ThreadLoacl,InheritableThreadLocal,原理,以及配合线程池使用的一些坑
之前为了能让InheritableThreadLocal 正确传递,不得不每次
ExecutorService executor = Executors.newFixedThreadPool(>=[任务线程数]);
或者直接new Thread.
这样不仅引起性能损耗,并且如果并发上来了,会造成不必要的上下文切换.还必须用信号量做并发控制.
偶然发现 阿里开源 TransmittableThreadLocal 可以解决此问题.
以下来实验一下
/** * User: laizhenwei * Date: 2018-04-12 Time: 10:07 * Description: */ public class Ttl { static ExecutorService executorService = Executors.newFixedThreadPool(1); public static void main(String[] args) { //子线程每次new 所以会复制线程的InheritableThreadLocal,结果正确 // withoutThreadPool(10); //因线程池复用线程,不会每次new 所以不会更新父线程InheritableThreadLocal 的值,导致结果错误 withThreadPool(10); } public static void withoutThreadPool(int c){ for(int i=0;i<c;i++){ Integer var1 = (int)(Math.random()*100); Integer var2 = (int)(Math.random()*100); MyContextHolder.set(var1); threadRun(var1,var2); } } public static void withThreadPool(int c){ for(int i=0;i<c;i++){ Integer var1 = (int)(Math.random()*100); Integer var2 = (int)(Math.random()*100); MyContextHolder.set(var1); threadPoolExecute(var1,var2); } } public static void threadRun(Integer var1,Integer var2){ new Thread(()->assert1(var1,var2)).start(); } public static void threadPoolExecute(Integer var1,Integer var2){ executorService.execute(()->assert1(var1,var2)); } public static void assert1(Integer var1,Integer var2){ System.out.println(MyContextHolder.get()*var2==var1*var2); } public static class MyContextHolder{ private static ThreadLocal<Integer> stringThreadLocal = new InheritableThreadLocal<>(); public static void set(Integer data) { stringThreadLocal.set(data); } public static Integer get() { return stringThreadLocal.get(); } } }
withoutThreadPool(10)输出结果
withThreadPool(10); 输出结果
解决方式
pom引入
<!-- https://mvnrepository.com/artifact/com.alibaba/transmittable-thread-local --> <dependency> <groupId>com.alibaba</groupId> <artifactId>transmittable-thread-local</artifactId> <version>2.2.0</version> </dependency>
修改MyContextHolder
public static class MyContextHolder{ private static ThreadLocal<Integer> stringThreadLocal = new TransmittableThreadLocal<>(); // private static ThreadLocal<Integer> stringThreadLocal = new InheritableThreadLocal<>(); public static void set(Integer data) { stringThreadLocal.set(data); } public static Integer get() { return stringThreadLocal.get(); } }
修改threadPoolExecute
public static void threadPoolExecute(Integer var1,Integer var2){
//使用TransmittableThreadLocal 解决
executorService.execute(TtlRunnable.get(()->assert1(var1,var2)) );
// executorService.execute(()->assert1(var1,var2));
}
运行 withThreadPool(10); 结果