Condition
Condition 将 Object的通信方法（wait、notify 和 notifyAll）分解成截然不同的对象，以便通过将这些对象与任意 Lock 实现组合使用，为每个对象提供多个等待 set （wait-set）。其中，Lock 替代了 synchronized 方法和语句的使用，Condition 替代了 Object 通信方法的使用。
在Condition中，用await()替换wait()，用signal()替换notify()，用signalAll()替换notifyAll()，传统线程的通信方式，Condition都可以实现，这里注意，Condition是被绑定到Lock上的，要创建一个Lock的Condition必须用newCondition()方法。
Condition的强大之处在于它可以为多个线程间建立不同的Condition， 使用synchronized/wait()只有一个阻塞队列，notifyAll会唤起所有阻塞队列下的线程，而使用lock/condition，可以实现多个阻塞队列，signalAll只会唤起某个阻塞队列下的阻塞线程。
代码：
class Buffer {
private final Lock lock;
private final Condition notFull;
private final Condition notEmpty;
private int maxSize;
private List<Date> storage;
Buffer(int size){
//使用锁lock，并且创建两个condition，相当于两个阻塞队列
lock=new ReentrantLock();
notFull=lock.newCondition();
notEmpty=lock.newCondition();
maxSize=size;
storage=new LinkedList<>();
}
public void put() {
lock.lock();
try {
while (storage.size() ==maxSize ){//如果队列满了
System.out.print(Thread.currentThread().getName()+": wait \n");;
notFull.await();//阻塞生产线程
}
storage.add(new Date());
System.out.print(Thread.currentThread().getName()+": put:"+storage.size()+ "\n");
Thread.sleep(5000);
notEmpty.signalAll();//唤醒消费线程
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
lock.unlock();
}
}
public void take() {
lock.lock();
try {
while (storage.size() ==0 ){//如果队列满了
System.out.print(Thread.currentThread().getName()+": wait \n");;
notEmpty.await();//阻塞消费线程
}
System.out.print(Thread.currentThread().getName()+": take:"+storage.size()+ "\n");
Date d=((LinkedList<Date>)storage).poll();
Thread.sleep(5000);
notFull.signalAll();//唤醒生产线程
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
lock.unlock();
}
}
}
class Producer implements Runnable{
private Buffer buffer;
Producer(Buffer b){
buffer=b;
}
@Override
public void run() {
while(true){
buffer.put();
}
}
}
class Consumer implements Runnable{
private Buffer buffer;
Consumer(Buffer b){
buffer=b;
}
@Override
public void run() {
while(true){
buffer.take();
}
}
}
public class Main {
public static void main(String[] arg){
Buffer buffer=new Buffer(10);
Producer producer=new Producer(buffer);
Consumer consumer=new Consumer(buffer);
for(int i=0;i<3;i++){
new Thread(producer,"producer-"+i).start();
}
for(int i=0;i<3;i++){
new Thread(consumer,"consumer-"+i).start();
}
}
}
- 当生产者执行put方法时，调用notEmpty.signalAll()只会唤醒notEmpty.await()下的消费者线程。
- 当消费者执行take方法时，调用notFull.signalAll()只会唤醒notFull.await()下的消费者线程。
执行结果：
producer-0: put:1
producer-0: put:2
producer-0: put:3
producer-0: put:4
producer-0: put:5
producer-0: put:6
producer-0: put:7
producer-0: put:8
producer-0: put:9
producer-0: put:10
producer-0: wait
producer-1: wait
producer-2: wait
consumer-0: take:10
consumer-0: take:9
consumer-0: take:8
consumer-0: take:7
consumer-0: take:6
consumer-0: take:5
consumer-0: take:4
consumer-0: take:3
consumer-0: take:2
consumer-0: take:1
consumer-0: wait
consumer-1: wait
consumer-2: wait
producer-0: put:1
producer-0: put:2
producer-0: put:3
producer-0: put:4
producer-0: put:5
producer-0: put:6
producer-0: put:7
producer-0: put:8
producer-0: put:9
producer-0: put:10
producer-0: wait
producer-1: wait
producer-2: wait
consumer-0: take:10
consumer-0: take:9
consumer-0: take:8
consumer-0: take:7
consumer-0: take:6
consumer-0: take:5
consumer-0: take:4
consumer-0: take:3
consumer-0: take:2
consumer-0: take:1
consumer-0: wait
consumer-1: wait
consumer-2: wait
producer-0: put:1
producer-0: put:2
producer-0: put:3
producer-0: put:4
producer-0: put:5
producer-0: put:6
producer-0: put:7
producer-0: put:8
producer-1: put:9
完毕。
