wait/notify/notifyall

wait和notify 等待和唤醒 ， 需要包围在synchronized里，当获取到同一把锁，notify就能唤醒wait

 

1. wait和notify使用：

当只调用wait，不调用notify，

public class TestWaitNotify {
    public static void main(String[] args) {

        Object object = new Object();
        Thread t1 = new Thread(() -> doWait(object));
        t1.start();

//        Thread t2 = new Thread(() -> doNotify(object));
//        t2.start();
    }

    public static void doWait(Object object) {
        synchronized (object) {
            try {
                System.out.println("wait....");
                object.wait();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void doNotify(Object object) {
        synchronized (object) {
            System.out.println("notify...");
            object.notify();
        }
    }
}

 会一直等待状态

 

当调用了wait，又用同一个锁（object ）调用notify, 

public class TestWaitNotify {
    public static void main(String[] args) {

        Object object = new Object();
        Thread t1 = new Thread(() -> doWait(object));
        t1.start();

        Thread t2 = new Thread(() -> doNotify(object));
        t2.start();
    }

    public static void doWait(Object object) {
        synchronized (object) {
            try {
                System.out.println("wait....");
                object.wait();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void doNotify(Object object) {
        synchronized (object) {
            System.out.println("notify...");
            object.notify();
        }
    }
}

 就能执行完并且释放锁。

 

 

2. notify和notifyall

看下面一个例子：

public class TestWaitNotify {
    public static void main(String[] args) {

        Object object = new Object();
        for (int i = 0; i < 5; i++) {
            Thread t1 = new Thread(() -> doWait(object));
            t1.start();
        }
        
        Thread t2 = new Thread(() -> doNotify(object));
        t2.start();
    }

    public static void doWait(Object object) {
        synchronized (object) {
            try {
                System.out.println("wait....");
                object.wait();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void doNotify(Object object) {
        synchronized (object) {
            System.out.println("notify...");
            object.notify();
        }
    }
}

 启动了五个线程，但是notify只会唤醒一个，其余的都还在等待。

public class TestWaitNotify {
    public static void main(String[] args) {

        Object object = new Object();
        for (int i = 0; i < 5; i++) {
            Thread t1 = new Thread(() -> doWait(object));
            t1.start();
        }

        Thread t2 = new Thread(() -> doNotifyAll(object));
        t2.start();
    }

    public static void doWait(Object object) {
        synchronized (object) {
            try {
                System.out.println("wait....");
                object.wait();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static void doNotify(Object object) {
        synchronized (object) {
            System.out.println("notify...");
            object.notify();
        }
    }

    public static void doNotifyAll(Object object) {
        synchronized (object) {
            System.out.println("notify all...");
            object.notifyAll();
        }
    }
}

 使用notifyall，会一次性唤醒所有线程。