sleep,yield,wait,join区别

红太狼 2023-02-12 07:24 19阅读 0赞

### **sleep** ###

有两个重载方法

*  sleep(long millis)  线程睡眠 millis 毫秒
 *  sleep(long millis, int nanos)  线程睡眠 millis 毫秒 + nanos 纳秒

<table> 
 <tbody> 
  <tr> 
   <td style="vertical-align:top;width:104px;"><code>static&nbsp;void</code></td> 
   <td style="width:695px;"><code><strong><a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Thread.html#sleep%28long%29" rel="nofollow">sleep</a></strong>(long&nbsp;millis)</code><br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;在指定的毫秒数内让当前正在执行的线程休眠（暂停执行），此操作受到系统计时器和调度程序精度和准确性的影响。</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:top;width:104px;"><code>static&nbsp;void</code></td> 
   <td style="width:695px;"><code><strong><a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Thread.html#sleep%28long,%20int%29" rel="nofollow">sleep</a></strong>(long&nbsp;millis, int&nbsp;nanos)</code><br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;在指定的毫秒数加指定的纳秒数内让当前正在执行的线程休眠（暂停执行），此操作受到系统计时器和调度程序精度和准确性的影响。</td> 
  </tr> 
 </tbody> 
</table>

public static native void sleep(long millis) throws InterruptedException;
    
    public static void sleep(long millis, int nanos)
            throws InterruptedException {
        if (millis < 0) {
            throw new IllegalArgumentException("timeout value is negative");
        }
    
        if (nanos < 0 || nanos > 999999) {
            throw new IllegalArgumentException(
                    "nanosecond timeout value out of range");
        }
    
        if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
            millis++;
        }
    
        sleep(millis);
    }

sleep

***不会释放锁对象***

在指定的毫秒数内让当前正在执行的线程休眠（暂停执行），此操作受到系统计时器和调度程序精度和准确性的影响。该线程不丢失任何监视器的所属权。

相当于让线程睡眠，交出CPU，让CPU去执行其他的任务。（但是有一点要非常注意，sleep方法不会释放锁，也就是说如果当前线程持有对某个对象的锁，则即使调用sleep方法，其他线程也无法访问这个对象）。当上面一个线程sleep，它不会释放锁，后面的线程都将会被阻塞。当线程睡眠时间满后，不一定会立即得到执行，因为此时可能CPU正在执行其他的任务。所以说调用sleep方法相当于让线程进入阻塞状态。

sleep(0)

Thread.Sleep(0) 并非是真的要线程挂起0毫秒，意义在于这次调用Thread.Sleep(0)的当前线程确实的被冻结了一下，让其他线程有机会优先执行。Thread.Sleep(0) 是你的线程暂时放弃cpu，也就是释放一些未用的时间片给其他线程或进程使用，就相当于一个让位动作。

### yield ###

暂停当前正在执行的线程对象，并执行其他线程。让出cpu的执行权使当前线程由运行态到就绪态。它跟sleep方法类似，同样不会释放锁。但是yield不能控制具体的交出CPU的时间，注意，调用yield方法并不会让线程进入阻塞状态，而是让线程重回就绪状态，它只需要等待重新获取CPU执行时间，这一点是和sleep方法不一样的

public static native void yield();

