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阿里巴巴TransmittableThreadLocal使用介绍

2025-02-15 | 佚名 | 点击：次

ThreadLocal在上下文的数据传输上非常的方便和简洁。

工业实践中，比较常用的有三个，ThreadLocal、InheritableThreadLocal、TransmittableThreadLocal，那么他们三个之间有什么区别呢？

常见的三种ThreadLocal比较

  ThreadLocal InheritableThreadLocal TransmittableThreadLocal
来源 jdk jdk 阿里开源
单线程数据传输 支持 支持 支持
new线程数据传输 不支持 支持 支持
线程池数据传输 不支持 部分支持【简单场景】 支持

针对线程池的数据传输，InheritableThreadLocal仅仅能在一些简单场景下做到，下面就用一个案例来说明

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package com.tml.mouseDemo.core.threadLocalDemo;

 

import java.util.concurrent.ThreadFactory;

import java.util.concurrent.atomic.AtomicInteger;

 

public class SimpleThreadFactory implements ThreadFactory {

 

    private static AtomicInteger atomicInteger = new AtomicInteger(1);

    @Override

    public Thread newThread(Runnable r) {

 

        Thread t = new Thread(r);

        t.setName("tml-"+atomicInteger.getAndIncrement());

        return t;

    }

}

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package com.tml.mouseDemo.core.threadLocalDemo;

 

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class ThreadLocalDemo1 {

 

    private static ThreadLocal<String> threadLocal = new InheritableThreadLocal<>();

 

    private static ExecutorService service = Executors.newFixedThreadPool(2, new SimpleThreadFactory());

 

 

    public static void main(String[] args) throws InterruptedException {

 

 

        threadLocal.set("hello main");

        for (int i = 0; i < 2; i++) {

            service.execute(() -> {

                String s = threadLocal.get();

                ThreadUtils.printLog("get data " + s);

 

            });

        }

 

        //修改threadLocal中的值

        threadLocal.set("hello world");

        Thread.sleep(2000);

        for (int i = 0; i < 2; i++) {

 

            service.execute(() -> {

                String s = threadLocal.get();

                ThreadUtils.printLog("get data " + s);

 

            });

        }

 

 

        ThreadUtils.printLog("get data " + threadLocal.get());

 

        service.shutdown();

 

    }

}

2025-01-10 19:41:50 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:41:50 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:41:52 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:41:52 | INFO | main | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 19:41:52 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main

从运行结果来看，前面的两次循环提交的任务，在子线程中确实是能正常的获取主线程设置的变量，即hello main，但是紧接着，我修改了主线程上绑定的变量为hello world，然后继续循环两次提交两个任务，这个时候子线程中获取的线程变量依然是hello main，这明显是与是期望不一致的。

从这个层面来讲，InheritableThreadLocal确实在线程池的层面支持不够友好，可以说仅支持部分简单场景。

根本原因就死线程池的池化机制，从上面的运行日志上也可以看出，提交了4个任务执行的线程依然是两个。线程池中的线程是复用的，InheritableThreadLocal是在创建子线程的时候，会将主线程上绑定的数据拷贝过来，如果我不创建新的线程，但是主线程上绑定的数据改变了呢？那我依然还是读取到之前拷贝的数据。

这个就是InheritableThreadLocal的短板。针对这个问题，阿里开源的TransmittableThreadLocal就能顺利丝滑的解决这个问题。

TransmittableThreadLocal实践

maven依赖

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<dependency>

     <groupId>com.alibaba</groupId>

    <artifactId>transmittable-thread-local</artifactId>

     <version>2.12.4</version>

</dependency>

装饰Runnable任务

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package com.tml.mouseDemo.core.threadLocalDemo;

 

import com.alibaba.ttl.TransmittableThreadLocal;

import com.alibaba.ttl.TtlRunnable;

 

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class ThreadLocalDemo1 {

 

    private static ThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();

 

    private static ExecutorService service = Executors.newFixedThreadPool(2, new SimpleThreadFactory());

 

 

    public static void main(String[] args) throws InterruptedException {

 

 

        threadLocal.set("hello main");

        for (int i = 0; i < 2; i++) {

            service.execute(TtlRunnable.get(() -> {

                String s = threadLocal.get();

                ThreadUtils.printLog("get data " + s);

