Java : InheritableThreadLocal with Examples

January 25, 2024

日本語

InheritableThreadLocal (Java SE 21 & JDK 21) with Examples.
You will find code examples on most InheritableThreadLocal methods.

Summary

try (final var parent1 = Executors.newSingleThreadExecutor();
     final var parent2 = Executors.newSingleThreadExecutor()) {

    final var local = new InheritableThreadLocal<String>();

    parent1.submit(() -> {
        try {
            System.out.println("parent 1 : set = abc");
            local.set("abc");

            TimeUnit.SECONDS.sleep(1);
            System.out.println("parent 1 : get = " + local.get());

            try (final var child = Executors.newSingleThreadExecutor()) {
                child.submit(() -> {
                    System.out.println("child  1 : get = " + local.get());
                });
            }

        } catch (InterruptedException e) {
            System.out.println("InterruptedException!");
        }
    });

    TimeUnit.MILLISECONDS.sleep(100);

    parent2.submit(() -> {
        try {
            System.out.println("parent 2 : set = XYZ");
            local.set("XYZ");

            TimeUnit.SECONDS.sleep(1);
            System.out.println("parent 2 : get = " + local.get());

            try (final var child = Executors.newSingleThreadExecutor()) {
                child.submit(() -> {
                    System.out.println("child  2 : get = " + local.get());
                });
            }

        } catch (InterruptedException e) {
            System.out.println("InterruptedException!");
        }
    });
}

// Result
// ↓
//parent 1 : set = abc
//parent 2 : set = XYZ
//parent 1 : get = abc
//child  1 : get = abc
//parent 2 : get = XYZ
//child  2 : get = XYZ

Constructors

final var local = new InheritableThreadLocal<String>();
System.out.println(local.get()); // null

local.set("abc");
System.out.println(local.get()); // abc

final var local = new InheritableThreadLocal<Integer>();
System.out.println(local.get()); // null

local.set(123);
System.out.println(local.get()); // 123

Methods

try (final var parent = Executors.newSingleThreadExecutor()) {

    final var local = new InheritableThreadLocal<String>() {
        @Override
        protected String childValue(String parentValue) {
            System.out.println("-- childValue --");
            System.out.println("  parentValue = " + parentValue);

            return parentValue.toUpperCase();
        }
    };

    parent.submit(() -> {
        local.set("abc");
        System.out.println("parent : get = " + local.get());

        try (final var child = Executors.newSingleThreadExecutor()) {
            child.submit(() -> {
                System.out.println("child : get = " + local.get());
            });
        }
    });
}

// Result
// ↓
//parent : get = abc
//-- childValue --
//  parentValue = abc
//child : get = ABC

Methods declared in ThreadLocal

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