【Python之路】异步IO

线程：CPU基本执行单元，可以与同属一个进程的其他线程共享资源，线程是属于进程的。

进程：资源单元，进程一般由程序、数据集、进程控制块三部分组成。一个进程默认有一个主线程，

GIL：用于在进程中对所有线程加锁，同一时刻只有一个线程被cpu调度。GIL对IO请求影响小。

在编写爬虫时，性能的消耗主要在IO请求中

当单线程模式下请求URL时必然会引起等待，从而使得请求整体变慢。

import requests
 
def fetch_async(url):
 
    response = requests.get(url)
    print(response.text)
    return response
 
if __name__ == '__main__':
 
    url_list = ['http://www.github.com', 'http://www.bing.com']
 
    for url in url_list:
        fetch_async(url)

同步执行

多线程方式运行：

import requests
from concurrent.futures import ThreadPoolExecutor
 
def fetch_async(url):
 
    response = requests.get(url)
    return response
 
if __name__ == '__main__':
 
    pool = ThreadPoolExecutor(5)
 
    url_list = ['http://www.github.com', 'http://www.bing.com']
 
    for url in url_list:
        pool.submit(fetch_async,url)
 
    pool.shutdown()

多线程

import requests
from concurrent.futures import ThreadPoolExecutor
 
def fetch_async(url):
 
    response = requests.get(url)
    return response
 
def callback(future):
    print(future.result())
 
if __name__ == '__main__':
 
    pool = ThreadPoolExecutor(5)
 
    url_list = ['http://www.github.com', 'http://www.bing.com']
 
    for url in url_list:
        v = pool.submit(fetch_async,url)
        v.add_done_callback(callback)
 
    pool.shutdown()

多线程+回调函数

多进程方式运行:

import requests
from concurrent.futures import ProcessPoolExecutor
 
def fetch_async(url):
 
    response = requests.get(url)
    return response
 
if __name__ == '__main__':
 
    pool = ProcessPoolExecutor(5)
 
    url_list = ['http://www.github.com', 'http://www.bing.com']
 
    for url in url_list:
        pool.submit(fetch_async,url)
 
    pool.shutdown(wait=True)

多进程

import requests
from concurrent.futures import ProcessPoolExecutor
 
def fetch_async(url):
 
    response = requests.get(url)
    return response
 
def callback(future):
    print(future.result())
 
if __name__ == '__main__':
 
    pool = ProcessPoolExecutor(5)
 
    url_list = ['http://www.github.com', 'http://www.bing.com']
 
    for url in url_list:
        v = pool.submit(fetch_async,url)
        v.add_done_callback(callback)
 
    pool.shutdown(wait=True)

多进程+回调函数

通过上述代码均可以完成对请求性能的提高，对于多线程和多进行的缺点是在IO阻塞时会造成了线程和进程的浪费，所以异步IO会是首选：

import asyncio
 
@asyncio.coroutine
def func1():
    print('before...func1......')
    yield from asyncio.sleep(5)
    print('end...func1......')
 
tasks = [func1(), func1()]
 
loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

asyncio-示例1

异步发送TCP请求:

import asyncio
 
@asyncio.coroutine
def fetch_async(host, url='/'):
    print(host, url)
    reader, writer = yield from asyncio.open_connection(host, 80)
 
    request_header_content = """GET %s HTTP/1.0\r\nHost: %s\r\n\r\n""" % (url, host,)
    request_header_content = bytes(request_header_content, encoding='utf-8')
 
    writer.write(request_header_content)
    yield from writer.drain()
    text = yield from reader.read()
    print(host, url, text)
    writer.close()
 
tasks = [
    fetch_async('www.cnblogs.com', '/alex/'),
    fetch_async('dig.chouti.com', '/pic/show?nid=4073644713430508&lid=10273091')
]
 
loop = asyncio.get_event_loop()
results = loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

asyncio-示例2

import asyncio
from aiohttp import ClientSession
 
async def func1(url):
    print(url)
    async with ClientSession() as session:
        async with session.get(url) as response:
            response = await response.read()
            print('Response OK')
 
tasks = [
    asyncio.ensure_future(func1('https://www.cnblogs.com/')),
    asyncio.ensure_future(func1('https://www.baidu.com/')),
    asyncio.ensure_future(func1('https://www.python.org/')),
]
 
loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.gather(*tasks))

