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  

1. import java.util.concurrent.locks.Condition;
2. import java.util.concurrent.locks.Lock;
3. import java.util.concurrent.locks.ReentrantLock;
4. //生产/消费者模式
5. public class Basket {
6. Lock lock = new ReentrantLock();
7. // 产生Condition对象
8. Condition produced = lock.newCondition();
9. Condition consumed = lock.newCondition();
10. boolean available = false;
11. public void produce() throws InterruptedException {
12. lock.lock();
13. try {
14. if (available) {
15. produced.await(); // 放弃lock进入睡眠
16. }
17. System.out.println("Apple produced.");
18. available = true;
19. consumed.signal(); // 发信号唤醒等待这个Condition的线程
20. } finally {
21. lock.unlock();
22. }
23. }
24. public void consume() throws InterruptedException {
25. lock.lock();
26. try {
27. if (!available) {
28. consumed.await(); // 放弃lock进入睡眠
29. }
30. /* 吃苹果 */
31. System.out.println("Apple consumed.");
32. available = false;
33. produced.signal(); // 发信号唤醒等待这个Condition的线程
34. } finally {
35. lock.unlock();
36. }
37. }
38. }

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  

1. import java.util.concurrent.ExecutorService;
2. import java.util.concurrent.Executors;
3. //测试用类
4. public class ConditionTester {
5. public static void main(String[] args) throws InterruptedException {
6. final Basket basket = new Basket();
7. // 定义一个producer
8. Runnable producer = new Runnable() {
9. public void run() {
10. try {
11. basket.produce();
12. } catch (InterruptedException ex) {
13. ex.printStackTrace();
14. }
15. }
16. };
17. // 定义一个consumer
18. Runnable consumer = new Runnable() {
19. public void run() {
20. try {
21. basket.consume();
22. } catch (InterruptedException ex) {
23. ex.printStackTrace();
24. }
25. }
26. };
27. // 各产生10个consumer和producer
28. ExecutorService service = Executors.newCachedThreadPool();
29. for (int i = 0; i < 4; i++)
30. service.submit(consumer);
31. Thread.sleep(2000 * 2);
32. for (int i = 0; i < 4; i++)
33. service.submit(producer);
34. service.shutdown();
35. }
36. }

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  

1. package com.sishuok.es.test;
2. import java.util.concurrent.atomic.AtomicInteger;
3. import java.util.concurrent.locks.Condition;
4. import java.util.concurrent.locks.Lock;
5. import java.util.concurrent.locks.ReentrantLock;
6. //生产/消费者模式
7. public class Basket {
8. Lock lock = new ReentrantLock(true);
9. // 产生Condition对象
10. Condition produced = lock.newCondition();
11. Condition consumed = lock.newCondition();
12. boolean available = false;
13. AtomicInteger producedAwaitCounter = new AtomicInteger(0);
14. public void produce() throws InterruptedException {
15. lock.lock();
16. try {
17. if (available || producedAwaitCounter.get() > 0) {
18. producedAwaitCounter.incrementAndGet();
19. produced.await(); // 放弃lock进入睡眠
20. producedAwaitCounter.decrementAndGet();
21. }
22. System.out.println("Apple produced.");
23. available = true;
24. consumed.signal(); // 发信号唤醒等待这个Condition的线程
25. } finally {
26. lock.unlock();
27. }
28. }
29. public void consume() throws InterruptedException {
30. lock.lock();
31. try {
32. if (!available) {
33. consumed.await(); // 放弃lock进入睡眠
34. }
35. /* 吃苹果 */
36. System.out.println("Apple consumed.");
37. available = false;
38. produced.signal(); // 发信号唤醒等待这个Condition的线程
39. } finally {
40. lock.unlock();
41. }
42. }
43. }

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();}}}