一文带你彻底了解Java异步编程

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"随着","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"RxJava","attrs":{}}],"attrs":{}},{"type":"text","text":"、","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Reactor","attrs":{}}],"attrs":{}},{"type":"text","text":"等异步框架的流行,异步编程受到了越来越多的关注,尤其是在IO密集型的业务场景中,相比传统的同步开发模式,异步编程的优势越来越明显。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那到底什么是异步编程?异步化真正的好处又是什么?如何选择适合自己团队的异步技术?在实施异步框架落地的过程中有哪些需要注意的地方?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文从以下几个方面结合真实项目异步改造经验对异步编程进行分析,希望能给大家一些客观认识:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"numberedlist","attrs":{"start":null,"normalizeStart":1},"content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":1,"align":null,"origin":null},"content":[{"type":"text","text":"使用RxJava异步改造后的效果","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":2,"align":null,"origin":null},"content":[{"type":"text","text":"什么是异步编程?异步实现原理","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":3,"align":null,"origin":null},"content":[{"type":"text","text":"异步技术选型参考","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":4,"align":null,"origin":null},"content":[{"type":"text","text":"异步化真正的好处是什么?","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":5,"align":null,"origin":null},"content":[{"type":"text","text":"异步化落地的难点及解决方案","attrs":{}}]}],"attrs":{}},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":6,"align":null,"origin":null},"content":[{"type":"text","text":"扩展:异步其他解决方案-协程","attrs":{}}]}],"attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"使用RxJava异步改造后的效果","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下图是我们后端java项目使用RxJava改造成异步前后的RT(响应时长)效果对比:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bb/bbf333e4de4a636b19fad308ff3fc96f.png","alt":"image","title":"image","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/81/81b7bed774d0989c8c7efde73221d10f.png","alt":"image","title":"image","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"统计数据基于App端的gateway,以75线为准,还有80、85、90、99线,从图中可以看出改成异步后接口整体的平均响应时长降低了","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"40%","attrs":{}},{"type":"text","text":"左右。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"(响应时间是以发送请求到收到后端接口响应数据的时长,上图改造的这个后端java接口内部流程比较复杂,因为公司都是微服务架构,该接口内部又调用了6个其他服务的接口,最后把这些接口的数据汇总在一起返回给前端)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这张图是同步接口和改造成异步接口前后的CPU负载情况对比","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"改造前cpu load : 35.46","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/19/1906172d5c201de458f88a35c35eae67.png","alt":"image","title":"image","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"改造后cpu load : 14.25","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2b/2b6a3c4b3d9b8bfa4221f3f8105900a2.png","alt":"image","title":"image","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"改成异步后CPU的负载情况也有明显下降,但CPU使用率并无影响(一般情况下异步化后cpu的利用率会有所提高,但要看具体的业务场景)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"CPU LoadAverage是指:一段时间内处于可运行状态和不可中断状态的进程平均数量。(可运行分为正在运行进程和正在等待CPU的进程;","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"不可中断则是它正在做某些工作不能被中断比如等待磁盘IO、网络IO等","attrs":{}},{"type":"text","text":")","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"而我们的服务业务场景大部分都是IO密集型业务,功能实现很多需要依赖底层接口,会进行频繁的IO操作。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下图是2019年在全球架构师峰会上","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"阿里","attrs":{}},{"type":"text","text":"分享的异步化改造后的RT和QPS效果:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f2/f2db125c8dcfe37d8ca812f8fcecbe41.png","alt":"image","title":"image","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"(图片来源:淘宝应用架构升级——反应式架构的探索与实践)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"什么是异步编程?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"响应式编程 + NIO","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1. 