asyncio + aiohttp

import asyncio
import requests
 
@asyncio.coroutine
def fetch_async(func, *args):
    loop = asyncio.get_event_loop()
    future = loop.run_in_executor(None, func, *args)
    response = yield from future
    print(response.url, response.content)
 
tasks = [
    fetch_async(requests.get, 'http://www.cnblogs.com/alex/'),
    fetch_async(requests.get, 'http://dig.chouti.com/pic/show?nid=4073644713430508&lid=10273091')
]
 
loop = asyncio.get_event_loop()
results = loop.run_until_complete(asyncio.gather(*tasks))
loop.close()

asyncio + requests

import gevent
 
import requests
from gevent import monkey
 
monkey.patch_all()
 
def fetch_async(method, url, req_kwargs):
    print(method, url, req_kwargs)
    response = requests.request(method=method, url=url, **req_kwargs)
    print(response.url, response.content)
 
# ##### 发送请求 #####
gevent.joinall([
    gevent.spawn(fetch_async, method='get', url='https://www.python.org/', req_kwargs={}),
    gevent.spawn(fetch_async, method='get', url='https://www.yahoo.com/', req_kwargs={}),
    gevent.spawn(fetch_async, method='get', url='https://github.com/', req_kwargs={}),
])
 
# ##### 发送请求（协程池控制最大协程数量） #####
# from gevent.pool import Pool
# pool = Pool(None)
# gevent.joinall([
#     pool.spawn(fetch_async, method='get', url='https://www.python.org/', req_kwargs={}),
#     pool.spawn(fetch_async, method='get', url='https://www.yahoo.com/', req_kwargs={}),
#     pool.spawn(fetch_async, method='get', url='https://www.github.com/', req_kwargs={}),
# ])

gevent + requests

import grequests
 
request_list = [
    grequests.get('http://httpbin.org/delay/1', timeout=0.001),
    grequests.get('http://fakedomain/'),
    grequests.get('http://httpbin.org/status/500')
]
 
# ##### 执行并获取响应列表 #####
# response_list = grequests.map(request_list)
# print(response_list)
 
# ##### 执行并获取响应列表（处理异常） #####
# def exception_handler(request, exception):
# print(request,exception)
#     print("Request failed")
 
# response_list = grequests.map(request_list, exception_handler=exception_handler)
# print(response_list)

grequests

from twisted.web.client import getPage
from twisted.internet import reactor
 
REV_COUNTER = 0
REQ_COUNTER = 0
 
def callback(contents):
    print(contents,)
 
    global REV_COUNTER
    REV_COUNTER += 1
    if REV_COUNTER == REQ_COUNTER:
        reactor.stop()
 
url_list = ['http://www.bing.com', 'http://www.baidu.com', ]
REQ_COUNTER = len(url_list)
for url in url_list:
    print(url)
    deferred = getPage(bytes(url, encoding='utf8'))
    deferred.addCallback(callback)
reactor.run()

twisted-示例1

from twisted.internet import reactor
from twisted.web.client import getPage
import urllib.parse
 
def one_done(arg):
    print(arg)
    reactor.stop()
 
post_data = urllib.parse.urlencode({'check_data': 'adf'})
post_data = bytes(post_data, encoding='utf8')
headers = {b'Content-Type': b'application/x-www-form-urlencoded'}
response = getPage(bytes('http://dig.chouti.com/login', encoding='utf8'),
                   method=bytes('POST', encoding='utf8'),
                   postdata=post_data,
                   cookies={},
                   headers=headers)
response.addBoth(one_done)
 
reactor.run()

twisted-示例2

from tornado.httpclient import AsyncHTTPClient
from tornado.httpclient import HTTPRequest
from tornado import ioloop
 
def handle_response(response):
    """
    处理返回值内容（需要维护计数器，来停止IO循环），调用 ioloop.IOLoop.current().stop()
    :param response:
    :return:
    """
    if response.error:
        print("Error:", response.error)
    else:
        print(response.body)
 
def func():
    url_list = [
        'http://www.baidu.com',
        'http://www.bing.com',
    ]
    for url in url_list:
        print(url)
        http_client = AsyncHTTPClient()
        http_client.fetch(HTTPRequest(url), handle_response)
 
ioloop.IOLoop.current().add_callback(func)
ioloop.IOLoop.current().start()

tornado

以上均是Python内置以及第三方模块提供异步IO请求模块，使用简便大大提高效率，而对于异步IO请求的本质则是【非阻塞Socket】+【IO多路复用】：

import select
import socket
import time
 
class AsyncTimeoutException(TimeoutError):
    """
    请求超时异常类
    """
 
