 thread 的方法：−

Sr.No.

Method & Description

1

public void suspend() 此方法会使一个线程进入挂起状态，可以使用 resume() 方法恢复。

2

public void stop() 此方法会完全停止一个线程。

3

public void resume() 此方法会恢复一个线程，该线程使用 suspend() 方法挂起。

4

public void wait() 导致电流线程在另一个线程调用 notify() 之前处于等待状态。

5

public void notify() 唤醒一个正在等待该对象监视器的单个线程。

注意，Java 的最新版本已声明 suspend( )、resume( ) 和 stop( ) 方法已弃用，因此你需要使用可用的替代方法。

Example of Thread Control in Java

class RunnableDemo implements Runnable {
   public Thread t;
   private String threadName;
   boolean suspended = false;

   RunnableDemo( String name) {
      threadName = name;
      System.out.println("Creating " +  threadName );
   }

   public void run() {
      System.out.println("Running " +  threadName );
      try {
         for(int i = 10; i > 0; i--) {
            System.out.println("Thread: " + threadName + ", " + i);
            // Let the thread sleep for a while.
            Thread.sleep(300);
            synchronized(this) {
               while(suspended) {
                  wait();
               }
            }
         }
      } catch (InterruptedException e) {
         System.out.println("Thread " +  threadName + " interrupted.");
      }
      System.out.println("Thread " +  threadName + " exiting.");
   }

   public void start () {
      System.out.println("Starting " +  threadName );
      if (t == null) {
         t = new Thread (this, threadName);
         t.start ();
      }
   }

   void suspend() {
      suspended = true;
   }

   synchronized void resume() {
      suspended = false;
      notify();
   }
}

public class TestThread {

   public static void main(String args[]) {

      RunnableDemo R1 = new RunnableDemo( "Thread-1");
      R1.start();

      RunnableDemo R2 = new RunnableDemo( "Thread-2");
      R2.start();

      try {
         Thread.sleep(1000);
         R1.suspend();
         System.out.println("Suspending First Thread");
         Thread.sleep(1000);
         R1.resume();
         System.out.println("Resuming First Thread");

         R2.suspend();
         System.out.println("Suspending thread Two");
         Thread.sleep(1000);
         R2.resume();
         System.out.println("Resuming thread Two");
      } catch (InterruptedException e) {
         System.out.println("Main thread Interrupted");
      }try {
         System.out.println("Waiting for threads to finish.");
         R1.t.join();
         R2.t.join();
      } catch (InterruptedException e) {
         System.out.println("Main thread Interrupted");
      }
      System.out.println("Main thread exiting.");
   }
}

以上程序产生以下输出 −

Output

Creating Thread-1
Starting Thread-1
Creating Thread-2
Starting Thread-2
Running Thread-1
Thread: Thread-1, 10
Running Thread-2
Thread: Thread-2, 10
Thread: Thread-1, 9
Thread: Thread-2, 9
Thread: Thread-1, 8
Thread: Thread-2, 8
Thread: Thread-1, 7
Thread: Thread-2, 7
Suspending First Thread
Thread: Thread-2, 6
Thread: Thread-2, 5
Thread: Thread-2, 4
Resuming First Thread
Suspending thread Two
Thread: Thread-1, 6
Thread: Thread-1, 5
Thread: Thread-1, 4
Thread: Thread-1, 3
Resuming thread Two
Thread: Thread-2, 3
Waiting for threads to finish.
Thread: Thread-1, 2
Thread: Thread-2, 2
Thread: Thread-1, 1
Thread: Thread-2, 1
Thread Thread-1 exiting.
Thread Thread-2 exiting.
Main thread exiting.