Threadlocal在线程池场景下如何传值

客官°小女子只卖身不卖艺 2023-01-21 15:27 5阅读 0赞

我们使用InheritableThreadLocal可以保证在子线程中拿到父线程设置的ThreadLocal的值，它在创建子线程时通过复制父线程的ThreadLocal的值来保证ThreadLocal的值的传递。但是在线程池这种线程复用的场景下，不会每次都创建线程。这就导致了ThreadLocal的值传递不起作用。例如如下例子:

static ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(3,
                3,
                0,
                TimeUnit.SECONDS,
                new SynchronousQueue<>(),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.AbortPolicy());
    
        public static void main(String[] args) throws InterruptedException {
            InheritableThreadLocal<Object> threadLocal = new InheritableThreadLocal<>();
            threadLocal.set(5);
            for(int i = 0; i < 3; i++){
                threadPoolExecutor.submit(() ->{
                    log.info("threadlocal的值:{}", threadLocal.get());
                });
            }
            threadLocal.remove();
            Thread.sleep(1000);
            threadLocal.set(3);
            for(int i = 0; i < 3; i++){
                threadPoolExecutor.submit(() ->{
                    log.info("threadlocal的值:{}", threadLocal.get());
                });
            }
            threadLocal.remove();
        }

这个时候可以使用阿里开发出来的TransmittableThreadLocal来让线程池提交任务时进行ThreadLocal的值传递。将代码稍加改造即可。

1.引入ttl的依赖。

<dependency>
                <groupId>com.alibaba</groupId>
                <artifactId>transmittable-thread-local</artifactId>
                <version>2.12.1</version>
            </dependency>

2.稍加改造代码

static ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(3,
                3,
                0,
                TimeUnit.SECONDS,
                new SynchronousQueue<>(),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.AbortPolicy());
    
        public static void main(String[] args) throws InterruptedException {
            ExecutorService ttlExecutorService = TtlExecutors.getTtlExecutorService(threadPoolExecutor);
            InheritableThreadLocal<Object> threadLocal = new TransmittableThreadLocal<>();
            threadLocal.set(5);
            for(int i = 0; i < 3; i++){
                ttlExecutorService.submit(() ->{
                    log.info("threadlocal的值:{}", threadLocal.get());
                });
            }
            threadLocal.remove();
            Thread.sleep(1000);
            threadLocal.set(3);
            for(int i = 0; i < 3; i++){
                ttlExecutorService.submit(() ->{
                    log.info("threadlocal的值:{}", threadLocal.get());
                });
            }
            threadLocal.remove();
        }

这样就可以保证在线程池下也可以实现ThreadLocal的传递。