线程局部变量InheritableThreadLocal的使用

本文举例内容来自deepseek&copilot 

1.InheritableThreadLocal 是 Java 中 ThreadLocal 的一个子类，它允许子线程继承父线程的线程局部变量值

InheritableThreadLocal 常用于以下场景：

1. 传递上下文信息（如用户会话、跟踪ID等）到子线程

2. 分布式跟踪系统中的上下文传递

3. 需要在线程间传递特定信息的框架中

public class InheritableThreadLocalDemo {
    //Create an inheritable thread local variable
    private static final ThreadLocal<String> inheritableThreadLocal = new InheritableThreadLocal<>();
    public static void main(String[] args) {
        // Set a value in the main thread
        inheritableThreadLocal.set("BabaMama");
        System.out.println("Value in main thread: " + inheritableThreadLocal.get());

        // Create a child thread
        Thread childThread = new Thread(() -> {
            // Child threads can extend the values set by the parent thread
            System.out.println("Value in child thread: " + inheritableThreadLocal.get());
            //Modifying values in child threads will not affect the parent thread
            inheritableThreadLocal.set("Baby");
            System.out.println("Value in child thread: " + inheritableThreadLocal.get());
        });

        // Start the child thread
        childThread.start();

        try {
            System.out.println("----------start-----------");
            // Wait for the child thread to finish
            childThread.join();
            System.out.println("----------end-------------");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //The value of the main thread is not affected by the child threads
        System.out.println("The final Value in main thread after child thread: " + inheritableThreadLocal.get());
        // Clear the value in the main thread
        inheritableThreadLocal.remove();
    }
}

> Task :InheritableThreadLocalDemo.main()
Value in main thread: BabaMama
----------start-----------
Value in child thread: BabaMama
Value in child thread: Baby
----------end-------------
The final Value in main thread after child thread: BabaMama

2.线程池中的使用

public class ThreadPoolInheritableDemo {

    // Create an inheritable thread local variable
    private static final InheritableThreadLocal<String> inheritableThreadLocal = new InheritableThreadLocal<>();

    public static void main(String[] args) {
        // Set a value in the main thread
        inheritableThreadLocal.set("BabaMama");
        System.out.println("Value in main thread: " + inheritableThreadLocal.get());

        // Create a thread pool
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        // task1 - Initialize the inheritable thread local variable in the main thread
        Runnable task1 = () -> {
            inheritableThreadLocal.set("task1-Initialize");
            System.out.println("task1: " + inheritableThreadLocal.get());
        };
        // task2 - try to get value
        Runnable task2 = () -> {
            System.out.println("task2: " + inheritableThreadLocal.get());
        };
        // Submit task to the thread pool
        executorService.submit(task1);
        executorService.submit(task2);

        // Shutdown the executor service,Waiting for task completion
        executorService.shutdown();

        try {
            System.out.println("----------start-----------");
            // Wait for all tasks to finish
            if (!executorService.awaitTermination(1, TimeUnit.MINUTES)) {
                executorService.shutdownNow();
            }
            System.out.println("----------end-------------");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        // The value of the main thread is not affected by the child threads
        System.out.println("The final Value in main thread after child thread: " + inheritableThreadLocal.get());
        // Clear the value in the main thread
        inheritableThreadLocal.remove();
    }
}

第一次运行可能的结果：

> Task :ThreadPoolInheritableDemo.main()
Value in main thread: BabaMama
----------start-----------
task1: task1-Initialize
task2: BabaMama
----------end-------------
The final Value in main thread after child thread: BabaMama

再次运行，可能的结果如下：

> Task :ThreadPoolInheritableDemo.main()
Value in main thread: BabaMama
----------start-----------
task2: BabaMama
task1: task1-Initialize
----------end-------------
The final Value in main thread after child thread: BabaMama

注意事项

1. 在线程池中使用时要小心，因为线程是复用的，可能导致数据混乱

2. 子线程修改值不会影响父线程的值

3. 可能会引起内存泄漏，使用后应及时清理（调用 remove() 方法）