Java中的wait和sleep

Z时代
2024-01-10
分类：综合

java

sleep()和wait()

首先，Java中的多线程是一种抢占式的机制，而不是分时机制。抢占式的机制是有多个线程处于可运行状态，但是只有一个线程在运行。

这种机制决定了，对于同一对象的多线程访问，必须考虑同步的问题，synchronize的意义在这。

几个区别：

sleep是Thread类的方法，用于线程自身的控制；wait是Object类的方法，用于线程之间的控制，配套的方法是Object·的notify和notifyAll方法。

sleep与锁没有关系，如果在锁之中，不会释放锁。wait存在于锁之中，会释放当前的锁，等待被唤醒（notify）。

sleep必须捕获异常，而wait，notify和notifyAll不需要捕获异常。但在 sleep的过程中过程中有可能被其他对象调用它的interrupt()，产生InterruptedException异常，如果你的程序不捕获这个异常，线程就会异常终止，进入TERMINATED状态，如果你的程序捕获了这个异常，那么程序就会继续执行catch语句块（可能还有finally语句块）以及以后的代码。注意sleep()方法是一个静态方法，也就是说他只对当前对象有效，不能通过t.sleep()让t对象进入sleep。

JDK8关于这两个的解释：

    /**
     * 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.
     */
    public static native void sleep(long millis) throws InterruptedException;

sleep方法总结为：

使当前运行的线程休眠，该线程不会丢失对任何监视器的所有权。

   /**
     * 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 (&lt;condition does not hold&gt;)
     *             obj.wait();
     *         ... // Perform action appropriate to condition
     *     }
     * </pre>
      public final void wait() throws InterruptedException {
        wait(0);
    }