在并发控制的流程中,有一个很重要的概念,即为标题中的条件对象,条件对象对应的英文是Condition接口,我们使用ReentrantLock是,发现基于ReentrantLock可以获取到Contition接口,可以进行阻塞或者唤醒操作。本文从以下几个方面介绍。
Condition作用及用途
Condition是基于ReentrantLock使用的,我们使用Condition可以实现条件判断
Condition代码演示
演示代码1
演示Condition的基本用法,如下代码所示:
package com.yang.concurrent; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock; /** * 本实例测试Condition的基本用法 */ public class ConditionDemo1 { private ReentrantLock reentrantLock=new ReentrantLock(); private Condition condition=reentrantLock.newCondition(); public static void main(String[] args) { ConditionDemo1 conditionDemo1 = new ConditionDemo1(); new Thread(new Runnable() { @Override public void run() { try { Thread.sleep(1000); conditionDemo1.method2(); } catch (InterruptedException e) { e.printStackTrace(); } } }).start(); conditionDemo1.method1(); } public void method1(){ reentrantLock.lock(); try { System.out.println("条件不满足,等待中"); condition.await(); System.out.println("条件满足,可以运行"); } catch (InterruptedException e) { e.printStackTrace(); }finally { reentrantLock.unlock(); } } public void method2(){ reentrantLock.lock(); try{ condition.signal(); System.out.println("条件转换为满足"); }finally { reentrantLock.unlock(); } } }
运行结果如下:
演示代码2
本代码演示用Condition实现生产者和消费者,如下实例代码所示
package com.yang.concurrent; import java.util.PriorityQueue; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock; /** * 此实例我们用Condition去模拟生产者和消费者的实现 */ public class ConditionDemo2 { private int queueSize = 10; private PriorityQueue<Integer> queue = new PriorityQueue<Integer>(10); private ReentrantLock reentrantLock = new ReentrantLock(); private Condition notFull = reentrantLock.newCondition(); private Condition notEmpty = reentrantLock.newCondition(); public static void main(String[] args) { ConditionDemo2 conditionDemo2 = new ConditionDemo2(); Provider provider = conditionDemo2.new Provider(); Consumer consumer=conditionDemo2.new Consumer(); provider.start(); consumer.start(); } class Provider extends Thread { @Override public void run() { provid(); } private void provid() { while (true) { reentrantLock.lock(); try { //一直在生产 while (queue.size() == queueSize) { try { System.out.println("队列满了,等待中"); notFull.await(); } catch (InterruptedException e) { e.printStackTrace(); } } queue.offer(1); notEmpty.signalAll(); System.out.println("对列中放入了一个数据,队列大小为:" + queue.size()); } finally { reentrantLock.unlock(); } } } } class Consumer extends Thread { @Override public void run() { consume(); } private void consume() { try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } //一直在消费 while (true) { reentrantLock.lock(); try { while (queue.size() == 0) { //队列空 System.out.println("队列为空,等待中"); try { notEmpty.await(); } catch (InterruptedException e) { e.printStackTrace(); } } queue.poll(); notFull.signalAll(); System.out.println("从队列中取走了一个数据,队列剩余:" + queue.size()); } finally { reentrantLock.unlock(); } } } } }
运行结果如下图所示:
Condition使用说明
当我们调用await方法后,就释放了锁。