Java wait和notifyAll实现简单的阻塞队列

wait，会使调用的线程进入等待状态，会释放所持有的对象锁（调用的时候也必须先获取到锁，否则会抛出异常 IllegalMonitorStateException）

notifyAll、notify，会去唤醒应当前对象而等待的线程，（调用的时候也必须先获取到锁，否则会抛出异常 IllegalMonitorStateException）

顺便也记录一下join方法，调用join方法，会使当前线程进入等待，如果没有设置等待时间，就会等待另一个线程执行完成才返回（ps:调用join方法并不一定立刻执行另一个线程，只是当前线程进入等待，然后切换下一个线程）

import java.util.concurrent.atomic.AtomicInteger;

public class BlockQueue {
	
	private final Object addLock = new Object();
	
	private final Object deleteLock = new Object();
	
	private final Integer size = 30;
	
	private Object[] queue = new Object[size];
	
	private AtomicInteger count = new AtomicInteger(0);
	
	public void add(Object o) {
		//获取生产锁,wait方法必须获取到对象锁后才可以调用，否则抛出异常
		synchronized (addLock){
			//判断是否超过队列大小,超过则进入等待
			while (count.get() >= size){
				try {
					addLock.wait();
				}
				catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
			//存放一个
			queue[count.get()] = o;
			//递增
			int i = count.incrementAndGet();
			//打印一下日志
			String name = Thread.currentThread().getName();
			System.out.println(name + "生产了一个，现有数量" + i);
		}
		//如果队列有数据，则调用notifyAll唤醒消费者
		if (count.get() >= 1){
			//notifyAll、notify都需要先获取对象锁,否则会抛出异常
			synchronized (deleteLock){
				deleteLock.notifyAll();
			}
		}
	}
	
	public Object poll(){
		Object o;
		//先获取对象锁，和生产者类似
		synchronized (deleteLock){
			//队列里没有数据则等待
			while (count.get() <= 0){
				try {
					deleteLock.wait();
				}
				catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
			//获取数据
			o = queue[count.get()];
			//递减
			int i = count.decrementAndGet();
			String name = Thread.currentThread().getName();
			System.out.println(name + "消费了一个，现有数量" + i);
		}
		//如果队列没有满，则可以唤醒生产者
		if (count.get() < size){
			//需要先获取到锁
			synchronized (addLock){
				addLock.notifyAll();
			}
		}
		return o;
	}
	
	public static void main(String[] args) {
		BlockQueue blockQueue = new BlockQueue();
		Thread t1 = new Thread(()-> {
			while (true){
				blockQueue.add(new Object());
			}
		}
		);
		Thread t2 = new Thread(()-> {
			while (true){
				blockQueue.add(new Object());
			}
		}
		);
		Thread t3 = new Thread(()-> {
			while (true){
				blockQueue.add(new Object());
			}
		}
		);
		Thread t4 = new Thread(()-> {
			while (true){
				blockQueue.poll();
			}
		}
		);
		Thread t5 = new Thread(()-> {
			while (true){
				blockQueue.poll();
			}
		}
		);
		Thread t6 = new Thread(()-> {
			while (true){
				blockQueue.poll();
			}
		}
		);
		t1.start();
		t2.start();
		t3.start();
		t4.start();
		t5.start();
		t6.start();
	}
}

效果：其实这个递增递减操作和打印操作也不是原子操作

依次打印线程1,2,3

public class JoinTest {


 public static void main(String[] args) throws InterruptedException {
  Thread t1 = new Thread(() -> System.out.println(1));
  Thread t2 = new Thread(()-> System.out.println(2));
  Thread t3 = new Thread(()-> System.out.println(3));

  t1.start();
  t1.join();

  t2.start();
  t2.join();

  t3.start();
  t3.join();
 }
}

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