Python?Django源碼運(yùn)行過(guò)程解析

更新時(shí)間：2022年08月20日 15:30:20 作者：黑日里不滅的light

這篇文章主要介紹了Python?Django源碼運(yùn)行過(guò)程，本文給大家介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或工作具有一定的參考借鑒價(jià)值,需要的朋友可以參考下

一、Django運(yùn)行順序

WSGI會(huì)不斷監(jiān)聽(tīng)客戶端發(fā)送來(lái)的請(qǐng)求
先經(jīng)過(guò)中間件進(jìn)行分析驗(yàn)證處理
然后經(jīng)過(guò)url分發(fā)與驗(yàn)證
視圖層進(jìn)行處理
再經(jīng)過(guò)中間件進(jìn)行分析驗(yàn)證處理
返回響應(yīng)內(nèi)容

1.啟動(dòng)

1.1 命令行啟動(dòng)(測(cè)試服務(wù)器)

命令行結(jié)論：其在第二步utility.execute()函數(shù)會(huì)根據(jù)命令行參數(shù)，分發(fā)給不同的類進(jìn)行處理

在manange.py里面execute_from_command_line(sys.argv)進(jìn)入關(guān)鍵代碼

def main():
    os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'testDjango.settings')
    try:
        from django.core.management import execute_from_command_line
    except ImportError as exc:
		---
    execute_from_command_line(sys.argv)

2.execute_from_command_line函數(shù)里面其實(shí)例化 ManagementUtility類然后執(zhí)行utility.execute()函數(shù) [
2.1. 此函數(shù)是專門(mén)用來(lái)分析參數(shù)的，例如python manage.py runserver、python manage.py help
2.2 其會(huì)通過(guò)分析額外添加的參數(shù)選擇要使用的類或者函數(shù)，類或者函數(shù)對(duì)應(yīng)著django\core\management\commands里面的類

def execute_from_command_line(argv=None):
    utility = ManagementUtility(argv)
    utility.execute()

3.從self.fetch_command(subcommand).run_from_argv(self.argv)[約第413行]
3.1 self.fetch_command(subcommand)，這個(gè)函數(shù)返回了runserver.Command對(duì)象（可以自行深入查看），之后執(zhí)行該Command父類里面的run_from_argv函數(shù)

 def execute(self):
			---
        if subcommand == 'help':
			---
        elif subcommand == 'version' or self.argv[1:] == ['--version']:
            sys.stdout.write(django.get_version() + '\n')
        elif self.argv[1:] in (['--help'], ['-h']):
            sys.stdout.write(self.main_help_text() + '\n')
        else:
            self.fetch_command(subcommand).run_from_argv(self.argv)

4.從run_from_argv函數(shù)self.execute(*args, **cmd_options)進(jìn)入
4.1 當(dāng)前類也有這個(gè)execute函數(shù)，但是由于繼承關(guān)系（此時(shí)的self也指向Command類），子類如果已經(jīng)存在該函數(shù)會(huì)覆蓋執(zhí)行，execute是在子類 Command類中（之后由于super還會(huì)到父類里面）[約第354行]

    def run_from_argv(self, argv):
        self._called_from_command_line = True
        parser = self.create_parser(argv[0], argv[1])
        options = parser.parse_args(argv[2:])
        cmd_options = vars(options)

        args = cmd_options.pop('args', ())
        handle_default_options(options)
        try:
            self.execute(*args, **cmd_options)
        except CommandError as e:
			---

5.execute函數(shù)執(zhí)行output = self.handle(*args, **options)[約第398行]跳進(jìn)子類runserver.Command類的handle函數(shù)
5.1 此時(shí)位于Command類的父類里面的execute，因?yàn)?code>super().execute(*args, **options) #繼承下來(lái)父類

    def handle(self, *args, **options):
        if not settings.DEBUG and not settings.ALLOWED_HOSTS:
            raise CommandError('You must set settings.ALLOWED_HOSTS if DEBUG is False.')
        self.use_ipv6 = options['use_ipv6']
        if self.use_ipv6 and not socket.has_ipv6:
            raise CommandError('Your Python does not support IPv6.')
        self._raw_ipv6 = False
        if not options['addrport']:
        	---
        else:
           	---
        if not self.addr:
            self.addr = self.default_addr_ipv6 if self.use_ipv6 else self.default_addr
            self._raw_ipv6 = self.use_ipv6
        self.run(**options)

