第二篇：白话tornado源码之待请求阶段
https://www.cnblogs.com/wupeiqi/p/4375610.html
上篇《白话tornado源码之一个脚本引发的血案》用上帝视角多整个框架做了一个概述，同时也看清了web框架的的本质，下面我们从tornado程序的起始来分析其源码。
概述
上图是tornado程序启动以及接收到客户端请求后的整个过程，对于整个过程可以分为两大部分：
- 启动程序阶段，又称为待请求阶段（上图1、2所有系列和3.0）
- 接收并处理客户端请求阶段（上图3系列）
简而言之：
1、在启动程序阶段，第一步，获取配置文件然后生成url映射（即：一个url对应一个XXRequestHandler，从而让XXRequestHandler来处理指定url发送的请求）；第二步，创建服务器socket对象并添加到epoll中；第三步，创建无线循环去监听epoll。
2、在接收并处理请求阶段，第一步，接收客户端socket发送的请求（socket.accept）；第二步，从请求中获取请求头信息，再然后根据请求头中的请求url去匹配某个XXRequestHandler；第三步，匹配成功的XXRequestHandler处理请求；第四步，将处理后的请求发送给客户端；第五步，关闭客户端socket。
本篇的内容主要剖析【启动程序阶段】，下面我们就来一步一步的剖析整个过程，在此阶段主要是有下面重点标注的三个方法来实现。
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, world")
application = tornado.web.Application([
(r"/index", MainHandler),
])
if __name__ == "__main__":
application.listen(8888)
tornado.ioloop.IOLoop.instance().start()
一、application = tornado.web.Application([(xxx,xxx)])
执行Application类的构造函数，并传入一个列表类型的参数，这个列表里保存的是url规则和对应的处理类，即：当客户端的请求url可以配置这个规则时，那么该请求就交由对应的Handler去执行。
注意：Handler泛指继承自RequestHandler的所有类
Handlers泛指继承自RequestHandler的所有类的集合
class Application(object):
def __init__(self, handlers=None, default_host="", transforms=None,wsgi=False, **settings):
#设置响应的编码和返回方式，对应的http相应头：Content-Encoding和Transfer-Encoding
#Content-Encoding:gzip 表示对数据进行压缩，然后再返回给用户，从而减少流量的传输。
#Transfer-Encoding:chunck 表示数据的传送方式通过一块一块的传输。
if transforms is None:
self.transforms = []
if settings.get("gzip"):
self.transforms.append(GZipContentEncoding)
self.transforms.append(ChunkedTransferEncoding)
else:
self.transforms = transforms
#将参数赋值为类的变量
self.handlers = []
self.named_handlers = {}
self.default_host = default_host
self.settings = settings
#ui_modules和ui_methods用于在模版语言中扩展自定义输出
#这里将tornado内置的ui_modules和ui_methods添加到类的成员变量self.ui_modules和self.ui_methods中
self.ui_modules = {'linkify': _linkify,
'xsrf_form_html': _xsrf_form_html,
'Template': TemplateModule,
}
self.ui_methods = {}
self._wsgi = wsgi
#获取获取用户自定义的ui_modules和ui_methods，并将他们添加到之前创建的成员变量self.ui_modules和self.ui_methods中
self._load_ui_modules(settings.get("ui_modules", {}))
self._load_ui_methods(settings.get("ui_methods", {}))
#设置静态文件路径，设置方式则是通过正则表达式匹配url，让StaticFileHandler来处理匹配的url
if self.settings.get("static_path"):
#从settings中读取key为static_path的值，用于设置静态文件路径
path = self.settings["static_path"]
#获取参数中传入的handlers，如果空则设置为空列表
handlers = list(handlers or [])
#静态文件前缀，默认是/static/
static_url_prefix = settings.get("static_url_prefix","/static/")
#在参数中传入的handlers前再添加三个映射：
#【/static/.*】 --> StaticFileHandler
#【/(favicon\.ico)】 --> StaticFileHandler
#【/(robots\.txt)】 --> StaticFileHandler
handlers = [
(re.escape(static_url_prefix) + r"(.*)", StaticFileHandler,dict(path=path)),
(r"/(favicon\.ico)", StaticFileHandler, dict(path=path)),
(r"/(robots\.txt)", StaticFileHandler, dict(path=path)),
] + handlers
#执行本类的Application的add_handlers方法
#此时，handlers是一个列表，其中的每个元素都是一个对应关系，即：url正则表达式和处理匹配该正则的url的Handler
if handlers: self.add_handlers(".*$", handlers)
# Automatically reload modified modules
#如果settings中设置了 debug 模式，那么就使用自动加载重启
if self.settings.get("debug") and not wsgi:
import autoreload
autoreload.start()
class Application(object):
def add_handlers(self, host_pattern, host_handlers):
#如果主机模型最后没有结尾符，那么就为他添加一个结尾符。
if not host_pattern.endswith("$"):
host_pattern += "$"
handlers = []
#对主机名先做一层路由映射，例如：http://www.wupeiqi.com 和 http://safe.wupeiqi.com
#即：safe对应一组url映射，www对应一组url映射，那么当请求到来时，先根据它做第一层匹配，之后再继续进入内部匹配。
#对于第一层url映射来说，由于.*会匹配所有的url，所将 .* 的永远放在handlers列表的最后，不然 .* 就会截和了...
