import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 有时候线程取得lock后需要在一定条件下才能做某些工作，比如说经典的Producer和Consumer问题。 在Java
* 5.0以前，这种功能是由Object类的wait(), notify()和notifyAll()等方法实现的，
* 在5.0里面，这些功能集中到了Condition这个接口来实现。
*/
public class ConditionTest {
/**
* 篮子程序。Consumer必须在篮子里有苹果的时候才能吃苹果，否则它必须暂时放弃对篮子的锁定，
* 等到Producer往篮子里放了苹果后再去拿来吃。而Producer必须等到篮子空了才能往里放苹果，
* 否则它也需要暂时解锁等Consumer把苹果吃了才能往篮子里放苹果。
*/
public static class Basket {
// 锁
Lock lock = new ReentrantLock();
// 根据锁产生Condition对象
Condition produced = lock .newCondition();
Condition consumed = lock .newCondition();
// 篮子中的苹果数
int num = 0;
// 篮子中的最多放的苹果数
int count = 5;
/**
* 生产苹果，往篮子里放
*
* @throws InterruptedException
*/
public void produce() throws InterruptedException {
// 获得锁
lock.lock();
System. out.println("Producer get a lock..." );
try {
// 判断是否满足生产条件
while (num == count) {
// 如果有苹果，则不生产，放弃锁，进入睡眠
// 等待消费者消费
System. out.println("Producer sleep..." );
consumed.await();
System. out.println("Producer awaked..." );
}
/* 生产苹果 */
Thread. sleep(new Random().nextInt(50));
System. out.println("Producer produced an Apple." );
num++;
System. out.println("Producer 篮子里有" + num + "个苹果" );
// 通知等待produced Condition的线程
produced.signal();
} finally {
lock.unlock();
}
}
/**
* 消费苹果，从篮子中取
*
* @throws InterruptedException
*/
public void consume() throws InterruptedException {
// 获得锁
lock.lock();
System. out.println("Consumer get a lock..." );
try {
// 判断是否满足消费条件
while (num == 0) {
// 如果没有苹果，无法消费，则放弃锁，进入睡眠
// 等待生产者生产苹果
System. out.println("Consumer sleep..." );
produced.await();
System. out.println("Consumer awaked..." );
}
/* 吃苹果 */
Thread. sleep(new Random().nextInt(500));
System. out.println("Consumer consumed an Apple." );
num--;
System. out.println("Consumer 篮子里剩" + num + "个苹果" );
// 发信号唤醒某个等待consumed Condition的线程
consumed.signal();
} finally {
lock.unlock();
}
}
}
/**
* 测试Basket程序
*/
public static void testBasket() throws Exception {
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 < 10; i++) {
service.execute(producer);
}
for (int i = 0; i < 10; i++) {
service.execute(consumer);
}
service.shutdown();
}
public static void main(String[] args) throws Exception {
ConditionTest. testBasket();
}