6.handle 函數(shù)最后一行，從 self.run(**options) 進(jìn)入

    def run(self, **options):
        use_reloader = options['use_reloader']

        if use_reloader:
            autoreload.run_with_reloader(self.inner_run, **options)
        else:
            self.inner_run(None, **options)

7.從def inner_run(self, *args, \*\*options)再執(zhí)行run函數(shù)

    def inner_run(self, *args, **options):
    		---
        try:
            handler = self.get_handler(*args, **options)
            run(self.addr, int(self.port), handler,
                ipv6=self.use_ipv6, threading=threading, server_cls=self.server_cls)
        except OSError as e:
          	 ---

8.最后啟動(dòng)服務(wù)，此時(shí)跳到django.core.servers.basehttp.py的run函數(shù)
8.1 httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), {}) 這一步特別重要，其涉及到較長(zhǎng)的繼承關(guān)系，2.監(jiān)聽(tīng)-4.1這一環(huán)節(jié)會(huì)介紹到

def run(addr, port, wsgi_handler, ipv6=False, threading=False, server_cls=WSGIServer):
    server_address = (addr, port)
    if threading:
        httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), {})
    else:
        httpd_cls = server_cls
    httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)
    if threading:
        httpd.daemon_threads = True
    httpd.set_app(wsgi_handler)
    httpd.serve_forever()

總結(jié)流程：

解析運(yùn)行 python manage.py 所提供的參數(shù)，例如: help
加載所有的app
根據(jù)參數(shù)找到相對(duì)應(yīng)的命令管理工具
檢查端口、ipv4檢測(cè)、ipv6檢測(cè)、端口是否占用、線程檢查
orm對(duì)象檢查表是否創(chuàng)建
最后啟動(dòng)python Lib庫(kù)中的WSGIServer

2.監(jiān)聽(tīng)

解釋：WSGI開(kāi)啟后，不間斷的監(jiān)聽(tīng)外界的請(qǐng)求

快速閱讀：下面寫(xiě)的比較麻煩，最快了解監(jiān)聽(tīng)和到中間件前的經(jīng)過(guò)就是去讀 1 、12.1 和 13

2.1 runserver(測(cè)試服務(wù)器)

1.runserver成功開(kāi)啟后，關(guān)鍵的一步是httpd.serve_forever()，其使得進(jìn)入監(jiān)聽(tīng)即一個(gè)死循環(huán)

def run(addr, port, wsgi_handler, ipv6=False, threading=False, server_cls=WSGIServer):
	---
    httpd.set_app(wsgi_handler)
    httpd.serve_forever()

2.在serve_forever()函數(shù)里面執(zhí)行，當(dāng)ready有值時(shí)，表示有請(qǐng)求發(fā)來(lái)，然后進(jìn)入self._handle_request_noblock()

    def serve_forever(self, poll_interval=0.5):
        self.__is_shut_down.clear()
        try:
            with _ServerSelector() as selector:
                selector.register(self, selectors.EVENT_READ)
                while not self.__shutdown_request:
                    ready = selector.select(poll_interval)
                    if self.__shutdown_request:
                        break
                    if ready:
                        self._handle_request_noblock()

                    self.service_actions()
		---

3.從self._handle_request_noblock()正常請(qǐng)求將進(jìn)入self.process_request(request, client_address)

    def _handle_request_noblock(self):
        try:
            request, client_address = self.get_request()
        except OSError:
            return
        if self.verify_request(request, client_address):
            try:
                self.process_request(request, client_address)
            except Exception:
                self.handle_error(request, client_address)
                self.shutdown_request(request)
            except:
                self.shutdown_request(request)
                raise
        else:
            self.shutdown_request(request)

