coroutine 协程

原创

vanguard

修改于 2020-03-20 17:53:38

4670

修改于 2020-03-20 17:53:38

文章被收录于专栏：vanguard

Coroutines are computer-program components that generalize subroutines for non-preemptive multitasking, by allowing multiple entry points for suspending and resuming execution at certain locations. Coroutines are well-suited for implementing familiar program components such as cooperative tasks, exceptions, event loops, iterators, infinite lists and pipes. The async def type of coroutine was added in Python 3.5, and is recommended if there is no need to support older Python versions.

由于GIL的存在，导致Python多线程性能甚至比单线程更糟。

GIL: 全局解释器锁（英语：Global Interpreter Lock，缩写GIL），是计算机程序设计语言解释器用于同步线程的一种机制，它使得任何时刻仅有一个线程在执行。[1]即便在多核心处理器上，使用 GIL 的解释器也只允许同一时间执行一个线程。

于是出现了协程（Coroutine）这么个东西。

协程/微线程/纤程/Coroutine作用是在执行函数A时，可以随时中断，去执行函数B，然后中断继续执行函数A（可以自由切换）。但这一过程并不是函数调用（没有调用语句），这一整个过程看似像多线程，然而协程只有一个线程执行。

import asyncio

async def compute(x, y):
    print("Compute %s + %s ..." % (x, y))
    await asyncio.sleep(1.0)
    return x + y

async def print_sum(x, y):
    result = await compute(x, y)
    print("%s + %s = %s" % (x, y, result))

loop = asyncio.get_event_loop()
loop.run_until_complete(print_sum(1, 2))
loop.close()

Compute 1 + 2 ...
1 + 2 = 3
[Finished in 1.2s]

import asyncio

async def factorial(name, number):
    f = 1
    for i in range(2, number+1):
        print("Task %s: Compute factorial(%s)..." % (name, i))
        await asyncio.sleep(1)
        f *= i
    print("Task %s: factorial(%s) = %s" % (name, number, f))

loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.gather(
    factorial("A", 2),
    factorial("B", 3),
    factorial("C", 4),
))
loop.close()

Task B: Compute factorial(2)...
Task A: Compute factorial(2)...
Task C: Compute factorial(2)...
Task B: Compute factorial(3)...
Task A: factorial(2) = 2
Task C: Compute factorial(3)...
Task B: factorial(3) = 6
Task C: Compute factorial(4)...
Task C: factorial(4) = 24
[Finished in 3.2s]

https://docs.python.org/zh-cn/3/library/asyncio-task.html

https://juejin.im/post/5c13245ee51d455fa5451f33

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