### wait ###

<table> 
 <tbody> 
  <tr> 
   <td style="vertical-align:top;width:62px;"><code>&nbsp;void</code></td> 
   <td><code><strong><a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#wait%28%29" rel="nofollow">wait</a></strong>()</code><br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;在其他线程调用此对象的&nbsp;<a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#notify%28%29" rel="nofollow"><code>notify()</code></a>&nbsp;方法或&nbsp;<a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#notifyAll%28%29" rel="nofollow"><code>notifyAll()</code></a>&nbsp;方法前，导致当前线程等待。</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:top;width:62px;"><code>&nbsp;void</code></td> 
   <td><code><strong><a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#wait%28long%29" rel="nofollow">wait</a></strong>(long&nbsp;timeout)</code><br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;在其他线程调用此对象的&nbsp;<a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#notify%28%29" rel="nofollow"><code>notify()</code></a>&nbsp;方法或&nbsp;<a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#notifyAll%28%29" rel="nofollow"><code>notifyAll()</code></a>&nbsp;方法，或者超过指定的时间量前，导致当前线程等待。</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:top;width:62px;"><code>&nbsp;void</code></td> 
   <td><code><strong><a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#wait%28long,%20int%29" rel="nofollow">wait</a></strong>(long&nbsp;timeout, int&nbsp;nanos)</code><br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;在其他线程调用此对象的&nbsp;<a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#notify%28%29" rel="nofollow"><code>notify()</code></a>&nbsp;方法或&nbsp;<a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Object.html#notifyAll%28%29" rel="nofollow"><code>notifyAll()</code></a>&nbsp;方法，或者其他某个线程中断当前线程，或者已超过某个实际时间量前，导致当前线程等待。</td> 
  </tr> 
 </tbody> 
</table>

wait会释放锁对象。

public final void wait() throws InterruptedException {
        wait(0);
    }
    public final void wait(long timeout, int nanos) throws InterruptedException {
        if (timeout < 0) {
            throw new IllegalArgumentException("timeout value is negative");
        }
    
        if (nanos < 0 || nanos > 999999) {
            throw new IllegalArgumentException(
                    "nanosecond timeout value out of range");
        }
    
        if (nanos > 0) {
            timeout++;
        }
    
        wait(timeout);
    }
    public final native void wait(long timeout) throws InterruptedException;

### join ###

<table> 
 <tbody> 
  <tr> 
   <td style="vertical-align:top;"><code>&nbsp;void</code></td> 
   <td><code><strong><a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Thread.html#join%28%29" rel="nofollow">join</a></strong>()</code><br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;等待该线程终止。</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:top;"><code>&nbsp;void</code></td> 
   <td><code><strong><a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Thread.html#join%28long%29" rel="nofollow">join</a></strong>(long&nbsp;millis)</code><br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;等待该线程终止的时间最长为&nbsp;<code>millis</code>&nbsp;毫秒。</td> 
  </tr> 
  <tr> 
   <td style="vertical-align:top;"><code>&nbsp;void</code></td> 
   <td><code><strong><a href="https://tool.oschina.net/uploads/apidocs/jdk-zh/java/lang/Thread.html#join%28long,%20int%29" rel="nofollow">join</a></strong>(long&nbsp;millis, int&nbsp;nanos)</code><br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;等待该线程终止的时间最长为&nbsp;<code>millis</code>&nbsp;毫秒 +&nbsp;<code>nanos</code>&nbsp;纳秒。</td> 
  </tr> 
 </tbody> 
</table>

等待该线程终止的时间最长为 `millis` 毫秒。超时为 `0` 意味着要一直等下去。join方法依赖于最终调用wait方法

假如在main线程中，调用thread.join方法，则main方法会等待thread线程执行完毕或者等待一定的时间。如果调用的是无参join方法，则等待thread执行完毕，如果调用的是指定了时间参数的join方法，则等待一定的时间

public final void join() throws InterruptedException {
        join(0);
    }
    
    public final synchronized void join(long millis, int nanos)
            throws InterruptedException {
    
        if (millis < 0) {
            throw new IllegalArgumentException("timeout value is negative");
        }
    
        if (nanos < 0 || nanos > 999999) {
            throw new IllegalArgumentException(
                    "nanosecond timeout value out of range");
        }
    
        if (nanos >= 500000 || (nanos != 0 && millis == 0)) {
            millis++;
        }
    
        join(millis);
    }
    public final synchronized void join(long millis)
            throws InterruptedException {
        long base = System.currentTimeMillis();
        long now = 0;
    
        if (millis < 0) {
            throw new IllegalArgumentException("timeout value is negative");
        }
    
        if (millis == 0) {
            while (isAlive()) {
                wait(0);
            }
        } else {
            while (isAlive()) {
                long delay = millis - now;
                if (delay <= 0) {
                    break;
                }
                wait(delay);
                now = System.currentTimeMillis() - base;
            }
        }
    }