#re.complie是编译正则表达式，以后请求来的时候只需要执行编译结果的match方法就可以去匹配了
if self.handlers and self.handlers[-1][0].pattern == '.*$':
self.handlers.insert(-1, (re.compile(host_pattern), handlers))
else:
self.handlers.append((re.compile(host_pattern), handlers))
#遍历我们设置的和构造函数中添加的【url->Handler】映射，将url和对应的Handler封装到URLSpec类中(构造函数中会对url进行编译)
#并将所有的URLSpec对象添加到handlers列表中，而handlers列表和主机名模型组成一个元祖，添加到self.Handlers列表中。
for spec in host_handlers:
if type(spec) is type(()):
assert len(spec) in (2, 3)
pattern = spec[0]
handler = spec[1]
if len(spec) == 3:
kwargs = spec[2]
else:
kwargs = {}
spec = URLSpec(pattern, handler, kwargs)
handlers.append(spec)
if spec.name:
#未使用该功能，默认spec.name = None
if spec.name in self.named_handlers:
logging.warning("Multiple handlers named %s; replacing previous value",spec.name)
self.named_handlers[spec.name] = spec
class URLSpec(object):
def __init__(self, pattern, handler_class, kwargs={}, name=None):
if not pattern.endswith('$'):
pattern += '$'
self.regex = re.compile(pattern)
self.handler_class = handler_class
self.kwargs = kwargs
self.name = name
self._path, self._group_count = self._find_groups()
上述代码主要完成了以下功能：加载配置信息和生成url映射，并且把所有的信息封装在一个application对象中。
加载的配置信息包括：
- 编码和返回方式信息
- 静态文件路径
- ui_modules（模版语言中使用，暂时忽略）
- ui_methods（模版语言中使用，暂时忽略）
- 是否debug模式运行
以上的所有配置信息，都可以在settings中配置，然后在创建Application对象时候，传入参数即可。如：application = tornado.web.Application([(r"/index", MainHandler),],**settings)
生成url映射：
- 将url和对应的Handler添加到对应的主机前缀中，如：safe.index.com、www.auto.com
封装数据：
将配置信息和url映射关系封装到Application对象中，信息分别保存在Application对象的以下字段中：
- self.transforms，保存着编码和返回方式信息
- self.settings，保存着配置信息
- self.ui_modules，保存着ui_modules信息
- self.ui_methods，保存这ui_methods信息
- self.handlers，保存着所有的主机名对应的Handlers，每个handlers则是url正则对应的Handler
二、application.listen(xxx)
第一步操作将配置和url映射等信息封装到了application对象中，而这第二步执行application对象的listen方法，该方法内部又把之前包含各种信息的application对象封装到了一个HttpServer对象中，然后继续调用HttpServer对象的liseten方法。
class Application(object):
#创建服务端socket，并绑定IP和端口并添加相应设置，注：未开始通过while监听accept，等待客户端连接
def listen(self, port, address="", **kwargs):
from tornado.httpserver import HTTPServer
server = HTTPServer(self, **kwargs)
server.listen(port, address)
详细代码：
class HTTPServer(object):
def __init__(self, request_callback, no_keep_alive=False, io_loop=None,xheaders=False, ssl_options=None):
#Application对象
self.request_callback = request_callback
#是否长连接
self.no_keep_alive = no_keep_alive
#IO循环
self.io_loop = io_loop
self.xheaders = xheaders
#Http和Http
self.ssl_options = ssl_options
self._socket = None
self._started = False
def listen(self, port, address=""):
self.bind(port, address)
self.start(1)
def bind(self, port, address=None, family=socket.AF_UNSPEC):
assert not self._socket
#创建服务端socket对象，IPV4和TCP连接
self._socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
flags = fcntl.fcntl(self._socket.fileno(), fcntl.F_GETFD)
flags |= fcntl.FD_CLOEXEC
fcntl.fcntl(self._socket.fileno(), fcntl.F_SETFD, flags)
#配置socket对象
self._socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
self._socket.setblocking(0)
#绑定IP和端口
self._socket.bind((address, port))
#最大阻塞数量
