Django源码分析(一)--runserver启动过程分析

Django框架总览

Django运行方式

一般运行 Django 项目的方法有两种:

• 在开发和调试中一般用 runserver 方法, 使用 Django 自己的 Web Server

• 正式生产环境一般用 uWSGI、fastcgi 等协议运行 Django 项目

1、runserver 方式

用法：(./manage.py help runserver查看)

usage: manage.py runserver [-h] [--version] [-v {0,1,2,3}]
                           [--settings SETTINGS] [--pythonpath PYTHONPATH]
                           [--traceback] [--no-color] [--ipv6] [--nothreading]
                           [--noreload] [--nostatic] [--insecure]
                           [addrport]

python manage.py runserver # default port is 8000
python manage.py runserver 8080 
python manage.py runserver 127.0.0.1:8000

查看 manage.py 内容可以发现, 首先

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "fadada.settings")

设置了一个环境变量 DJANGO_SETTINGS_MODULE 等于 project.settings, 然后直接执行 django.core.management 中的 execute_from_command_line 方法, 并把命令行输入的参数传进去。

一路看到 ManagementUtility 的 execute 方法:

#django\core\management\__init__.py
class ManagementUtility:
    def execute(self):
        """
        Given the command-line arguments, figure out which subcommand is being
        run, create a parser appropriate to that command, and run it.
        """
        ...
        self.autocomplete()
        ...
        self.fetch_command(subcommand).run_from_argv(self.argv)

# django\core\management\base.py
class BaseCommand:
    def run_from_argv(self, argv):
        ...
        self.execute(*args, **cmd_options)
        ...

# django\core\management\commands\runserver.py
class Command(BaseCommand):
    def execute(self, *args, **options):
        if options['no_color']:
            # We rely on the environment because it's currently the only
            # way to reach WSGIRequestHandler. This seems an acceptable
            # compromise considering `runserver` runs indefinitely.
            os.environ["DJANGO_COLORS"] = "nocolor"
        super().execute(*args, **options)

# django\core\management\base.py
class BaseCommand:
    def execute(self, *args, **options):
        ...
        output = self.handle(*args, **options)
        ...

# django\contrib\staticfiles\management\commands\runserver.py
class Command(BaseCommand):
    def get_handler(self, *args, **options):
        """Return the default WSGI handler for the runner."""
        return get_internal_wsgi_application()
    def handle(self, *args, **options):
        ...
        self.run(**options)
        ...

    def run(self, **options):
        ...
        self.inner_run(None, **options)

    def inner_run(self, *args, **options):
        ...
            handler = self.get_handler(*args, **options)
            run(self.addr, int(self.port), handler,
                ipv6=self.use_ipv6, threading=threading, server_cls=self.server_cls)

# django\core\servers\basehttp.py
def get_internal_wsgi_application():
    ...
    return get_wsgi_application()

class WSGIRequestHandler(simple_server.WSGIRequestHandler):

def run(addr, port, wsgi_handler, ipv6=False, threading=False, server_cls=WSGIServer):
    ...
    httpd.set_app(wsgi_handler)     # 这里的wsgi_hander 是get_handler返回的一个 WSGIHandler 对象
    httpd.serve_forever()

# django\core\wsgi.py
def get_wsgi_application():
    django.setup(set_prefix=False)
    return WSGIHandler()

# django\core\handlers\wsgi.py
class WSGIHandler(base.BaseHandler):
    request_class = WSGIRequest

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.load_middleware()

# django\core\handlers\base.py
class BaseHandler:
    ...

runserver 命令先解析参数, 后面通过 django.core.servers.basehttp.get_internal_wsgi_application 方法获取 wsgi_handler, 这个方法先根据 settings 中的 WSGI_APPLICATION 来获取 handler, 在创建 project 的时候， Django 会默认创建一个 wsgi.py 文件，而 settings 中的 WSGI_APPLICATION 配置也会默认指向这个文件。看一下这个 wsgi.py 文件，其实它也和上面的逻辑一样，最终调用 get_wsgi_application 实现。

然后根据 ip address 和 port 生成一个 WSGIServer 对象 httpd，接受用户请求。

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:
        # ThreadingMixIn.daemon_threads indicates how threads will behave on an
        # abrupt shutdown; like quitting the server by the user or restarting
        # by the auto-reloader. True means the server will not wait for thread
        # termination before it quits. This will make auto-reloader faster
        # and will prevent the need to kill the server manually if a thread
        # isn't terminating correctly.
        httpd.daemon_threads = True
    httpd.set_app(wsgi_handler)
    httpd.serve_forever()

WSGIHandler 会初始化中间件并加载 settings.MIDDLEWARE 中的中间件, 关于中间件的问题下节再讲~