java - 关于线程的wait()/notify

Question

我试图写一个关于如何使用wait()和notify()的示例，但是似乎无法通知wait()

public class Transfer {
    private int[] data;
    private volatile int ptr;
    private final Object lock = new Object();

    public Transfer(int[] data) {
        this.data = data;
        this.ptr = 0;
    }

    public void send() {
        while (ptr < data.length) {
            synchronized (lock) {
                try {
                    System.out.println("-----wait");
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                ptr++;
            }
        }
    }

    public void receive() {
        while (ptr < data.length) {
            synchronized (lock) {
                System.out.println("current is " + data[ptr]);
                System.out.println("-----notify");
                lock.notifyAll();
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        }
    }

}

////in main()

       int[] data = new int[] { 111, 222, 333, 444, 555, 666, 777, 888, 999, 000 };
        Transfer tf = new Transfer(data);
        Thread t1 = new Thread(() -> {
            tf.receive();
        });
        Thread t2 = new Thread(() -> {
            tf.send();
        });
        t2.start();
        t1.start();

但结果是:
- - -等待
当前是111
- - -通知
当前是111
- - -通知
[无尽重复]
这不是我所期望的，应该是:
当前是111
当前是222 ...

Answer 1

class Transfer {
            private int[] data;
            private volatile int ptr;
            private final Object lock = new Object();

            public Transfer(int[] data) {
                this.data = data;
                this.ptr = 0;
            }

            public void send() {
                while (ptr < data.length) {
                    synchronized (lock) {
                        try {
                            System.out.println("-----wait");
                            lock.notifyAll();
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        ptr++;
                    }
                }
            }

            public void receive() {
                while (ptr < data.length) {
                    synchronized (lock) {
                        System.out.println("current is " + data[ptr]);
                        System.out.println("-----notify");
                        try {
                            lock.notifyAll();
                            lock.wait();
                            Thread.sleep(1000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }

                }
            }

        }

“Thread.sleep”不会释放锁定。因此，您需要“lock.wait”来释放该锁并让其他线程继续进行。然后，在“发送”增加指针后，它还应该发出通知，以便其他继续阻塞接收的线程现在可以继续进行。