异步和同步的区别:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我们先从","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"I/O","attrs":{}},{"type":"text","text":"的角度看下同步模式下接口A调用接口B的交互流程:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下图是传统的同步模式下io线程的交互流程,可以看出io是阻塞的,即bio的运行模式","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/65/654c6edb88dca21d27e76a89eb6ca895.png","alt":"image","title":"image","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"接口A发起调用接口B后,这段时间什么事情也不能做,主线程阻塞一直等到接口B数据返回,然后才能进行其他操作,可想而知如果接口A调用的接口不止B的话(A->B->C->D->E。。。),那么等待的时间也是递增的,而且","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"这期间CPU也要一直占用着","attrs":{}},{"type":"text","text":",白白浪费资源,也就是上图看到的 cpu load 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-> C -> D -> E -> F -> G)返回聚合数据","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"背景:使用Jemter测试工具压测100个线程并发请求接口,以观察线程的运行情况(可以全屏观看):","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"video","attrs":{"videoHTML":""}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"codeinline","content":[{"type":"text","text":"http-nio-8080-exec*","attrs":{}}],"attrs":{}},{"type":"text","text":"开头的是tomcat线程池中的线程,即前端请求我们后端接口时要通过tomcat服务器接收和转发的线程,因为我们后端api接口内部又调用了其他服务的6个接口(B、C、D、E、F、G),同步模式下需要等待上一个接口返回数据才能继续调用下一个接口,所以可以从视频中看出,大部分的http线程耗时都在8秒以上(绿色线条代表线程是\"运行中\"状态,8秒包括等待接口返回的时间和我们内部逻辑处理的总时间,因为是本地环境测试,受机器和网络影响较大)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"然后我们再看下异步模式的交互流程,即nio方式:","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/8b/8bc91d61e94ae8ab4f3fbf7cca5a0f65.png","alt":"image","title":"image","style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"大致流程就是接口A发起调用接口B的请求后就立即返回,而不用阻塞等待接口B响应,这样的好处是","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"http-nio-8080-exec*","attrs":{}}],"attrs":{}},{"type":"text","text":"线程可以","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"马上得到复用,接着处理下一个前端请求的任务","attrs":{}},{"type":"text","text":",如果接口B处理完返回数据后,会有一个回调线程池处理真正的响应,即这种模式下我们的业务流程是","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"http线程只处理请求,回调线程处理接口响应","attrs":{}},{"type":"text","text":"。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这个视频演示了异步模式下接口A的线程执行情况,同样也是使用Jemter测试工具压测100个线程并发请求接口,以观察线程的运行情况(可以全屏观看):","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"video","attrs":{"videoHTML":""}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"模拟的条件和同步模式一样,同样是100个线程并发请求接口,但这次","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"http-nio-8080-exec*","attrs":{}}],"attrs":{}},{"type":"text","text":"开头的线程只处理请求任务,而不再等待全部的接口返回,所以http的线程运行时间普遍都很短(大部分在1.8秒左右完成),","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"AsfThread-executor-*","attrs":{}}],"attrs":{}},{"type":"text","text":"是我们系统封装的回调线程池,处理底层接口的真正响应数据。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"演示视频中的","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"AsfThread-executor-*","attrs":{}}],"attrs":{}},{"type":"text","text":"的回调线程只创建了30多个,而请求的http线程有100个,也就是说这30多个回调线程处理了接口B的100次响应(其实应该是600次,因为接口B内部又调用了6个其他接口,这6次也都是在异步线程里处理响应的),因为每个接口返回的时间不一样,加上网络传输的时间,所以可以利用这个时间差充分复用线程即cpu资源,视频中回调线程","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"AsfThread-executor-*","attrs":{}}],"attrs":{}},{"type":"text","text":"的绿色运行状态是多段的,表示复用了多次,也就是少量回调线程处理了全部(600次)的响应,这正是","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"IO多路复用","attrs":{}},{"type":"text","text":"的机制。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"nio模式下虽然","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"http-nio-8080-exec*","attrs":{}}],"attrs":{}},{"type":"text","text":"线程和回调线程","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"AsfThread-executor-*","attrs":{}}],"attrs":{}},{"type":"text","text":"的运行时间都很短,但是从http线程开始到asf回调处理完返回给前端结果的时间和bio即同步模式下的时间差异不大(在相同的逻辑流程下),并不是nio模式下服务响应的整体时间就会缩短,而是","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"会提升CPU的利用率","attrs":{}},{"type":"tex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