/**

* Unblock the given thread blocked on <tt>park</tt>, or, if it is

* not blocked, cause the subsequent call to <tt>park</tt> not to

* block. Note: this operation is "unsafe" solely because the

* caller must somehow ensure that the thread has not been

* destroyed. Nothing special is usually required to ensure this

* when called from Java (in which there will ordinarily be a live

* reference to the thread) but this is not nearly-automatically

* so when calling from native code.

* @param thread the thread to unpark.

*

*/

public native void unpark(Object thread);

park方法用于Block current thread。在以下情况下返回

1 针对当前线程已经调用过unpark(多次调用unpark的效果和调用一次unpark的效果一样)

 

public static void main(String[] args) throws Exception {              Unsafe unsafe = UnsafeUtil.getUnsafe();              Thread currThread = Thread.currentThread();            unsafe.unpark(currThread);      unsafe.unpark(currThread);      unsafe.unpark(currThread);            unsafe.park(false, 0);            System.out.println("SUCCESS!!!");    }

 

park方法马上返回

2 在当前线程中断的时候或者调用unpark的时候

  

public static void main(String[] args) throws Exception {              Unsafe unsafe = UnsafeUtil.getUnsafe();              Thread currThread = Thread.currentThread();      new Thread(()->{          try {            Thread.sleep(3000);            currThread.interrupt();            //unsafe.unpark(currThread);        } catch (Exception e) {}      }).start();            unsafe.park(false, 0);            System.out.println("SUCCESS!!!");    }

 

　park在3秒后返回

3 如果是相对时间也就是isAbsolute为false（注意这里后面的单位纳秒）到期的时候

public static void main(String[] args) throws Exception {              Unsafe unsafe = UnsafeUtil.getUnsafe();      //相对时间后面的参数单位是纳秒      unsafe.park(false, 3000000000l);            System.out.println("SUCCESS!!!");    }

 

　3秒后 park返回

4 如果是绝对时间也就是isAbsolute为true(注意后面的单位是毫秒)到期的时候

public static void main(String[] args) throws Exception {              Unsafe unsafe = UnsafeUtil.getUnsafe();            long time = System.currentTimeMillis()+3000;            //绝对时间后面的参数单位是毫秒      unsafe.park(true, time);            System.out.println("SUCCESS!!!");    }

3秒后 park返回

5 无理由的返回

 

unpark方法最好不要在调用park前对当前线程调用unpark

/**     * Unblock the given thread blocked on park, or, if it is     * not blocked, cause the subsequent call to park not to     * block.  Note: this operation is "unsafe" solely because the     * caller must somehow ensure that the thread has not been     * destroyed. Nothing special is usually required to ensure this     * when called from Java (in which there will ordinarily be a live     * reference to the thread) but this is not nearly-automatically     * so when calling from native code.     * @param thread the thread to unpark.     *     */    public native void unpark(Object thread);