    def __init__(self, msg):
        self.msg = msg
        super(AsyncTimeoutException, self).__init__(msg)
 
class HttpContext(object):
    """封装请求和相应的基本数据"""
 
    def __init__(self, sock, host, port, method, url, data, callback, timeout=5):
        """
        sock: 请求的客户端socket对象
        host: 请求的主机名
        port: 请求的端口
        port: 请求的端口
        method: 请求方式
        url: 请求的URL
        data: 请求时请求体中的数据
        callback: 请求完成后的回调函数
        timeout: 请求的超时时间
        """
        self.sock = sock
        self.callback = callback
        self.host = host
        self.port = port
        self.method = method
        self.url = url
        self.data = data
 
        self.timeout = timeout
 
        self.__start_time = time.time()
        self.__buffer = []
 
    def is_timeout(self):
        """当前请求是否已经超时"""
        current_time = time.time()
        if (self.__start_time + self.timeout) < current_time:
            return True
 
    def fileno(self):
        """请求sockect对象的文件描述符，用于select监听"""
        return self.sock.fileno()
 
    def write(self, data):
        """在buffer中写入响应内容"""
        self.__buffer.append(data)
 
    def finish(self, exc=None):
        """在buffer中写入响应内容完成，执行请求的回调函数"""
        if not exc:
            response = b''.join(self.__buffer)
            self.callback(self, response, exc)
        else:
            self.callback(self, None, exc)
 
    def send_request_data(self):
        content = """%s %s HTTP/1.0\r\nHost: %s\r\n\r\n%s""" % (
            self.method.upper(), self.url, self.host, self.data,)
 
        return content.encode(encoding='utf8')
 
class AsyncRequest(object):
    def __init__(self):
        self.fds = []
        self.connections = []
 
    def add_request(self, host, port, method, url, data, callback, timeout):
        """创建一个要请求"""
        client = socket.socket()
        client.setblocking(False)
        try:
            client.connect((host, port))
        except BlockingIOError as e:
            pass
            # print('已经向远程发送连接的请求')
        req = HttpContext(client, host, port, method, url, data, callback, timeout)
        self.connections.append(req)
        self.fds.append(req)
 
    def check_conn_timeout(self):
        """检查所有的请求，是否有已经连接超时，如果有则终止"""
        timeout_list = []
        for context in self.connections:
            if context.is_timeout():
                timeout_list.append(context)
        for context in timeout_list:
            context.finish(AsyncTimeoutException('请求超时'))
            self.fds.remove(context)
            self.connections.remove(context)
 
    def running(self):
        """事件循环，用于检测请求的socket是否已经就绪，从而执行相关操作"""
        while True:
            r, w, e = select.select(self.fds, self.connections, self.fds, 0.05)
 
            if not self.fds:
                return
 
            for context in r:
                sock = context.sock
                while True:
                    try:
                        data = sock.recv(8096)
                        if not data:
                            self.fds.remove(context)
                            context.finish()
                            break
                        else:
                            context.write(data)
                    except BlockingIOError as e:
                        break
                    except TimeoutError as e:
                        self.fds.remove(context)
                        self.connections.remove(context)
                        context.finish(e)
                        break
 
            for context in w:
                # 已经连接成功远程服务器，开始向远程发送请求数据
                if context in self.fds:
                    data = context.send_request_data()
                    context.sock.sendall(data)
                    self.connections.remove(context)
 
            self.check_conn_timeout()
 
if __name__ == '__main__':
    def callback_func(context, response, ex):
        """
        :param context: HttpContext对象，内部封装了请求相关信息
        :param response: 请求响应内容
        :param ex: 是否出现异常（如果有异常则值为异常对象；否则值为None）
        :return:
        """
        print(context, response, ex)
 
    obj = AsyncRequest()
    url_list = [
        {'host': 'www.google.com', 'port': 80, 'method': 'GET', 'url': '/', 'data': '', 'timeout': 5,
         'callback': callback_func},
        {'host': 'www.baidu.com', 'port': 80, 'method': 'GET', 'url': '/', 'data': '', 'timeout': 5,
         'callback': callback_func},
        {'host': 'www.bing.com', 'port': 80, 'method': 'GET', 'url': '/', 'data': '', 'timeout': 5,
         'callback': callback_func},
    ]
    for item in url_list:
        print(item)
        obj.add_request(**item)
 
    obj.running()

自定义异步IO