flask 源碼淺析(flask 如何處理請求(多線程，多進程，IO多路復用))

 

2018-04-04 13:09:47 lucky404 閱讀數 5724更多

分類專欄： python

 

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本文鏈接： https://blog.csdn.net/lucky404/article/details/79815997

之前有閱讀過tornado 底層的實現，tornado 為了解決C10K 問題(沒聽說過C10K問題的請查看: http://www.360doc.com/content/13/0522/18/1542811_287328391.shtml)，在Linux 平台下是使用了epoll（python2.6 開始支持epoll），unix 平台下 tornado 使用了kque , 由於flask 之前沒有看過底層的實現，因此趁着清明假期看了一下flask，到底是來一個請求使用一個線程呢，還是進程呢，還是IO多路復用。

涉及到的源碼文件

site-packages/flask/app.py, site-packages/werkzeug/serving.py, Lib/socketserver.py

首先肯定要先看入口函數啦

app.py 里面的 run 函數

def run(self, host=None, port=None, debug=None, **options):

該函數通過 run_simple(host, port, self, **options) 啟動了socket 服務器(無論是哪個web框架，其實底層都是使用socketserver 監聽在某個套接字上來處理請求的)

run_simple 然后到調用 serving.py 里面的make_server

make_server 源碼定義如下:

def make_server(host=None, port=None, app=None, threaded=False, processes=1, request_handler=None, passthrough_errors=False, ssl_context=None, fd=None): """Create a new server instance that is either threaded, or forks or just processes one request after another. """ if threaded and processes > 1: raise ValueError("cannot have a multithreaded and " "multi process server.") elif threaded: return ThreadedWSGIServer(host, port, app, request_handler, passthrough_errors, ssl_context, fd=fd) elif processes > 1: return ForkingWSGIServer(host, port, app, processes, request_handler, passthrough_errors, ssl_context, fd=fd) else: return BaseWSGIServer(host, port, app, request_handler, passthrough_errors, ssl_context, fd=fd)

可以看到flask 為我們提供了三種方式來處理請求
1 使用多線程來進行處理
2 使用多進程來進行處理
3 使用poll 或者 select IO多路復用的方式進行處理

BaseWSGIServer 這個類是使用IO 多路復用的
下面有個方法 start_forever

    def serve_forever(self): self.shutdown_signal = False try: HTTPServer.serve_forever(self) except KeyboardInterrupt: pass finally: self.server_close()

我們主要來看HttpServer.serve_forever方法

 def serve_forever(self, poll_interval=0.5): """Handle one request at a time until shutdown. Polls for shutdown every poll_interval seconds. Ignores self.timeout. If you need to do periodic tasks, do them in another thread. """ self.__is_shut_down.clear() try: # XXX: Consider using another file descriptor or connecting to the # socket to wake this up instead of polling. Polling reduces our # responsiveness to a shutdown request and wastes cpu at all other # times. with _ServerSelector() as selector: selector.register(self, selectors.EVENT_READ) while not self.__shutdown_request: ready = selector.select(poll_interval) if ready: self._handle_request_noblock() self.service_actions() finally: self.__shutdown_request = False self.__is_shut_down.set()

_ServerSelector() 定義了 到底該使用select 還是 poll

# poll/select have the advantage of not requiring any extra file descriptor, # contrarily to epoll/kqueue (also, they require a single syscall). if hasattr(selectors, 'PollSelector'): _ServerSelector = selectors.PollSelector else: _ServerSelector = selectors.SelectSelector

對於IO多路復用不熟悉的，推薦查看該文章: https://blog.csdn.net/qq546770908/article/details/53082870