java 多线程 wait，notify

1. 因为涉及到对象锁，Wait、Notify一定要在synchronized里面进行使用。
2. Wait必须暂定当前正在执行的线程,并释放资源锁,让其他线程可以有机会运行
3. notify/notifyall: 唤醒线程

• 共享变量

public class ShareEntity {
    private String name;
    // 线程通讯标识
    private Boolean flag = false;

    public ShareEntity() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Boolean getFlag() {
        return flag;
    }

    public void setFlag(Boolean flag) {
        this.flag = flag;
    }
}

• 线程1（生产者）

public class CommunicationThread1 extends Thread{

    private ShareEntity shareEntity;
    public CommunicationThread1(ShareEntity shareEntity) {
        this.shareEntity = shareEntity;
    }

    @Override
    public void run() {
        int num = 0;
        while (true) {
            synchronized (shareEntity) {
                if (shareEntity.getFlag()) {
                    try {
                        shareEntity.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }

                if (num % 2 == 0)
                    shareEntity.setName("thread1-set-name-0");
                else
                    shareEntity.setName("thread1-set-name-1");
                num++;
                shareEntity.setFlag(true);
                shareEntity.notify();
            }
        }
    }
}

• 线程2（消费者）

public class CommunicationThread2 extends Thread{
    private ShareEntity shareEntity;
    public CommunicationThread2(ShareEntity shareEntity) {
        this.shareEntity = shareEntity;
    }

    @Override
    public void run() {
        while (true) {
            synchronized (shareEntity) {
                if (!shareEntity.getFlag()) {
                    try {
                        shareEntity.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println(shareEntity.getName());
                shareEntity.setFlag(false);
                shareEntity.notify();
            }
        }
    }
}

• 请求

@RequestMapping("test-communication")
    public void testCommunication() {
        ShareEntity shareEntity = new ShareEntity();
        CommunicationThread1 thread1 = new CommunicationThread1(shareEntity);
        CommunicationThread2 thread2 = new CommunicationThread2(shareEntity);
        thread1.start();
        thread2.start();
    }

• 结果

thread1-set-name-0
thread1-set-name-1
thread1-set-name-0
thread1-set-name-1
thread1-set-name-0
thread1-set-name-1
thread1-set-name-0