4.從self.process_request(request, client_address)進(jìn)入來(lái)到了ThreadingMixIn.process_request
4.1 此時(shí)，如果沒(méi)有搞清楚此時(shí)的self是誰(shuí)，就搞不明白為什么進(jìn)入到ThreadingMixIn.process_request，而不是其它的process_request，這時(shí)候就關(guān)聯(lián)到上面提到的httpd_cls = type('WSGIServer', (socketserver.ThreadingMixIn, server_cls), {})
4.2 type的用法是動(dòng)態(tài)的創(chuàng)建類，此時(shí)httpd_cls 是一個(gè)新類，里面分別繼承了ThreadingMixIn和server_cls對(duì)應(yīng)得WSGIServer，這時(shí)就不難理解為什么找的是ThreadingMixIn.process_request

    def process_request(self, request, client_address):
        """Start a new thread to process the request."""
        t = threading.Thread(target = self.process_request_thread,
                             args = (request, client_address))
        t.daemon = self.daemon_threads
        if not t.daemon and self.block_on_close:
            if self._threads is None:
                self._threads = []
            self._threads.append(t)
        t.start()

5.在def process_request(self, request, client_address)里面的t = threading.Thread(target = self.process_request_thread,args = (request, client_address))實(shí)際調(diào)用了self.process_request_thread，但是等t.start()才會(huì)真正執(zhí)行

    def process_request_thread(self, request, client_address):
        """Same as in BaseServer but as a thread.

        In addition, exception handling is done here.

        """
        try:
            self.finish_request(request, client_address)
        except Exception:
            self.handle_error(request, client_address)
        finally:
            self.shutdown_request(request)

6.從def process_request_thread(self, request, client_address)進(jìn)入，self.finish_request(request, client_address)，繼續(xù)完成請(qǐng)求
6.1 這時(shí)候又需要回顧之前的代碼，因?yàn)?code>self.RequestHandlerClass不是已經(jīng)有的類，而是初始化的時(shí)候賦值，其值變?yōu)榱四硞€(gè)類
6.2 這個(gè)過(guò)程就在1.啟動(dòng)-8里面的httpd = httpd_cls(server_address, WSGIRequestHandler, ipv6=ipv6)，此時(shí)的httpd_cls是type動(dòng)態(tài)創(chuàng)建的，繼承了ThreadingMixIn和server_cls對(duì)應(yīng)得WSGIServer，實(shí)例化時(shí)會(huì)執(zhí)行def __init__方法，其關(guān)鍵執(zhí)行了self.RequestHandlerClass = RequestHandlerClass

class BaseServer:
    timeout = None

    def __init__(self, server_address, RequestHandlerClass):
        """Constructor.  May be extended, do not override."""
        self.server_address = server_address
        self.RequestHandlerClass = RequestHandlerClass
        self.__is_shut_down = threading.Event()
        self.__shutdown_request = False

    def finish_request(self, request, client_address):
        self.RequestHandlerClass(request, client_address, self)
        # self.RequestHandlerClass等同于self.WSGIRequestHandler

7.從self.RequestHandlerClass(request, client_address, self)，即去WSGIRequestHandler類里面初始化，根據(jù)一層層繼承關(guān)系，只要最老類BaseRequestHandler有初始化方法

class BaseRequestHandler:
    def __init__(self, request, client_address, server):
        self.request = request
        self.client_address = client_address
        self.server = server
        self.setup()
        try:
            self.handle()
        finally:
            self.finish()

從def __init__(self, request, client_address, server):進(jìn)入self.handle()
8.1 此時(shí)的self.handle()，根據(jù)繼承關(guān)系，其就在最小子類WSGIRequestHandler里面

    def handle(self):
        self.close_connection = True
        self.handle_one_request()
        while not self.close_connection:
            self.handle_one_request()
        try:
            self.connection.shutdown(socket.SHUT_WR)
        except (AttributeError, OSError):
            pass

