什么是协程?它们与并发性有什么关系?


当前回答

我发现大多数答案都太专业了,尽管这是一个技术问题。我很难理解协同程序的过程。我有点明白,但我不能同时明白。

我发现这个答案非常有用:

https://dev.to/thibmaek/explain-coroutines-like-im-five-2d9

引用伊丹·阿耶的话:

To build on your story, I'd put it something like this: You start watching the cartoon, but it's the intro. Instead of watching the intro you switch to the game and enter the online lobby - but it needs 3 players and only you and your sister are in it. Instead of waiting for another player to join you switch to your homework, and answer the first question. The second question has a link to a YouTube video you need to watch. You open it - and it starts loading. Instead of waiting for it to load, you switch back to the cartoon. The intro is over, so you can watch. Now there are commercials - but meanwhile a third player has joined so you switch to the game And so on... The idea is that you don't just switch the tasks really fast to make it look like you are doing everything at once. You utilize the time you are waiting for something to happen(IO) to do other things that do require your direct attention.

一定要检查链接,还有更多我不能引用的东西。

其他回答

If you are still confused, here is a very simple way of understanding a co-routine. First off, what is a routine? In a lay man's term, a routine is something that we do again and again (for example, your morning routine). Similarly. in programming languages, a routine is a piece of code that we use again and again, e.g., a function. Now, if you look at the general characteristic of a function or routine (note: I am cautiously using these two terms interchangeably), it takes some inputs and hogs the CPU threads for as long as the function needs to output the result. Meaning, functions or routines are blocking calls in you code. However, a co-routine is a special kind of routine that can co-exist (the "co" part of the word co-routine comes from this) with other routines at the same time and we can make this happen in programming languages with the help of asynchronous programming. In Asynchronous programming, when one co-routine is waiting for something to happen (e.g., disk io), the other co-routine will start working and when this co-routine is in a waiting state the other co-routine will be active ultimately reducing the waiting time of our code.

如果你理解了上面的内容,让我们看看如何在Python中创建协程函数。可以像下面那样定义协程函数-

async def my_coroutine_function():
    return 123

你可以通过在协同程序-前面添加await来调用上面的协同程序

my_result = await my_coroutine_function()

最后,

当你正在看电视节目,广告一出现,你就拿起手机给朋友发短信——你刚刚做的就是异步编程。当你的电视节目(一个合作程序)处于等待状态时,你继续前进,让你的另一个合作程序(给你的朋友发短信)处于激活状态。

协程作为并发性的实现和多线程的替代方案。

协程是实现并发的单线程解决方案。

         A-Start ------------------------------------------ A-End   
           | B-Start -----------------------------------------|--- B-End   
           |    |      C-Start ------------------- C-End      |      |   
           |    |       |                           |         |      |
           V    V       V                           V         V      V      
1 thread->|<-A-|<--B---|<-C-|-A-|-C-|--A--|-B-|--C-->|---A---->|--B-->| 

与多线程解决方案相比:

thread A->|<--A|          |--A-->|
thread B------>|<--B|            |--B-->|
thread C ---------->|<---C|             |C--->|

协程是异步编程的一种实现,异步编程用于实现并发。 许多语言使用协程实现异步编程。其他答案表明Python, Kotlin, Lua, c++已经做到了。 最有用/通常用于涉及I/O绑定问题的场景,例如在获取数据时呈现UI,或从多个数据源下载。

协程和并发在很大程度上是正交的。协程是一种通用的控制结构,流控制在两个不同的例程之间协作传递而不返回。

Python中的'yield'语句就是一个很好的例子。它创建了一个协程。当遇到yield时,将保存函数的当前状态,并将控制返回给调用函数。然后,调用函数可以将执行转移回屈服函数,它的状态将恢复到遇到“屈服”的位置,并继续执行。

我将详述@user21714的答案。协程是独立的执行路径,不能同时运行。它们依赖于一个控制器(例如python控制器库)来处理这些路径之间的切换。但是为了实现这一点,协同程序本身需要调用yield或类似的结构,以允许它们的执行暂停。

相反,线程运行在独立的计算资源上,并且彼此并行。由于它们位于不同的资源上,因此不需要调用yield来允许其他执行路径继续进行。

您可以通过启动一个多线程程序(例如jvm应用程序)来看到这种效果,其中所有八个核心i7超线程核心都被利用了:您可能会在Activity Monitor或Top中看到797%的利用率。相反,当运行一个典型的python程序(即使是带有协程或python线程的程序)时,利用率最高将达到100%。例如,一台机器超线程。

协程类似于子例程/线程。 区别在于,一旦调用方调用了子例程/线程,它将永远不会返回到调用方函数。 但是协程可以在执行几段代码后返回到调用方,允许调用方执行一些自己的代码,并返回到它停止执行的协程点,并从那里继续。 ie。协程有多个入口点和出口点