Co process, asyncio, asynchronous programming

1 coroutines

The coroutine is not provided by the operating system , Provided by programmers （ User state context switching technology ）

Coinciding （Coroutine）, It can also be called a microthread , It's a context switch technology in user mode . In short , In fact, code blocks are switched and executed through a thread .

Several methods of realizing collaborative process ：

• greenlet、 Early modules
• yield keyword
• asynco Decorator (py3.4)
• async、await keyword (py3.5)( recommend )

The significance of synergy
In a thread , If you encounter IO Waiting time , Threads don't wait , Use your spare time to do other things .

2 Asynchronous programming

3.1 The event loop

Understanding micro is an endless cycle , To detect and execute some code

import asyncio

#  Generate or get an event loop 
loop = asyncio.get_event_loop()

#  Put the task on   Task list 
loop.run_until_complete( Mission )

3.2 async

Coroutines function ： When defining a function async def Function name
Coroutine object ： Execute the coprogram function () Get the collaboration object

#  Coroutine object 
async def func():
	pass	#  Content not executed 

#  Coroutine object 
result = func()

Be careful ： Execute the coroutine function to create the love coroutine object , Function internal code will not execute

Event loop handler internal code

import asyncio

#  Coroutine object 
async def func():
	pass	#  Content not executed 

#  Coroutine object 
result = func()

#  Add event , Help execute function internal code  py3.4
#loop = asyncio.get_event_loop()
#loop.run_until_complete(result)

# py3.7
asycio.run(result)

3.3 await

await + Can wait for the object （ Coroutine object 、Future、Task）

await Is to wait for the value of the object to get the result, and then continue to move forward

Case a ：

import asyncio

async def func():
    print("666")
    #  Wait here 2 second , There are other tasks to perform other tasks , Then continue to execute backward 
    res = await asyncio.sleep(2)
    print(" end ", res)

asyncio.run(func())

Case 2 ：

import asyncio

async def others():
    print("start")
    await asyncio.sleep(2)
    print("end")
    return " Return value "

async def func():
    print(" Execute the internal code of the coroutine function ")

    #  encounter IO Operation suspends the current orchestration （ Mission ）, etc. IO After the operation is completed, continue to execute .
    #  When the current schedule is suspended , The event loop can be used to execute other coroutines （ Mission ）
    res = await others()
    print("IO End of request , The result is ：", res)
    
asyncio.run(func())

Case three

import asyncio


async def others():
    print("start")
    await asyncio.sleep(2)
    print("end")
    return " Return value "


async def func():
    print(" Execute the internal code of the coroutine function ")

    #  encounter IO Operation suspends the current orchestration （ Mission ）, etc. IO After the operation is completed, continue to execute .
    #  When the current schedule is suspended , The event loop can be used to execute other coroutines （ Mission ）
    res1 = await others()
    print("IO End of request , The result is ：", res1)

    res2 = await others()
    print("IO End of request , The result is ：", res2)

asyncio.run(func())

3.4 Task object

• py3.7

• Add multiple tasks to the event loop

• Task For concurrent scheduling coroutines , adopt asyncio.create_task( Coroutine object ) The way to create love for you Task object , This allows the coroutine to join the event loop and wait for the scheduled execution . Besides using asyncio.create_task() Function , You can also use lower level loop_create_task() or ensure_future() function . Manual instantiation is not recommended Task object .

Reference address ：
https://www.bilibili.com/video/BV1dD4y127bD