blocks|key|1487482|text|是的，你可以用Concurrent+ML中的消息传递很好地做到这一点。不要被系统的时代所拖累；John+Reppy的book和论文是这个主题的优秀指南。漂亮的东西！|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1487483|entityMap|0|LINK|mutability|MUTABLE|url|http://cml.cs.uchicago.edu/|1|https://rads.stackoverflow.com/amzn/click/com/0521480892^0|7|D|0|1M|4|1|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]|$A|R|B|S|1|T]]|C|$]]|$1|D|3|-4|5|6|7|U|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]|L|$5|G|H|I|C|$J|M]]]]

Yes, you can do it quite nicely with message passing in <a href="http://cml.cs.uchicago.edu/" rel="nofollow noreferrer">Concurrent ML</a>. Don't be put off by the age of the system; John Reppy's <a href="https://rads.stackoverflow.com/amzn/click/com/0521480892" rel="nofollow noreferrer" rel="nofollow noreferrer">book</a> and papers are excellent guides to the topic. Beautiful stuff!

blocks|key|186075|text|拥有多个线程必然需要不纯的(非功能的)操作。纯函数式编程将您的应用程序视为函数的求值。同时评估两个事物并在它们之间传递数据的概念在此框架内没有意义。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|186076|尽管可以并行计算函数的多个部分，就像在Haskell的par运算符中一样，但这与生产者-消费者问题不同，因此我认为您无法用函数方式解决它。|offset|length|186077|entityMap|0|LINK|mutability|MUTABLE|url|http://www.haskell.org/ghc/docs/latest/html/libraries/parallel/Control-Parallel.html#v%253Apar^0|0|R|3|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Having multiple threads necessarily requires impure (non-functional) actions. Pure functional programming considers your application to be the evaluation of a function. The concept of concurrently evaluating two things and passing data between them is not meaningful within this framework.

Although one can evaluate multiple parts of a function in parallel, as in Haskell's <a href="http://www.haskell.org/ghc/docs/latest/html/libraries/parallel/Control-Parallel.html#v%3Apar" rel="nofollow noreferrer">``par<code></code></a> operator, this is not the same as the producer-consumer problem, and as such I don't think you'll be able to solve it in a functional way.

blocks|key|1487566|text|是。查看函数式反应编程(FRP)，它与并发ML+(Norman的建议)有关，但它是纯粹的函数式编程。FRP的语义是高度“并发”的，同时具有简单、精确、确定的功能语义模型(时间函数)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1487567|编辑:我在这里引用了“并发”，因为我不是指通常的操作(面向实现)的并发概念，它是强制性的和非确定性的，因此阻碍了实际和可靠的正确推理。|1487568|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Yes. Check out functional reactive programming (FRP), which is related to Concurrent ML (Norman's suggestion) but is purely functional. The semantics of FRP is highly "concurrent" while having a simple, precise, deterministic, functional semantic model (functions of time).

Edit: I quoted "concurrent" here, because I do not mean the usual operational (implementation-oriented) notion of concurrency, which is imperative and non-deterministic, thus impeding practical &amp; dependably correct reasoning.

blocks|key|1487405|text|我在SML中看到的所有生产者-消费者的实现都被迫依赖于ref(为了维护一个“休眠”项的队列)，所以我倾向于说“不”。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1487406|entityMap^0|R|3|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

All of the implementations I've seen of producer-consumer in SML were forced to rely on <code>ref</code>s (in order to maintain a queue of 'sleeping' items), so I'd be inclined to say "no".

blocks|key|186095|text|有很多方法可以解决这个问题；每种方法都有不同的缺点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|186096|例如，"put“每次都会产生一个新的线程。这样一来，你就完全不需要缓冲区了。如果有很多请求进来，你就会产生很多线程，直到你的CPU在线程之间的切换比实际执行它们更忙。但这只是将问题从您的代码转移到操作系统中:在某个点上，您总是必须同步对内存中变量的访问。操作系统必须维护一个线程列表，并且必须同步对该列表的访问。|186097|或者你想限制线程的数量(然后"put“必须能够读取变量，而线程可能在同一时间终止并递减它，再次同步访问->+)。否则，您可能会因为线程太多而耗尽资源。|186098|您可以在调用"put“时发布一条消息，消费者可以收听该消息。但这只是实现线程“等待”的一种复杂方式。而且您需要一种方法来确保只有一个消费者收到消息。同样，您还需要一些同步的数据结构。|186099|所以最后，问题并不在于赋值，而在于对单个变量的并发访问，无论您如何尝试，对于任何produce+consumer实现，您都必须能够做到这一点(否则整个系统将是单线程的)。|186100|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|O|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

There are many way to solve this; each has different drawbacks.

For example, the "put" could spawn a new thread each time. That way, you wouldn't need a buffer at all. If lots of requests come in, you spawn lots of threads until your CPU is more busy with switching between threads than actually executing them. But this just moves the problem from your code into the OS: At a certain point, you always have to synchronize access to a variable in memory. The OS must maintain a list of threads and access to this list must be synchronized.

Either you want to limit the number of threads (then a "put" must be able to read the variable while threads might terminate at the same time and decrement it -> again synchronized access). Or you risk running out of resources because you have too many threads.

You could post a message when "put" is called and the consumers could listen to the message. But that's only a complex way to implement "wait" for threads. And you need a way to make sure that only a single consumer gets the message. Again, you'll need some synchronized data structure.

So in the end, it's not really the assignment, which is the problem, but concurrent access to a single variable and no matter how you try, for any implementation of produce-consumer, you must be able to do this (or the whole will be single threaded).

I am interested in finding if producer-consumer problem when there are multiple produce and multiple consumer be solved without using assignment i.e., using functional style of programming? How?

<a href="http://en.wikipedia.org/wiki/Producer-consumer_problem" rel="nofollow noreferrer">Producer-consumer problem</a>

Thanks

producer-consumer using assignment

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我感兴趣的是，当有多个生产者和多个消费者时，生产者-消费者问题是否可以在不使用赋值的情况下解决，即使用函数式编程风格？多么?谢谢

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