Java并发常用方法 sleep 和 wait

一时失言乱红尘 2022-02-18 09:43 178阅读 0赞

## **一：sleep 和 wait** ##

sleep()方法：

1.  功能：让当前线程休眠指定时间，休眠时间的准确性依赖于系统时钟和CPU调度机制
2.  是Thread类的静态方法
3.  可在任何地方调用，需要处理InterruptedException
4.  当前线程调用sleep()方法，当前线程会进入[阻塞状态][Link 1]，sleep()结束进入[可执行状态][Link 1]
5.  sleep()方法不释放已获取的锁资源

wait()方法：

1.  让当前线程进入等待状态，当别的其他线程调用notify()或者notifyAll()方法时，当前线程进入[可运行状态][Link 1]
2.  是Object类的成员方法
3.  wait方法必须在同步上下文中调用，例如：同步方法块或者同步方法中，这也就意味着如果你想要调用wait方法，前提是必须获取对象上的锁资源
4.  当wait方法调用时，当前线程将会释放已获取的对象锁资源，并进入等待队列，其他线程就可以尝试获取对象上的锁资源

sleep() vs wait()

<table> 
 <thead> 
  <tr> 
   <th></th> 
   <th>sleep</th> 
   <th>wait</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>同步</td> 
   <td>不需要在同步方法或同步块中调用</td> 
   <td>只能在同步上下文中调用wait方法，否则或抛出IllegalMonitorStateException异常</td> 
  </tr> 
  <tr> 
   <td>作用对象</td> 
   <td>定义在java.lang.Thread中，作用于当前线程</td> 
   <td>定义在Object类中，作用于对象本身</td> 
  </tr> 
  <tr> 
   <td>释放锁资源</td> 
   <td>否</td> 
   <td>是</td> 
  </tr> 
  <tr> 
   <td>唤醒条件</td> 
   <td>超时或者调用interrupt()方法</td> 
   <td>其他线程调用对象的notify()或者notifyAll()方法</td> 
  </tr> 
  <tr> 
   <td>方法属性</td> 
   <td>sleep是静态方法</td> 
   <td>wait是实例方法</td> 
  </tr> 
 </tbody> 
</table>

## **二：方法签名：** ##

**sleep()方法是Thread类的静态方法**

/** * Causes the currently executing thread to sleep (temporarily cease * execution) for the specified number of milliseconds, subject to * the precision and accuracy of system timers and schedulers. The thread * does not lose ownership of any monitors. * * @param millis * the length of time to sleep in milliseconds * * @throws IllegalArgumentException * if the value of {@code millis} is negative * * @throws InterruptedException * if any thread has interrupted the current thread. The * <i>interrupted status</i> of the current thread is * cleared when this exception is thrown. */
        public static native void sleep(long millis) throws InterruptedException;

**wait()方法是Object类的成员方法**

/** * Causes the current thread to wait until another thread invokes the * {@link java.lang.Object#notify()} method or the * {@link java.lang.Object#notifyAll()} method for this object. * In other words, this method behaves exactly as if it simply * performs the call {@code wait(0)}. * <p> * The current thread must own this object's monitor. The thread * releases ownership of this monitor and waits until another thread * notifies threads waiting on this object's monitor to wake up * either through a call to the {@code notify} method or the * {@code notifyAll} method. The thread then waits until it can * re-obtain ownership of the monitor and resumes execution. * <p> * As in the one argument version, interrupts and spurious wakeups are * possible, and this method should always be used in a loop: * <pre> * synchronized (obj) { * while (<condition does not hold>) * obj.wait(); * ... // Perform action appropriate to condition * } * </pre> * This method should only be called by a thread that is the owner * of this object's monitor. See the {@code notify} method for a * description of the ways in which a thread can become the owner of * a monitor. * * @throws IllegalMonitorStateException if the current thread is not * the owner of the object's monitor. * @throws InterruptedException if any thread interrupted the * current thread before or while the current thread * was waiting for a notification. The <i>interrupted * status</i> of the current thread is cleared when * this exception is thrown. * @see java.lang.Object#notify() * @see java.lang.Object#notifyAll() */
        public final void wait() throws InterruptedException { 
            wait(0);
        }

[Link 1]: https://blog.csdn.net/zhaohong_bo/article/details/89290483