In-depth discussion of practical application cases of wait and notify in Java: Detailed explanation of inter-thread communication

Inter-thread communication in Java: Detailed explanation of the practical application scenarios of wait and notify

In multi-thread programming, communication between threads is an important technology. Java provides two basic methods of inter-thread communication, namely using the wait and notify methods of objects. This article will analyze the actual application scenarios of wait and notify in detail and give specific code examples.

1. Introduction

In multi-threaded programming, communication between threads refers to the cooperation between multiple threads to complete specific tasks. Threads often need to share variables, data, or resources, and a mechanism is needed to ensure synchronization and order. Java provides a way to implement inter-thread communication based on object monitors, that is, using the wait and notify methods of the object.

2. Introduction to wait and notify methods

The wait method is a method in the Object class, which puts the current thread into a waiting state and releases the object's lock. This method needs to be called in a synchronized code block or synchronized method, and can only be called by the thread holding the object lock. The wait method is usually used in conjunction with the notify method to implement the thread's waiting and waking up mechanism.

The notify method is a method in the Object class, which is used to wake up waiting threads. The notify method needs to be called in a synchronized code block or synchronized method, and can only be called by the thread holding the object lock. The notify method randomly wakes up a waiting thread and puts it into the ready state.

3. Practical application scenarios of wait and notify

The following are several common usage scenarios, showing how to use the wait and notify methods to achieve inter-thread communication.

3.1 Producer-Consumer Model

The producer-consumer model is a classic thread synchronization problem, in which one or more threads act as producers, generate data, and Put it into the shared buffer; one or more threads act as consumers, take the data out of the buffer and process it. Under this model, communication is required between producers and consumers to ensure that producers wait when the buffer is full and consumers wait when the buffer is empty.

The following is a simple example that demonstrates how to use the wait and notify methods to implement the producer-consumer model:

public class ProducerConsumerExample {
    private List<Integer> buffer = new ArrayList<>();
    private int maxSize = 5;

    public synchronized void produce() throws InterruptedException {
        while (buffer.size() == maxSize) {
            wait();
        }

        Random random = new Random();
        int value = random.nextInt(100);
        buffer.add(value);
        System.out.println("Produced: " + value);

        notifyAll();
    }

    public synchronized void consume() throws InterruptedException {
        while (buffer.size() == 0) {
            wait();
        }

        int value = buffer.remove(0);
        System.out.println("Consumed: " + value);

        notifyAll();
    }
}

In this example, the ProducerConsumerExample class implements the producer and consumer logic. In the produce method, if the buffer is full, the thread enters the waiting state (calling the wait method) until a consumer consumes data and calls the notifyAll method to wake up the waiting producer thread. Similarly, in the consume method, if the buffer is empty, the thread enters the waiting state until a producer produces data and calls the notifyAll method to wake up the waiting consumer thread.

3.2 Thread collaboration

Sometimes, multiple threads need to be executed in a specific order. After one thread completes a specific task, it needs to notify the next thread to continue execution. In this scenario, you can also use the wait and notify methods to achieve thread collaboration.

The following is a simple example that demonstrates how to use the wait and notify methods to achieve thread collaboration:

public class ThreadCooperationExample {
    private boolean isTask1Completed = false;

    public synchronized void task1() throws InterruptedException {
        while (!isTask1Completed) {
            wait();
        }

        System.out.println("Task 1 completed");
    }

    public synchronized void task2() {
        System.out.println("Task 2 started");

        // 执行任务2的代码

        isTask1Completed = true;
        notify();
    }
}

In this example, the ThreadCooperationExample class implements two tasks task1 and task2. In task1, the thread will continuously check the status of isTask1Completed. If it is false, it will enter the waiting state (call the wait method) until task2 sets isTask1Completed to true and then calls the notify method to wake up the waiting task1 thread.

4. Summary

This article introduces the practical application scenarios of wait and notify methods in detail, and gives specific code examples. As we can see, the wait and notify methods can realize communication and cooperation between threads in multi-threaded programming, ensuring the order and synchronization of threads. In actual development, according to different needs, we can flexibly use the wait and notify methods to write efficient and reliable multi-threaded applications.

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