Java并发Semaphore信号量的学习

public class MyThreadTest {private final static Semaphore semaphore = new Semaphore(2);// 设置2个车位public static void main(String[] args) {System.out.println("start");p(semaphore, true, 1);p(semaphore, false, 2);p(semaphore, false, 3);p(semaphore, true, 4);p(semaphore, true, 5);System.out.println("end");}/*** 停车** @param semaphore 信号对象* @param enterInto 停车true/出库false* @param theCarNum 车辆序号*/private static void p(Semaphore semaphore, boolean enterInto, int theCarNum) {if (!enterInto) {try {Thread.sleep(2000);} catch (Exception e) {e.printStackTrace();}System.out.println("车辆出库");// 释放1个车位// 通过LockSupport.unpark(s.thread)来释放锁，详见AbstractOwnableSynchronizer.unparkSuccessorsemaphore.release(1);}try {// 如果达到设定的信号量，通过LockSupport.park(this)来释放锁，详见AbstractOwnableSynchronizer.parkAndCheckInterruptsemaphore.acquire();System.out.println("第 " + theCarNum + " 辆车进入");} catch (Exception e) {e.printStackTrace();}}/***     Semaphore中Sync继承了AbstractQueuedSynchronizer*     改变AbstractOwnableSynchronizer中state值（该值记录着剩余信号量）**     AbstractOwnableSynchronizer加载时会调用静态代码块获取state的偏移地址：*     stateOffset = unsafe.objectFieldOffset(AbstractQueuedSynchronizer.class.getDeclaredField("state"));*     上述获取对象某个变量的效率比使用反射获取的效率高**     protected final boolean compareAndSetState(int expect, int update) {*          // stateOffset为state变量的偏移地址*         return unsafe.compareAndSwapInt(this, stateOffset, expect, update);*     }*/}

　　

原文：https://blog.csdn.net/qq_35001776/article/details/89158734