 

            }));

        }

 

        //修改threadLocal中的值

        threadLocal.set("hello world");

        Thread.sleep(2000);

        for (int i = 0; i < 2; i++) {

 

            service.execute(TtlRunnable.get(() -> {

                String s = threadLocal.get();

                ThreadUtils.printLog("get data " + s);

 

            }));

        }

 

 

        ThreadUtils.printLog("get data " + threadLocal.get());

 

        service.shutdown();

 

    }

}

2025-01-10 19:57:03 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:57:03 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:57:05 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 19:57:05 | INFO | main | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 19:57:05 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world

与第一个案例的差异点在于，使用了

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public static TtlRunnable get(@Nullable Runnable runnable) {

    return get(runnable, false, false);

}

来增强了了Runnable任务，执行的结果也是符合预期。

装饰线程池

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package com.tml.mouseDemo.core.threadLocalDemo;

 

import com.alibaba.ttl.TransmittableThreadLocal;

import com.alibaba.ttl.TtlRunnable;

import com.alibaba.ttl.threadpool.TtlExecutors;

 

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class ThreadLocalDemo1 {

 

    private static ThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();

 

    private static ExecutorService service = Executors.newFixedThreadPool(2, new SimpleThreadFactory());

 

    private static ExecutorService ttlExecutorService = TtlExecutors.getTtlExecutorService(service);

 

 

 

    public static void main(String[] args) throws InterruptedException {

 

 

 

        threadLocal.set("hello main");

        for (int i = 0; i < 2; i++) {

            ttlExecutorService.execute(() -> {

                String s = threadLocal.get();

                ThreadUtils.printLog("get data " + s);

 

            });

        }

 

        //修改threadLocal中的值

        threadLocal.set("hello world");

        Thread.sleep(2000);

        for (int i = 0; i < 2; i++) {

 

            ttlExecutorService.execute(() -> {

                String s = threadLocal.get();

                ThreadUtils.printLog("get data " + s);

 

            });

        }

 

 

        ThreadUtils.printLog("get data " + threadLocal.get());

 

        service.shutdown();

 

    }

}

2025-01-10 20:05:05 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 20:05:05 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 20:05:07 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 20:05:07 | INFO | main | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 20:05:07 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world

与上一个案例的差异点在于，这里没有包装Runnable任务，而是包装了线程池，使用了

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public static ExecutorService getTtlExecutorService(@Nullable ExecutorService executorService) {

    if (TtlAgent.isTtlAgentLoaded() || executorService == null || executorService instanceof TtlEnhanced) {

        return executorService;

    }

    return new ExecutorServiceTtlWrapper(executorService, true);

}

包装了ExecutorService，执行结果也是符合预期

使用java Agent无侵入增强线程池

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package com.tml.mouseDemo.core.threadLocalDemo;

 

import com.alibaba.ttl.TransmittableThreadLocal;

 

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class ThreadLocalDemo1 {

 

    private static ThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();

 

    private static ExecutorService service = Executors.newFixedThreadPool(2, new SimpleThreadFactory());

 

    public static void main(String[] args) throws InterruptedException {

 

 

 

        threadLocal.set("hello main");

        for (int i = 0; i < 2; i++) {

            service.execute(() -> {

                String s = threadLocal.get();

                ThreadUtils.printLog("get data " + s);

 

            });

        }

 

        //修改threadLocal中的值

        threadLocal.set("hello world");

        Thread.sleep(2000);

        for (int i = 0; i < 2; i++) {

 

            service.execute(() -> {

                String s = threadLocal.get();

                ThreadUtils.printLog("get data " + s);

 

            });

        }

 

 

        ThreadUtils.printLog("get data " + threadLocal.get());

 

        service.shutdown();

 

    }

}

项目运行的时候，需要添加额外的jvm启动参数，如下

2025-01-10 20:11:59 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 20:11:59 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 20:12:01 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 20:12:01 | INFO | main | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 20:12:01 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world

总结

阿里巴巴的TransmittableThreadLocal是继承自InheritableThreadLocal，对他的功能进行了增强，增强的点也主要是在线程池的支持上。

通过上面的三个案例，可以看到TransmittableThreadLocal是非常灵活的，大家可以根据自己的需要，选择对应的方式来实现。

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