java - 为什么 Thread.interrupt() 会这样？

Question

这是对 Java 并发教程中代码的修改

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

我预计在第一个(而且应该是唯一的)main: tired of waiting 之后我会看到 Thread-0: i wasn't done 但是 main : tired of waiting 出现了 5 次——这是为什么？

Answer 1

Thread.Interrupt() 只是向目标线程发送一个中断(信号/异常)；它不会立即杀死它。

此外，在您发送中断与目标线程接收并处理中断之间可能存在延迟；不保证上下文切换是立即的。

您可以通过执行某种形式的阻塞操作(例如 I/O 或 sleep )或调用 Thread.yield() 来鼓励(但不是强制)JVM 更快地进行上下文切换。