How to implement JAVA core thread pool principle analysis

How to implement JAVA core thread pool principle analysis

Introduction:
In actual Java development, thread pool is a very commonly used technology, it can Effectively manage and reuse threads to improve program performance and response speed. This article will introduce the principles of Java core thread pool and analyze it with specific code examples.

1. What is a thread pool?
The thread pool is a mechanism for managing threads. It can be used to create, start and manage multiple threads. Compared to creating a new thread every time a task needs to be executed, the thread pool makes full use of the reusability of threads and reduces the overhead of thread creation. The basic principle of the thread pool is to put the tasks that need to be executed into a task queue, and then execute the tasks through the threads in the thread pool.

2. Principle of JAVA core thread pool
The thread pool in Java is implemented through the ThreadPoolExecutor class. ThreadPoolExecutor is the default implementation of the ExecutorService interface, which implements the main logic and algorithms of the thread pool. Worker threads in the thread pool are executed by continuously taking tasks from the task queue.

Specifically, the principle of Java thread pool includes the following key points:

1. Core thread pool size, maximum thread pool size and task queue:
   Thread pool contains A thread pool size control parameter used to specify the size of the core thread pool. When a new task is submitted, the thread pool will create new worker threads based on the size of the core thread pool. When the task queue is full and the number of threads in the thread pool is less than the maximum thread pool size, new threads are created to execute the task. If the number of threads in the thread pool has reached the maximum thread pool size, new tasks submitted will be processed according to the set rejection policy.
2. Characteristics of the task queue:
   The task queue is a first-in, first-out queue used to store tasks to be executed. Java provides multiple types of task queues, such as: ArrayBlockingQueue, LinkedBlockingQueue, SynchronousQueue, etc. Different types of queues have different characteristics and usage scenarios. The specific queue to choose depends on the actual situation.
3. Expansion and contraction of the thread pool:
   When the task queue is full and the number of threads in the thread pool is less than the maximum thread pool size, the thread pool will create new threads to execute the task. When the number of threads in the thread pool exceeds the core thread pool size, and a thread exceeds the set maximum idle time (keepAliveTime), the thread pool will close the thread to reduce system resource usage.
4. Rejection policy:
   If the number of threads in the thread pool has reached the maximum thread pool size and the task queue is full, newly submitted tasks will be processed according to the set rejection policy. Commonly used rejection policies include: ThreadPoolExecutor.AbortPolicy (default policy, throws RejectedExecutionException exception), ThreadPoolExecutor.DiscardPolicy (abandons the latest task), and ThreadPoolExecutor.CallerRunsPolicy (returns the task to the caller to continue execution), etc.

3. Specific code examples
The following is a simple Java code example that demonstrates how to create and use a thread pool in Java:

import java.util.concurrent .ExecutorService;
import java.util.concurrent.Executors;

public class ThreadPoolExample {

public static void main(String[] args) {
    int corePoolSize = 5;
    
    ExecutorService executor = Executors.newFixedThreadPool(corePoolSize);
    
    for (int i = 0; i < 10; i++) {
        Runnable worker = new WorkerThread(String.valueOf(i));
        
        executor.execute(worker);
    }
    
    executor.shutdown();
    
    while (!executor.isTerminated()) {
        // 等待所有任务完成
    }
    
    System.out.println("所有任务已完成");
}

}

class WorkerThread implements Runnable {

private String threadName;

public WorkerThread(String threadName) {
    this.threadName = threadName;
}

@Override
public void run() {
    try {
        System.out.println(Thread.currentThread().getName() + " 开始执行任务 " + threadName);
        Thread.sleep(2000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println(Thread.currentThread().getName() + " 完成任务 " + threadName);
}

}

The above code creates and uses the thread pool through the ExecutorService interface and Executors factory class. When creating the thread pool, we specified the core thread pool size as 5 and created 10 tasks to execute in the thread pool. Each task is a WorkerThread object, and the specific logic of the task is defined by implementing the Runnable interface.

Conclusion:
This article mainly introduces the principle of Java core thread pool and analyzes it through specific code examples. Thread pool is a commonly used technology in multi-threaded programming, which can improve the performance and response speed of the program. In the actual development process, we can choose an appropriately sized thread pool and task queue according to the actual situation, and set an appropriate rejection policy to achieve optimal performance and resource utilization.

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