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。

Core Java provides complete control over multithreaded program. You can develop a multithreaded program which can be suspended, resumed, or stopped completely based on your requirements. There are various static methods which you can use on thread objects to control their behavior.

Methods for Controlling Java Thread

下表列出了在 Java 中用于控制 thread 的方法：−

Following table lists down the methods for controlling a thread in Java: −

Sr.No.

Method & Description

1

public void suspend() This method puts a thread in the suspended state and can be resumed using resume() method.

2

public void stop() This method stops a thread completely.

3

public void resume() This method resumes a thread, which was suspended using suspend() method.

4

public void wait() Causes the current thread to wait until another thread invokes the notify().

5

public void notify() Wakes up a single thread that is waiting on this object’s monitor.

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。

Be aware that the latest versions of Java has deprecated the usage of suspend( ), resume( ), and stop( ) methods and so you need to use available alternatives.

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 −

The above program produces the following output −

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.