时间循环 asyncio 协程

Posted 2020-12-21 dissipate

　　

事件循环是asyncio提供的核心运行机制

column	column
asyncio.get_event_loop()	返回一个事件循环对象,时asyncio.BaseEventLoop的实例
AbstractEventLoop.stop()	停止运行事件循环
AbstractEventLoop.run_forever()	一直运行,直到stop()
AbstractEventLoop.run_until_complete(future)	运行直至future对象运行完
AbstractEventLoop.close()	关闭事件循环对象
AbstractEventLoop.is_running()	返回事件循环对象是否运行
Abstract Event Loop.close()	关闭事件循环

 

协程:

协程是用户空间调度完成并发处理的方式

进程,线程由OS完成调度,而协程是线程内完成调度,它不需要更多线程,没有多线程切换带来的开销

协程是非抢占式调度,只有一个协程主动让出控制权,另一个协程才会被调度

协程也不需要使用锁机制,因为是在同一线程中执行

多CPU下,可以使用多进程和协程配合,既能 进程并发又能发挥协程在单线程中的优势

python中协程是基于生成器的

协程的使用:

import asyncio

async def sleep(b):
    for i in range(3):
        print(‘sleep {}‘.format(i))
        await asyncio.sleep(i)

loop=asyncio.get_event_loop()
loop.run_until_complete(sleep(3))
loop.close()

　　

async def 用来定义协程函数,iscoroutinefunction()返回True,协程函数中可以不包含await async关键字,但是不能使用yield关键字

如同生成器函数调用返回生成器对象,协程函数调用也会返回一个对象称为协程对象,

iscoroutine()返回True

iscoroutinefunction()

import asyncio,threading
async def sleep(b):
    for v in range(3):
        print(‘sleep {}‘.format(v))
        await asyncio.sleep(b)
async def show():
    for _ in range(3):
        print(threading.enumerate())
        await asyncio.sleep(2)
print(asyncio.iscoroutinefunction(sleep))
print(asyncio.iscoroutine(sleep))
print(asyncio.iscoroutine(sleep(3)))
loop=asyncio.get_event_loop()
tasks=[sleep(3),show()]
loop.run_until_complete(asyncio.wait(tasks))
loop.close()

 

TCP Echo Server

import asyncio

async def handle(reader,writer):
    while True:
        datum=await reader.read(1024)
        print(dir(reader))
        print(dir(writer))
        client=writer.get_extra_info(‘peername‘)
        message=‘{} = {}‘.format(client,datum.decode()).encode()
        writer.write(message)
        await writer.drain()

loop=asyncio.get_event_loop()
crt=asyncio.start_server(handle,‘‘,9999,loop=loop)

server=loop.run_until_complete(crt)
print(server)

try:
    loop.run_forever()
except KeyboardInterrupt:
    pass
finally:
    server.close()
    loop.close()

 

aiohttp

HTTP Server

from aiohttp import web
async def indexhandle(request:web.Request):
    return web.Response(text=request.path,status=201)

async def handle(request:web.Request):
    print(request.match_info)
    print(request.query_string)
    return web.Response(text=request.match_info.get(‘id‘,‘000‘),status=200)

app=web.Application()
app.router.add_get(‘/‘,indexhandle)
app.router.add_get(‘/{id}‘,handle)

web.run_app(app,host=‘0.0.0.0‘,port=9988)

　　

HTTP Client

import asyncio
from aiohttp import ClientSession
async def get_html(url:str):
    async with ClientSession() as session:
        async with session.get(url) as res:
            print(res.status)
            print(await res.text())

url=‘http://www.baidu.com‘
loop=asyncio.get_event_loop()
loop.run_until_complete(get_html(url))
loop.close()