In-depth understanding of Java multi-threaded programming: advanced application of wait and notify methods

Multi-threaded programming in Java: Master the advanced usage of wait and notify

Introduction:
Multi-threaded programming is a common technology in Java development. Faced with For complex business processing and performance optimization requirements, rational use of multi-threading can greatly improve the running efficiency of the program. In multi-threaded programming, wait and notify are two important keywords used to achieve coordination and communication between threads. This article will introduce the advanced usage of wait and notify and provide specific code examples to help readers better understand and apply this technology.

1. Basic concepts and usage of wait and notify
In multi-thread programming, wait and notify are two important methods defined in the Object class. They are used to realize thread waiting and waking up. When a thread enters the waiting state by calling the wait method, it will release the object's lock and wait for other threads to wake up through the notify or notifyAll method. When a thread calls the notify or notifyAll method, it will wake up one or all threads waiting for the object.

The basic usage of wait and notify is as follows:

• Before calling the wait method, you must first obtain the lock of the object, that is, call the wait method in the synchronized code block.
• After calling the wait method, the current thread will release the object's lock and enter the waiting state.
• After calling the notify method, a thread waiting for the object will be awakened and put into the ready state.
• After calling the notifyAll method, all threads waiting for the object will be awakened and put into the ready state.

2. Advanced usage of wait and notify
In addition to the basic waiting and wake-up functions, wait and notify can also perform some advanced usage, such as: waiting for timeout, interrupt, etc. These advanced usages are introduced below through specific code examples.

1. Waiting timeout
   When using the wait method of the Object class, you can set a waiting timeout. If it is not awakened within the timeout period, it will automatically wake up. The sample code is as follows:

synchronized (obj) {
    try {
        obj.wait(5000); // 等待5秒钟
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

2. Interrupt waiting
   When in the waiting state, the thread can be awakened in advance through the interrupt operation. The sample code is as follows:

synchronized (obj) {
    try {
        obj.wait(); // 等待被唤醒
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

// 主线程中调用interrupt方法中断等待的线程
thread.interrupt();

3. Thread coordination through condition variables
   When multiple threads are waiting for a condition to be met at the same time, you can use condition variables (Condition) for thread coordination. The sample code is as follows:

Lock lock = new ReentrantLock();
Condition condition = lock.newCondition();

// 等待条件满足
lock.lock();
try {
    while (!conditionSatisfied) {
        condition.await(); // 等待条件满足
    }
} catch (InterruptedException e) {
    e.printStackTrace();
} finally {
    lock.unlock();
}

// 唤醒等待的线程
lock.lock();
try {
    condition.signal(); // 唤醒等待的线程
} finally {
    lock.unlock();
}

3. Summary
This article introduces the advanced usage of wait and notify in multi-threaded programming in Java. Mastering these advanced usages allows you to more flexibly utilize multi-threading for business processing and performance optimization. In actual development, appropriate wait timeouts, interruptions and other operations must be selected according to needs to ensure normal multi-thread coordination and communication. At the same time, attention should also be paid to thread safety and the use of locks to avoid problems such as race conditions. I hope this article will be helpful to readers in their learning and practice of multi-threaded programming.

Reference materials:

• Java API Documentation
• https://www.cnblogs.com/dolphin0520/p/3920397.html

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