作者要的是一个生产者生成，接着必须有一个消费者消费，那这不是需要单线程吗？或者使用1个大小的阻塞队列。所以只谈论问题本身，不谈论好不好。
具体代码：
Java代码 
- import java.util.concurrent.locks.Condition;
- import java.util.concurrent.locks.Lock;
- import java.util.concurrent.locks.ReentrantLock;
- //生产/消费者模式
- public class Basket {
- Lock lock = new ReentrantLock();
- // 产生Condition对象
- Condition produced = lock.newCondition();
- Condition consumed = lock.newCondition();
- boolean available = false;
- public void produce() throws InterruptedException {
- lock.lock();
- try {
- if (available) {
- produced.await(); // 放弃lock进入睡眠
- }
- System.out.println("Apple produced.");
- available = true;
- consumed.signal(); // 发信号唤醒等待这个Condition的线程
- } finally {
- lock.unlock();
- }
- }
- public void consume() throws InterruptedException {
- lock.lock();
- try {
- if (!available) {
- consumed.await(); // 放弃lock进入睡眠
- }
- /* 吃苹果 */
- System.out.println("Apple consumed.");
- available = false;
- produced.signal(); // 发信号唤醒等待这个Condition的线程
- } finally {
- lock.unlock();
- }
- }
- }
import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;//生产/消费者模式public class Basket {Lock lock = new ReentrantLock();// 产生Condition对象Condition produced = lock.newCondition();Condition consumed = lock.newCondition();boolean available = false;public void produce() throws InterruptedException {lock.lock();try {if (available) {produced.await(); // 放弃lock进入睡眠}System.out.println("Apple produced.");available = true;consumed.signal(); // 发信号唤醒等待这个Condition的线程} finally {lock.unlock();}}public void consume() throws InterruptedException {lock.lock();try {if (!available) {consumed.await(); // 放弃lock进入睡眠}/* 吃苹果 */System.out.println("Apple consumed.");available = false;produced.signal(); // 发信号唤醒等待这个Condition的线程} finally {lock.unlock();}}}
Java代码
- import java.util.concurrent.ExecutorService;
- import java.util.concurrent.Executors;
- //测试用类
- public class ConditionTester {
- public static void main(String[] args) throws InterruptedException {
- final Basket basket = new Basket();
- // 定义一个producer
- Runnable producer = new Runnable() {
- public void run() {
- try {
- basket.produce();
- } catch (InterruptedException ex) {
- ex.printStackTrace();
- }
- }
- };
- // 定义一个consumer
- Runnable consumer = new Runnable() {
- public void run() {
- try {
- basket.consume();
- } catch (InterruptedException ex) {
- ex.printStackTrace();
- }
- }
- };
- // 各产生10个consumer和producer
- ExecutorService service = Executors.newCachedThreadPool();
- for (int i = 0; i < 4; i++)
- service.submit(consumer);
- Thread.sleep(2000 * 2);
- for (int i = 0; i < 4; i++)
- service.submit(producer);
- service.shutdown();
- }
- }
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;//测试用类
public class ConditionTester {public static void main(String[] args) throws InterruptedException {final Basket basket = new Basket();// 定义一个producerRunnable producer = new Runnable() {public void run() {try {basket.produce();} catch (InterruptedException ex) {ex.printStackTrace();}}};// 定义一个consumerRunnable consumer = new Runnable() {public void run() {try {basket.consume();} catch (InterruptedException ex) {ex.printStackTrace();}}};// 各产生10个consumer和producerExecutorService service = Executors.newCachedThreadPool();for (int i = 0; i < 4; i++)service.submit(consumer);Thread.sleep(2000 * 2);for (int i = 0; i < 4; i++)service.submit(producer);service.shutdown();}
}
原因分析：
1、假设前面有2个producer(此时available=true)
1.1、一个在等待lock
1.2、一个await
2、consumer生成内容后，available=false，produced.signal(); 最后lock.unlock();
3.1、因为lock.unlock所以会触发一个lock获取到锁（虽然signal也会触发等待这个条件的其他线程，但是多线程大家都知道什么时候触发这是不确定的），如果此时正好是[1.1]那么因为available=false，执行完释放锁
3.2、produced.signal()所以会触发一个await的producer；
解决方案：
只要保证[3.1]还是需要await即可解决问题
所以加一个 AtomicInteger producedAwaitCounter = new AtomicInteger(0); 统计当前等待的生产者，如果当前available=false，但已经有生产者生成了内容，那么先等待消费者消费了再说
if (available || producedAwaitCounter.get() > 0) {
producedAwaitCounter.incrementAndGet();
produced.await(); // 放弃lock进入睡眠
producedAwaitCounter.decrementAndGet();
}
当然最简单的是使用：自旋，原理可以自己分析下：
while (available) {
produced.await(); // 放弃lock进入睡眠
}
Java代码
- package com.sishuok.es.test;
- import java.util.concurrent.atomic.AtomicInteger;
- import java.util.concurrent.locks.Condition;
- import java.util.concurrent.locks.Lock;
- import java.util.concurrent.locks.ReentrantLock;
- //生产/消费者模式
- public class Basket {
- Lock lock = new ReentrantLock(true);
- // 产生Condition对象
- Condition produced = lock.newCondition();
- Condition consumed = lock.newCondition();
- boolean available = false;
- AtomicInteger producedAwaitCounter = new AtomicInteger(0);
- public void produce() throws InterruptedException {
- lock.lock();
- try {
- if (available || producedAwaitCounter.get() > 0) {
- producedAwaitCounter.incrementAndGet();
- produced.await(); // 放弃lock进入睡眠
- producedAwaitCounter.decrementAndGet();
- }
- System.out.println("Apple produced.");
- available = true;
- consumed.signal(); // 发信号唤醒等待这个Condition的线程
- } finally {
- lock.unlock();
- }
- }
- public void consume() throws InterruptedException {
- lock.lock();
- try {
- if (!available) {
- consumed.await(); // 放弃lock进入睡眠
- }
- /* 吃苹果 */
- System.out.println("Apple consumed.");
- available = false;
- produced.signal(); // 发信号唤醒等待这个Condition的线程
- } finally {
- lock.unlock();
- }
- }
- }
package com.sishuok.es.test;import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;//生产/消费者模式public class Basket {Lock lock = new ReentrantLock(true);// 产生Condition对象Condition produced = lock.newCondition();Condition consumed = lock.newCondition();boolean available = false;AtomicInteger producedAwaitCounter = new AtomicInteger(0);public void produce() throws InterruptedException {lock.lock();try {if (available || producedAwaitCounter.get() > 0) {producedAwaitCounter.incrementAndGet();produced.await(); // 放弃lock进入睡眠producedAwaitCounter.decrementAndGet();}System.out.println("Apple produced.");available = true;consumed.signal(); // 发信号唤醒等待这个Condition的线程} finally {lock.unlock();}}public void consume() throws InterruptedException {lock.lock();try {if (!available) {consumed.await(); // 放弃lock进入睡眠}/* 吃苹果 */System.out.println("Apple consumed.");available = false;produced.signal(); // 发信号唤醒等待这个Condition的线程} finally {lock.unlock();}}}
