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为什么thread.interrupt()的作用是这样的?

multithreading java

non sequitor · 技术社区 · 16 年前

这是对Java教程并发代码的修改。

package threads;

public class SimpleThreads {
 static void threadMessage(String msg) {
  String threadName = Thread.currentThread().getName();
  System.out.format("%s: %s%n", threadName,msg);
 }
 private static class MessageLoop implements Runnable{

  @Override
  public void run() {
   // TODO Auto-generated method stub
   String[] importantInfo= {"apple","bat","chlorine","dog","egg","fog","gun"};
   try {
    for(int i=0;i<importantInfo.length;i++) {
     Thread.sleep(4000);
     threadMessage(importantInfo[i]);
    }
   }catch(InterruptedException ie) {
    threadMessage("i wasn't done");
   }
     }
 }
 /**
  * @param args
  */
 public static void main(String[] args) throws InterruptedException{
  // TODO Auto-generated method stub
  long patience = 100;
  if(args.length > 0)
   try {
    patience = Long.parseLong(args[0]) * 1000;
   }catch(NumberFormatException nfe) {
    System.err.println("argument must be a integer");
    System.exit(1);
   }
  threadMessage("starting message loop thread");
  long startTime = System.currentTimeMillis();
  Thread t = new Thread(new MessageLoop());
  t.start();

  threadMessage("waiting for messageloop thread to finish");
  while(t.isAlive()) {
   threadMessage("still waiting...");
   //t.join(1000);
   if(((System.currentTimeMillis() - startTime) > patience) && t.isAlive()) {
    threadMessage("tired of waiting");
    t.interrupt();
    //t.join();
   }
  }
  threadMessage("finally");
 }

}

这就是输出

main: starting message loop thread
main: waiting for messageloop thread to finish
main: still waiting...
main: still waiting...
...(repeats about 100 times)
main: still waiting...
main: still waiting...
main: still waiting...
main: still waiting...
main: tired of waiting
main: still waiting...
main: tired of waiting
main: still waiting...
main: tired of waiting
main: still waiting...
main: tired of waiting
main: still waiting...
main: tired of waiting
Thread-0: i wasn't done
main: finally

我原以为在第一次之后(而且据说只有一次) main: tired of waiting 我会看到 Thread-0: i wasn't done 但是 主:厌倦了等待 出现了5次——为什么?

2 回复 | 直到 16 年前

RickNZ 16 年前

thread.interrupt()只是向目标线程发送一个中断(信号/异常);它不会立即终止它。

此外,在发送中断和目标线程接收和处理中断之间可能存在延迟;上下文切换不能保证是即时的。

您可以通过执行某种形式的阻塞操作(如I/O或睡眠)或调用thread.yield()来鼓励(但不强制)JVM更快地进行上下文切换。

user85421 16 年前

Thread.interrupt() 不杀死或中断线程。
它只是中断一些方法,如睡眠、等待、连接、中断通道上的阻塞I/O或阻塞的选择器。否则,它只设置线程的中断标志,由您来测试这个标志。
如果删除上述代码中的睡眠,中断将没有可见的效果。

线程将(可能)中断几次,因为实际线程(主循环)将继续运行,直到系统更改为中断的线程。中断后,您可以添加sleep()或yield()(join(),如图所示,也应该有效)以允许中断的线程运行。

    threadMessage("tired of waiting");
    t.interrupt();
    t.yield();

也见 documentation of interrupt