阻塞队列以及原子操作等并发工具

先来一个案列,了解Condition

生产者

public class Producer implements Runnable{

    private Queue<String> msg;
    private int maxSize;
    Lock lock;
    Condition condition;

    public Producer(Queue<String> msg, int maxSize, Lock lock, Condition condition) {
        this.msg = msg;
        this.maxSize = maxSize;
        this.lock = lock;
        this.condition = condition;
    }

    @Override
    public void run() {
        int i=0;
        while(true){
            i++;
            lock.lock();
                while(msg.size()==maxSize){
                    System.out.println("生产者队列满了，先等待");
                    try {
                        condition.await(); //阻塞当前线程并释放锁进行等
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("生产消息："+i);
                msg.add("生产者的消息内容"+i);
                condition.signal(); //唤醒阻塞状态下的线程
            lock.unlock();
        }
    }
    
}

消费者

public class Consumer implements Runnable{
    
    private Queue<String> msg;
    private int maxSize;
    Lock lock;
    Condition condition;

    public Consumer(Queue<String> msg, int maxSize, Lock lock, Condition condition) {
        this.msg = msg;
        this.maxSize = maxSize;
        this.lock = lock;
        this.condition = condition;
    }

    @Override
    public void run() {
        int i=0;
        while(true){
            i++;
            lock.lock(); //synchronized
            while(msg.isEmpty()){
                System.out.println("消费者队列空了，先等待");
                try {
                    condition.await(); //阻塞当前线程并释放锁进行等待
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("消费消息："+msg.remove());
            condition.signal(); //唤醒阻塞状态下的线程
            lock.unlock();
        }
    }
    
}

测试

public class Test 
{
    public static void main( String[] args )
    {
        Queue<String> queue=new LinkedList<>();
        Lock lock=new ReentrantLock(); //重入锁
        Condition condition=lock.newCondition();
        int maxSize=5;

        Producer producer=new Producer(queue,maxSize,lock,condition);
        Consumer consumer=new Consumer(queue,maxSize,lock,condition);

        Thread t1=new Thread(producer);
        Thread t2=new Thread(consumer);
        t1.start();
        t2.start();
    }
    
}

控制台输出：

原理分析

public final void await() throws InterruptedException {
            if (Thread.interrupted())
                throw new InterruptedException();
            Node node = addConditionWaiter();
            int savedState = fullyRelease(node);
            int interruptMode = 0;
            while (!isOnSyncQueue(node)) {
                LockSupport.park(this);
                if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
                    break;
            }
            if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
                interruptMode = REINTERRUPT;
            if (node.nextWaiter != null) // clean up if cancelled
                unlinkCancelledWaiters();
            if (interruptMode != 0)
                reportInterruptAfterWait(interruptMode);
}
private Node addConditionWaiter() {
            Node t = lastWaiter;  //最后一个等待节点
            // If lastWaiter is cancelled, clean out.
            if (t != null && t.waitStatus != Node.CONDITION) {
                unlinkCancelledWaiters();
                t = lastWaiter;
            }
            Node node = new Node(Thread.currentThread(), Node.CONDITION); //把当前获得锁的线程构建成一个node
            if (t == null)
                firstWaiter = node;
            else
                t.nextWaiter = node;
            lastWaiter = node;
            return node;
}