package com.mgk.threads.shared;
import java.util.concurrent.Semaphore;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 共享锁
* Semaphore(int num)
* num 参数含义，允许多个线程共同运行。只有当之前的线程释放后，后续的线程还才可运行。
*
*/
public class TestThread {
public static void main(String[] args) {
Semaphore semaphore = new Semaphore(2);
Lock lock = new ReentrantLock();
new Thread( new ThreadA(semaphore,lock),"qx").start();
new Thread( new ThreadA(semaphore,lock),"sc").start();
new Thread( new ThreadA(semaphore,lock),"gk").start();
}
}
class ThreadA implements Runnable{
private volatile static int count = 2;
private Lock lock;
private Semaphore semaphore ;
public ThreadA(Semaphore semaphore, Lock lock){
this.semaphore = semaphore;
this.lock=lock;
}
private int get(){
this.lock.lock();
try {
return --count;
}finally {
this.lock.unlock();
}
}
private int exit(){
this.lock.lock();
try {
return ++count;
}finally {
this.lock.unlock();
}
}
@Override
public void run() {
try {
this.semaphore.acquire();
System.out.println(Thread.currentThread().getName() +"进入停车厂，剩余车位：" + get());
Thread.sleep(2000);
System.out.println(Thread.currentThread().getName() +"出入停车厂，剩余车位：" + exit());
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
semaphore.release();
}
}
}
停车场就两个停车位 也就是只能允许两个线程进去然后争夺锁钥匙停车 当有车出去后，空出停车场位置，下一辆车才允许进来
如果不释放锁会一直阻塞状态
