并发神器CSP的前世今生

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"本文转自“雨夜随笔”公众号，欢迎关注。"}]},{"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":"程序架构的研究在上世纪七八十年代还处于原始阶段，当时的大部分研究都在研究如何编写顺序代码，而现在所熟知的goto语句那时也正在被讨论，还没有正式引入。而面向对象的范式正在悄悄的变成编程的基石。"}]},{"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":"一切都显得风平浪静，好像一切都在随着预想的慢慢发展。这时"},{"type":"text","marks":[{"type":"strong"}],"text":"Charles"},{"type":"text","text":" "},{"type":"text","marks":[{"type":"strong"}],"text":"Antony"},{"type":"text","text":" "},{"type":"text","marks":[{"type":"strong"}],"text":"Richard"},{"type":"text","text":" "},{"type":"text","marks":[{"type":"strong"}],"text":"Hoare (简称Tony Hoare)"},{"type":"text","text":"发现了一个问题，那就是并发没有得到太多的关注，于是他开始着手解决这个问题。"}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"Tony Hoare"}]},{"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/c7/c74ffbaf965c73baabd3919dcbf5530c.jpeg","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":"说起"},{"type":"text","marks":[{"type":"strong"}],"text":"Tony Hoare"},{"type":"text","text":"，初听比较陌生。但是他的另一项研究很多程序员不会陌生，那就是排序算法中的"},{"type":"text","marks":[{"type":"strong"}],"text":"快速排序算法（Quick Sort）"},{"type":"text","text":"。而这个闻名于世的算法是他26岁时发明的，当然除了这些，Tony Hoare在程序设计语言的定义、设计、数据结构、算法和操作系统等许多方面都有很多影响深远的成果。并因为“对程序设计语言的定义和设计方面的基础性贡献”在1980年获得图灵奖。"}]},{"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":"Hoare在发明快速排序后的第二年，接到了新的任务，为公司的新机器设计一个新的高级语言，而当时他正好搞到一份Algol 60报告的复印件，并参加了Dijkstra（学算法的时候大部分人都听过Dijkstra算法，没错，就是这个人发明的）等人剧本的Algol 60培训班。当时Hoare学着学着就想，不如直接把Algol 60在公司的新机器上进行实现。于是Hoare把这个想法提交给公司，在公司同意后，开始设计和实现Algol 60的一个自己版本。Hoare在一开始就制定了明确的目标，即系统要安全可靠，生成的目标码要简洁，工作区数据要紧凑，过程和函数的人口和出口要清晰、严密等，还明确了整个编译过程采用一次扫描等原则。"}]},{"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":"而这次实现不仅十分顺利，并且大受欢迎，在世界各国开发的Algol 60版本中效率、可靠性和方便性都非常出色。因此得到了国际学术界的重视。国际信息处理联盟于是任命霍尔为2.1工作组(Working Group 2.1)的负责人，这个工作组的任务是维护和发展Algol。霍尔果然不负众望，主持设计了Algol X以继承与发展Algol 60。正是在Algol X的设计中，霍尔发明了"},{"type":"text","marks":[{"type":"strong"}],"text":"CASE语句"},{"type":"text","text":"。"}]},{"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":"Hoare还有很多重要的研究和成果。而我们今天要说的CSP理论就是其中非常重要的一点。"}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"CSP"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2c/2c146f4433df559951445db9e5b69c66.png","alt":"image.png","title":"image.png","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":"Hoare在发现并发操作没有引起过多的关注后，开始着手进行解决。终于在1978年，Hoare在ACM中发表了经典的“"},{"type":"text","marks":[{"type":"strong"}],"text":"Communicating Sequential Processes"},{"type":"text","text":"”论文。在这篇论文中，Hoare认为输入和输出是两个被忽略的编程原语，尤其在并发代码中。于是Hoare在CSP论文中展示了如何应用通信来建模输入和输出，并提供了如何用CSP来解决一些并发问题，比如寻找10000以内的素数。通过这种方式最终达到“在进程间正确的通信”。当然这个思想在当时是非常超前的，事实上，1978年的论文中，CSP只是一个用来展示通信顺序进程的能力的一个简单的编程语言。连Hoare本身都觉得这个想法过于超前而有些不切实际，他直接在论文中悲观的写道："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"Thus the concepts and notations introduced in this paper (although described in the next section in the form of a programming language fragment) should not be regarded as suitable for use as a programming language, either for abstract or for concrete programming. They are at best only a partial solution to the problems tackled."}]},{"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":"本文介绍的概念和符号应该不被认为适合作为一种编程语言，无论是抽象的还是具体的编程。他们最多只是一种解决问题的方式。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Hoare担心自己所展示的技术对于未来的并发编程的研究并没有任何作用，这种技术或许没有语言能够按照他的想法来实现。但是接下来的6年里，关于CSP的想法被提炼成对并发系统进行数学建模的方法--进程微积分。并提供了代数规则来对系统进行变化来分析它们的并发和效率。而这正式将CSP的想法投入到并发编程的实践中。"