java里面的Synchronizers-Latch,Barrier,Se地图hore,ReentrantLock,Condtion

java里面的Synchronizers--Latch,Barrier,Semaphore,ReentrantLock,Condtion

昨晚闲来翻了一会Java ConcurrentCy in Practise,

进一步明确了java 一些 Synchronizers的用法，在此简单记录一下

昨日随手写的demo代码。只是为了加深印象，所以不怎么讲究，如有看官路过请不要挑剔：

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import java.util.concurrent.BrokenBarrierException;import java.util.concurrent.CountDownLatch;import java.util.concurrent.CyclicBarrier;import java.util.concurrent.Semaphore;import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.ReentrantLock;public class NightDinner {private Semaphore sem=new Semaphore(3);private CountDownLatch startLatch=new CountDownLatch(1);private CountDownLatch latch=new CountDownLatch(4);private CyclicBarrier barrier=new CyclicBarrier(2,new Runnable(){public void run() {System.out.println("barrier tripped");}});    private ReentrantLock lock=new ReentrantLock();    private Condition condition=lock.newCondition();public static void main(String[] args) {NightDinner nd=new NightDinner();nd.testLatch();nd.testBarrier();nd.testLock();nd.testSemaphore();}public void testLatch(){for(int i=0;i<4;i++){new Thread(new AThread()).start();}startLatch.countDown();System.out.println("latch begin");try {latch.await();} catch (InterruptedException e) {e.printStackTrace();}System.out.println("latch zero reached");}public void testBarrier(){for(int i=0;i<2;i++){new Thread(new BThread()).start();}}public void testLock(){for(int i=0;i<3;i++)new Thread(new CThread()).start();try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}lock.lock();//condition.signal();condition.signalAll();//要显式地释放掉lock的锁lock.unlock();}public void testSemaphore(){for(int i=0;i<4;i++)new Thread(new DThread()).start();}public class AThread implements Runnable{public void run() {try {startLatch.await();} catch (InterruptedException e) {} latch.countDown(); System.out.println("latch down1");}}public class BThread implements Runnable{public void run() {try {System.out.println("barrier begints to await");barrier.await();} catch (InterruptedException e) {e.printStackTrace();} catch (BrokenBarrierException e) {e.printStackTrace();}}}public class CThread implements Runnable{public void run() {         lock.lock();         try {         System.out.println("lock got.conditon begins to wait");//condition的wait方法将release当前线程持有的condtion相关的lock的锁，然后等待被唤醒         condition.await();} catch (InterruptedException e) {e.printStackTrace();}finally{System.out.println("conditon signaled");lock.unlock();}}}public class DThread implements Runnable{public void run() {boolean suc=sem.tryAcquire();System.out.println("sem result:"+suc);}}}

?? 总结一下，就是：

?? CountdownLatch:

?? 一个主人线程一直await,知道所有客人线程都countdown并且latch的值为0，那么

?? 主人认为时机已成熟，开饭。

?? CyclicBarrier:

?? 一桌有10个位子，人不满不能开席(定义cyclicbarrier的时候可选的runnable行为)。于是，来了一个(await),又来了一个...第10个来了，barrier发现时机已成熟，开饭。

?? Semapore:

?? 一桌有10个位子。来了一个(acquire)..第10个来了....第11个来了....哈哈，没有位子了，站着吧

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? ReentrantLock:

? 这个官方文档可能读起来不是很顺畅，还是通过代码明白得更深入一些。

? 一个lock可以有多个Condtion。每个Condtion都有一个管理的lock。

? Conditon可以await(释放掉关联的Lock的锁,等待notif),也可以notify(通知其他线程处于condtion await 状态的线程可以做好继续获取lock的锁的准备了。notify之后要显式地释放掉lock锁).

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