9.從def handle(self)進(jìn)入self.handle_one_request()

    def handle_one_request(self):
        """Copy of WSGIRequestHandler.handle() but with different ServerHandler"""
        self.raw_requestline = self.rfile.readline(65537)
        if len(self.raw_requestline) > 65536:
            self.requestline = ''
            self.request_version = ''
            self.command = ''
            self.send_error(414)
            return

        if not self.parse_request():  # An error code has been sent, just exit
            return

        handler = ServerHandler(
            self.rfile, self.wfile, self.get_stderr(), self.get_environ()
        )
        handler.request_handler = self      # backpointer for logging & connection closing
        handler.run(self.server.get_app())

10.從def handle_one_request(self)進(jìn)入handler.run(self.server.get_app())
10.1 注意此時(shí)handler為ServerHandler實(shí)例化對(duì)象，run方法存在它的最大父類BaseHandler里面
10.2 此時(shí)handler.run(self.server.get_app())執(zhí)行了self.server.get_app()，其返回django.contrib.staticfiles.handlers.StaticFilesHandler，handler.run把其當(dāng)參數(shù)傳遞了過(guò)去

    def run(self, application):
        try:
            self.setup_environ()
            self.result = application(self.environ, self.start_response)
            self.finish_response()
        except (ConnectionAbortedError, BrokenPipeError, ConnectionResetError):

            return
        except:
			---

11.從def run(self, application)進(jìn)入self.result = application(self.environ, self.start_response)，其中application是django.contrib.staticfiles.handlers.StaticFilesHandler
11.1 其中self.application已經(jīng)初始化了是WSGIHandler

class StaticFilesHandler(StaticFilesHandlerMixin, WSGIHandler):
    def __init__(self, application):
        self.application = application
        self.base_url = urlparse(self.get_base_url())
        super().__init__()

    def __call__(self, environ, start_response):
        if not self._should_handle(get_path_info(environ)):
            return self.application(environ, start_response)
        return super().__call__(environ, start_response)

12.進(jìn)入后執(zhí)行def __call__(self, environ, start_response)方法，進(jìn)入return self.application(environ, start_response)，此時(shí)self.application已經(jīng)初始化了是WSGIHandler
12.1 request = self.request_class(environ)獲取到用戶請(qǐng)求的url后面就開(kāi)始配置runserver啟動(dòng)時(shí)候加載的url； response = self.get_response(request)獲取用戶url對(duì)應(yīng)的響應(yīng)準(zhǔn)備開(kāi)始往視圖轉(zhuǎn)

    def __call__(self, environ, start_response):
        set_script_prefix(get_script_name(environ))
        signals.request_started.send(sender=self.__class__, environ=environ)
        request = self.request_class(environ)
        response = self.get_response(request)
		---

13.進(jìn)入response = self.get_response(request)，結(jié)束，再下一步就要開(kāi)始中間件的進(jìn)行

    def get_response(self, request):
        set_urlconf(settings.ROOT_URLCONF)
        response = self._middleware_chain(request)
        response._resource_closers.append(request.close)
        if response.status_code >= 400:
            log_response(
                '%s: %s', response.reason_phrase, request.path,
                response=response,
                request=request,
            )
        return response

3.中間件的執(zhí)行

解釋：中間件的執(zhí)行需要聯(lián)系著上面運(yùn)行過(guò)程，這個(gè)過(guò)程是一個(gè)遞歸的過(guò)程，下面介紹的五個(gè)函數(shù)是中間件命名規(guī)則對(duì)應(yīng)得內(nèi)容

process_request()：完成請(qǐng)求對(duì)象的創(chuàng)建，但用戶訪問(wèn)的網(wǎng)址尚未與網(wǎng)站的路由地址匹配。
process_view()：完成用戶訪問(wèn)的網(wǎng)址與路由地址的匹配，但尚未執(zhí)行視圖函數(shù)。
process_exception()：在執(zhí)行視圖函數(shù)的期間發(fā)生異常，比如代碼異常，主動(dòng)拋出404異常等。
process_response()：完成視圖函數(shù)的執(zhí)行，但尚未將響應(yīng)內(nèi)容返回瀏覽器
process_template_response()：默認(rèn)不執(zhí)行，在視圖函數(shù)完成操作后調(diào)用，除非視圖函數(shù)返回的response中有render方法(幾乎不會(huì)用，可以忽略)