}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"Go语言"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/fd/fdbfde52926c4baaaf595157091372f8.jpeg","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":"在CSP提出后，有些语言尝试将Hoare提出的输入和输出作为原语纳入到自己的语言体系中，比如OCCAM并发处理语言。和传统的加锁方式不同，CSP理论中不允许进程对其他进程的变量赋值，进程之间只能通过通信原语来实现数据交换和协作。但是这些语言都没能真正地为这些原语提供支持。大多数流行语言都支持共享和内存访问同步到CSP的消息传递样式。而采用CSP理论的语言也有，但是基本都没有得到广泛的采用。"}]},{"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":"直到Go语言出现，正式将CSP的原则纳入到核心原则，并提供了通信的原语支持channel。正因为如此，并发被认为是Go语言的优势之一。并让Go语言在分布式系统、云原生系统和系统中间件中迅速占领了市场。而其他语言基于共享内存的并发模型，在大型和复杂系统中变得很难正确使用。"}]},{"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":"当然Go还有其局限性，因为CSP的理解成本问题，Go同时也支持传统的加锁方式，也支持共享内存的方式。不过Go已经向其他语言证明CSP的可行性和优越处。并且提出了经典的CSP核心概念："}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"Do not communicate by sharing memory; instead, share memory by communicating."}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"}],"text":"“不要以共享内存的方式来通信，相反，要通过通信来共享内存。”"}]}]},{"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":"而由于Go语言的推广和效果，使得CSP的概念变得流行起来，目前很多语言在尝试将CSP纳入到语言体系中并提供对Hoare提出原语的支持。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c9/c939a3a0dd5faddfd4735ad855b3f940.jpeg","alt":null,"title":"欢迎关注","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"https://mp.weixin.qq.com/s?__biz=Mzg4MTIwMTkxNQ==&mid=2247483984&idx=1&sn=fcb9059af0683f376c0e5217eb34948d&chksm=cf68c5c4f81f4cd20ea522e5a74aac33bc41bc80e637297d247fbe03d340b5efb154b270ed79&scene=126&sessionid=1598237124&key=8723f2e63c89806b326e12d15b3035df06d4e5417a59f8e122596b47e313a1114c3fb61710f299a02486636efbb1fdc79595ed216330c39c417366566330e3b6b828c727b23e4f04c45b2cc846c2dba3ceceaddbbd5f307aaa079e5a8aa9a03b312fe8127775596fa1a00abe78f5115f19dd9794190089d10fb2107bfe661520&ascene=1&uin=NTkyMjg4NQ%3D%3D&devicetype=Windows+10+x64&version=62090529&lang=zh_CN&exportkey=AQi0GXuW4X8tGiEPZLGcpsU%3D&pass_ticket=yNZPWKpTbcA3%2FE%2B88J6cWPMPQdU940sRHRL4IUkzBPg%3D","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"参考链接"}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"计算机科学名人堂：Charles Antony Richard Hoare："},{"type":"link","attrs":{"href":"http://wap.sciencenet.cn/blog-1225851-839515.html","title":null},"content":[{"type":"text","text":"http://wap.sciencenet.cn/blog-1225851-839515.html"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Go语言CSP：通信顺序进程简述："},{"type":"link","attrs":{"href":"https://tsov.net/uupee/17044/","title":null},"content":[{"type":"text","text":"https://tsov.net/uupee/17044/"}]}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"CSP 1978论文："},{"type":"link","attrs":{"href":"https://spinroot.com/courses/summer/Papers/hoare_1978.pdf?__cf_chl_captcha_tk__=637000f92bddaa467d97d4404b8c86d40e787bda-1590473325-0-AfwfleSjOLTLNc9NlYQOaERH30eugvvD_pZCpJQp1BuLY7h8FMzdU-1g6gibzt0oPufEBr6ny7EMfaDuavQM9RoUnT5c1kqmUsycipyMJOPCp7-be5mLk7qFSZZm0dWcHb2HuOTkKQpAdCMgqSC4mBSfZ8UvZWjJ3v6kFE6MfP3BnQBtubXk88o3Twg3k8pd8W7xECjsYgSeyLB3xxq9y4-cpagfl0piK4i9QA00A2-Vm5usNU_WVevL5u-tepVkPdZpm8WQITYmKVeU_dTsBWv7Gpal-a1qATffyGGhAweQWYoDSpoO6uj8get5D_7cGe6jkzJEXaq04kHOABe9Us9BKs6qNOV7lE-Xdk7q1EKV","title":null},"content":[{"type":"text","text":"https://spinroot.com/courses/summer/Papers/hoare_1978.pdf?__cf_chl_captcha_tk__=637000f92bddaa467d97d4404b8c86d40e787bda-1590473325-0-AfwfleSjOLTLNc9NlYQOaERH30eugvvD_pZCpJQp1BuLY7h8FMzdU-1g6gibzt0oPufEBr6ny7EMfaDuavQM9RoUnT5c1kqmUsycipyMJOPCp7-be5mLk7qFSZZm0dWcHb2HuOTkKQpAdCMgqSC4mBSfZ8UvZWjJ3v6kFE6MfP3BnQBtubXk88o3Twg3k8pd8W7xECjsYgSeyLB3xxq9y4-cpagfl0piK4i9QA00A2-Vm5usNU_WVevL5u-tepVkPdZpm8WQITYmKVeU_dTsBWv7Gpal-a1qATffyGGhAweQWYoDSpoO6uj8get5D_7cGe6jkzJEXaq04kHOABe9Us9BKs6qNOV7lE-Xdk7q1EKV"}]}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}