代码分析Java中线程的等待与唤醒

时间:2021-09-17 03:08:05

我们先来看一下实例代码:

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class threada extends thread{
 
  public threada(string name) {
    super(name);
  }
 
  public void run() {
    synchronized (this) {
      system.out.println(thread.currentthread().getname()+" call notify()");
      notify();
    }
  }
}
public class waittest {
  public static void main(string[] args) {
    threada t1 = new threada("t1");
    synchronized(t1) {
      try {
        // 启动“线程t1”
        system.out.println(thread.currentthread().getname()+" start t1");
        t1.start();
 
        // 主线程等待t1通过notify()唤醒。
        system.out.println(thread.currentthread().getname()+" wait()");
        t1.wait();
 
        system.out.println(thread.currentthread().getname()+" continue");
      } catch (interruptedexception e) {
        e.printstacktrace();
      }
    }
  }
}

输出结果:main start t1 -> main wait() -> t1 call notify() -> main continue

其实调用t1.start(),t1为就绪状态,只是main方法中,t1被main线程锁住了,t1.wait()的时候,让当前线程等待,其实是让main线程等待了,然后释放了t1锁,t1线程执行,打印t1 call notify(),然后唤醒main线程,最后结束;

这里说一下wait()与sleep()的区别,他们的共同点都是让线程休眠,但是wait()会释放对象同步锁,而sleep()不会;下面的代码t1结束之后才会运行t2;能够证实这一点;

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public class sleeplocktest{
  private static object obj = new object();
  public static void main(string[] args){
    threada t1 = new threada("t1");
    threada t2 = new threada("t2");
    t1.start();
    t2.start();
  }
  static class threada extends thread{
    public threada(string name){
      super(name);
    }
    public void run(){
      synchronized (obj) {
        try {
          for(int i=0; i <10; i++){
            system.out.printf("%s: %d\n", this.getname(), i);
            // i能被4整除时,休眠100毫秒
            if (i%4 == 0)
              thread.sleep(100);
          }
        } catch (interruptedexception e) {
          e.printstacktrace();
        }
      }
    }
  }
}