多线程之ReentrantLock

package com.test2;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class Test2 {

	public static void main(String[] args) throws InterruptedException {  
        final ExecutorService exec = Executors.newFixedThreadPool(4);  
        final ReentrantLock lock = new ReentrantLock();  
        final Condition con = lock.newCondition();  
        final int time = 5;  
        final Runnable add = new Runnable() {  
          public void run() {  
            System.out.println("Pre " + lock);  
            lock.lock();  
            try {  
            
              con.await(time, TimeUnit.SECONDS);  
              
              //Thread.sleep(5000) ;
            } catch (InterruptedException e) {  
              e.printStackTrace();  
            } finally {  
              System.out.println("Post " + lock.toString());  
              lock.unlock();  
            }  
          }  
        };  
        
        /**
         * 开启测试线程：
         * 测试条件：四个线程占用同一把锁
         * 测试点：con.await与sleep的区别
         * 测试结果：await时
         * 这是它的输出：
				Pre ReentrantLock@a59698[Unlocked]
				Pre ReentrantLock@a59698[Unlocked]
				Pre ReentrantLock@a59698[Unlocked]
				Pre ReentrantLock@a59698[Unlocked]
				Post ReentrantLock@a59698[Locked by thread pool-1-thread-1]
				Post ReentrantLock@a59698[Locked by thread pool-1-thread-2]
				Post ReentrantLock@a59698[Locked by thread pool-1-thread-3]
				Post ReentrantLock@a59698[Locked by thread pool-1-thread-4]
				每一个线程的锁状态都是“Unlocked”,所以都可以运行。但在把con.await改成Thread.sleep(5000)时，输出就变成了：
				Pre ReentrantLock@a59698[Unlocked]
				Pre ReentrantLock@a59698[Locked by thread pool-1-thread-1]
				Pre ReentrantLock@a59698[Locked by thread pool-1-thread-1]
				Pre ReentrantLock@a59698[Locked by thread pool-1-thread-1]
				Post ReentrantLock@a59698[Locked by thread pool-1-thread-1]
				Post ReentrantLock@a59698[Locked by thread pool-1-thread-2]
				Post ReentrantLock@a59698[Locked by thread pool-1-thread-3]
				Post ReentrantLock@a59698[Locked by thread pool-1-thread-4]
         * 测试结论： 线程在等待时(con.await)，已经不在拥有（keep）该锁了，所以其他线程就可以获得重入锁了。
         */
        for(int index = 0; index < 4; index++) {
        	 exec.submit(add);  
        } 
         
        exec.shutdown();  
      }  
}