LockSupport類在jdk源碼中基本定義就是創建鎖和其他同步類的 基本線程阻塞原語,直接與UnSafe類打交道，Unsafe類中眾多的native方法實現都是基于C++語言的，而且與系統平臺相關，這里基本不做闡述。這里主要說明LockSupport的使用方式。

常見使用方式

LockSupport.park()
LockSupport.unpark(Thread t)

park()方法會阻塞當前線程(線程進入Waiting狀態)，除非它獲取了"許可證"。
unpark(Thread t)方法會給線程t頒發一個"許可證"。

從park()方法的官方注釋中，我們發現還有其他的方式可以使park()方法返回。

    /**
     * Disables the current thread for thread scheduling purposes unless the
     * permit is available.
     *
     * <p>If the permit is available then it is consumed and the call
     * returns immediately; otherwise the current thread becomes disabled
     * for thread scheduling purposes and lies dormant until one of three
     * things happens:
     *
     * <ul>
     *
     * <li>Some other thread invokes {@link #unpark unpark} with the
     * current thread as the target; or
     *
     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
     * the current thread; or
     *
     * <li>The call spuriously (that is, for no reason) returns.
     * </ul>
     *
     * <p>This method does <em>not</em> report which of these caused the
     * method to return. Callers should re-check the conditions which caused
     * the thread to park in the first place. Callers may also determine,
     * for example, the interrupt status of the thread upon return.
     */
    public static void park() {
        UNSAFE.park(false, 0L);
    }

三種原因中的第二種是其他線程中斷線程t時，線程t會從park()方法返回。測試代碼如下:

public class LockSupportUse {
    public static void main(String[] args) {
        testParkThenInterrupt();
    }

    public static void testParkThenInterrupt(){
        Thread thread = new Thread(new LockSupportThread(), "LockSupportThread");
        thread.start();

        SleepUtil.sleep(2);
        //充分運行線程LockSupportThread兩秒鐘后，中斷該線程，
        //該線程能從park()方法返回
        thread.interrupt();
        //LockSupport.unpark(thread);
    }

    static class LockSupportThread implements Runnable{
        @Override
        public void run() {
            LockSupport.park(); //阻塞自己
            System.out.println(Thread.currentThread().getName() + "從park()中返回");
        }
    }
}

它的應用在同步器AbstractQueueSynchronizer中有所體現，一個節點線程獲取不到鎖時，會阻塞自己，調用的就是LockSupport的park()方法，返回只有兩種方式，前一個節點線程釋放鎖時unpark()了當前節點；或者當前節點線程被中斷返回。

參考:

• 1. Java的LockSupport.park()實現分析