ThreadLoacl,InheritableThreadLocal,原理,以及配合線程池使用的一些坑

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TransmittableThreadLocal?原理

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之前為了能讓InheritableThreadLocal?正確傳遞,不得不每次

ExecutorService executor = Executors.newFixedThreadPool(>=[任務(wù)線程數(shù)]);
或者直接new Thread.

這樣不僅引起性能損耗,并且如果并發(fā)上來了,會(huì)造成不必要的上下文切換.還必須用信號(hào)量做并發(fā)控制.
偶然發(fā)現(xiàn) 阿里開源 TransmittableThreadLocal?可以解決此問題.
以下來實(shí)驗(yàn)一下

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/*** 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) {//子線程每次new 所以會(huì)復(fù)制線程的InheritableThreadLocal,結(jié)果正確 // withoutThreadPool(10);//因線程池復(fù)用線程,不會(huì)每次new 所以不會(huì)更新父線程InheritableThreadLocal 的值,導(dǎo)致結(jié)果錯(cuò)誤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)輸出結(jié)果

withThreadPool(10); 輸出結(jié)果

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解決方式

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 解決executorService.execute(TtlRunnable.get(()->assert1(var1,var2)) ); // executorService.execute(()->assert1(var1,var2));}

運(yùn)行?withThreadPool(10);?結(jié)果

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總結(jié)

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