How does Java create and manage thread pools?

Thread pool is a pre-created collection of threads used to perform concurrent tasks. It can optimize thread usage, improve performance and prevent resource exhaustion. Specific usage methods include: using the Executors class to create a thread pool. Submit tasks using the submit() method. Use shutdown() to shut down the thread pool and wait for the task to complete. Use shutdownNow() to immediately terminate the thread pool and interrupt running tasks.

Java Thread Pool Creation and Management Guide

Introduction

The thread pool is A set of pre-created threads that can be used to perform concurrent tasks. It provides a mechanism to manage and optimize thread usage, improving performance and preventing resource exhaustion.

Create a thread pool

Use the Executors class to create a thread pool:

ExecutorService threadPool = Executors.newFixedThreadPool(numThreads);

where numThreads is The number of threads to create.

Manage Thread Pool

Once the thread pool is created, you can manage it using the following methods:

• Submit the task: Use submit() method to submit the task:

  Future<Result> future = threadPool.submit(task);

• Close the thread pool: Use shutdown() Method to shut down the thread pool, it will wait for all running tasks to complete:

  threadPool.shutdown();

• Terminate the thread pool: Use shutdownNow() Method to terminate the thread pool immediately, it will try to interrupt all running tasks:

  threadPool.shutdownNow();

Practical case

The following code demonstrates how to use The thread pool handles image processing tasks:

ExecutorService threadPool = Executors.newFixedThreadPool(4);
List<Image> images = ...;  // 获取需处理的图像列表

for (Image image : images) {
    Future<Image> future = threadPool.submit(() -> processImage(image));
}

// 等待所有图像处理完成
for (Future<Image> future : futures) {
    Image processedImage = future.get();
}

In this example, the thread pool processes up to 4 images at the same time. When submitting a task, the submit() method will return a Future, which can be used to obtain the results after the task is completed.

Notes

Thread pool size:
• The size of the thread pool should be optimized based on the task type and available resources.
Task dependencies:
• Ensure that there are no dependencies between tasks, otherwise deadlock may result.
Resource leaks:
• Make sure to close all Future objects to prevent resource leaks.
Error handling:
• submit() method will throw exceptions, make sure to catch these exceptions and handle them appropriately.

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