1.遞歸的進(jìn)入階段：循環(huán)進(jìn)行下面的代碼（此代碼位置django\core\handlers\exception.py）

1.1 此處出現(xiàn)process_request()和process_response()

        @wraps(get_response)
        def inner(request):
            try:
                response = get_response(request) # 此進(jìn)入循環(huán)
            except Exception as exc:
                response = response_for_exception(request, exc)
            return response
        return inner

    def __call__(self, request):
        # Exit out to async mode, if needed
        if asyncio.iscoroutinefunction(self.get_response):
            return self.__acall__(request)
        response = None
        if hasattr(self, 'process_request'):
            response = self.process_request(request) # 進(jìn)行中間件的process_request步驟
        response = response or self.get_response(request) # 此進(jìn)入循環(huán)
        if hasattr(self, 'process_response'):
            response = self.process_response(request, response) # 此是遞歸后執(zhí)行的
        return response

2.遞歸的結(jié)束準(zhǔn)備回傳：進(jìn)行下面的代碼（此代碼位置django\core\handlers\base.py）
2.1 此處出現(xiàn)process_view()、process_template_response()和process_exception()

進(jìn)入視圖的關(guān)鍵函數(shù)：

callback, callback_args, callback_kwargs = self.resolve_request(request) # callback即對(duì)于視圖函數(shù)url匹配到對(duì)應(yīng)的view函數(shù)
for middleware_method in self._view_middleware_view_middleware里面放著所有的process_view()函數(shù)（初始化時(shí)加載的）， process_view()正是在該代碼下面的環(huán)節(jié)循環(huán)執(zhí)行
response = wrapped_callback(request, *callback_args, **callback_kwargs) 回調(diào)函數(shù)傳參，并返回試圖函數(shù)響應(yīng)。
沿著這個(gè)路徑連續(xù)進(jìn)入兩次，就到了后面講到的as_view里面（此內(nèi)容是專門(mén)視圖處理的前的關(guān)鍵步驟）
response = self.process_exception_by_middleware(e, request)對(duì)應(yīng)process_exception()
self._template_response_middleware 循環(huán)加載模板中間件

 def _get_response(self, request):
        response = None
        callback, callback_args, callback_kwargs = self.resolve_request(request)
        for middleware_method in self._view_middleware:
            response = middleware_method(request, callback, callback_args, callback_kwargs)
            if response:
                break
        if response is None:
            wrapped_callback = self.make_view_atomic(callback) # 找到視圖函數(shù)
            # If it is an asynchronous view, run it in a subthread.
            if asyncio.iscoroutinefunction(wrapped_callback):
                wrapped_callback = async_to_sync(wrapped_callback)
            try:
                response = wrapped_callback(request, *callback_args, **callback_kwargs)
            except Exception as e:
                response = self.process_exception_by_middleware(e, request)
                if response is None:
                    raise
        self.check_response(response, callback)
        if hasattr(response, 'render') and callable(response.render):
            for middleware_method in self._template_response_middleware:
                response = middleware_method(request, response)
                self.check_response(
                    response,
                    middleware_method,
                    name='%s.process_template_response' % (
                        middleware_method.__self__.__class__.__name__,
                    )
                )
            try:
                response = response.render()
            except Exception as e:
                response = self.process_exception_by_middleware(e, request)
                if response is None:
                    raise
        return response

3.遞歸的結(jié)束回傳：循環(huán)進(jìn)行下面的代碼

        @wraps(get_response)
        def inner(request):
            try:
                response = get_response(request) # 此進(jìn)入循環(huán)
            except Exception as exc:
                response = response_for_exception(request, exc)
            return response
        return inner

    def __call__(self, request):
        # Exit out to async mode, if needed
        if asyncio.iscoroutinefunction(self.get_response):
            return self.__acall__(request)
        response = None
        if hasattr(self, 'process_request'):
            response = self.process_request(request) 
        response = response or self.get_response(request) # 此進(jìn)入循環(huán)
        if hasattr(self, 'process_response'):
            response = self.process_response(request, response) # 進(jìn)行中間件的process_response步驟
        return response

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