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  • 【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

    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
    Host: %s
    
    """ % (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
    Host: %s
    
    %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
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  • 原文地址:https://www.cnblogs.com/5poi/p/8268806.html
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