self._socket.listen(128)
def start(self, num_processes=1):
assert not self._started
self._started = True
if num_processes is None or num_processes <= 0:
num_processes = _cpu_count()
if num_processes > 1 and ioloop.IOLoop.initialized():
logging.error("Cannot run in multiple processes: IOLoop instance "
"has already been initialized. You cannot call "
"IOLoop.instance() before calling start()")
num_processes = 1
#如果进程数大于1
if num_processes > 1:
logging.info("Pre-forking %d server processes", num_processes)
for i in range(num_processes):
if os.fork() == 0:
import random
from binascii import hexlify
try:
# If available, use the same method as
# random.py
seed = long(hexlify(os.urandom(16)), 16)
except NotImplementedError:
# Include the pid to avoid initializing two
# processes to the same value
seed(int(time.time() * 1000) ^ os.getpid())
random.seed(seed)
self.io_loop = ioloop.IOLoop.instance()
self.io_loop.add_handler(
self._socket.fileno(), self._handle_events,
ioloop.IOLoop.READ)
return
os.waitpid(-1, 0)
#进程数等于1，默认
else:
if not self.io_loop:
#设置成员变量self.io_loop为IOLoop的实例，注：IOLoop使用methodclass完成了一个单例模式
self.io_loop = ioloop.IOLoop.instance()
#执行IOLoop的add_handler方法，将socket句柄、self._handle_events方法和IOLoop.READ当参数传入
self.io_loop.add_handler(self._socket.fileno(),
self._handle_events,
ioloop.IOLoop.READ)
def _handle_events(self, fd, events):
while True:
try:
#====important=====#
connection, address = self._socket.accept()
except socket.error, e:
if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
return
raise
if self.ssl_options is not None:
assert ssl, "Python 2.6+ and OpenSSL required for SSL"
try:
#====important=====#
connection = ssl.wrap_socket(connection,server_side=True,do_handshake_on_connect=False,**self.ssl_options)
except ssl.SSLError, err:
if err.args[0] == ssl.SSL_ERROR_EOF:
return connection.close()
else:
raise
except socket.error, err:
if err.args[0] == errno.ECONNABORTED:
return connection.close()
else:
raise
try:
if self.ssl_options is not None:
stream = iostream.SSLIOStream(connection, io_loop=self.io_loop)
else:
stream = iostream.IOStream(connection, io_loop=self.io_loop)
#====important=====#
HTTPConnection(stream, address, self.request_callback,self.no_keep_alive, self.xheaders)
except:
logging.error("Error in connection callback", exc_info=True)
class IOLoop(object):
# Constants from the epoll module
_EPOLLIN = 0x001
_EPOLLPRI = 0x002
_EPOLLOUT = 0x004
_EPOLLERR = 0x008
_EPOLLHUP = 0x010
_EPOLLRDHUP = 0x2000
_EPOLLONESHOT = (1 << 30)
_EPOLLET = (1 << 31)
# Our events map exactly to the epoll events
NONE = 0
READ = _EPOLLIN
WRITE = _EPOLLOUT
ERROR = _EPOLLERR | _EPOLLHUP | _EPOLLRDHUP
def __init__(self, impl=None):
self._impl = impl or _poll()
if hasattr(self._impl, 'fileno'):
self._set_close_exec(self._impl.fileno())
self._handlers = {}
self._events = {}
self._callbacks = []
self._timeouts = []
self._running = False
self._stopped = False
self._blocking_signal_threshold = None
# Create a pipe that we send bogus data to when we want to wake
# the I/O loop when it is idle
if os.name != 'nt':
r, w = os.pipe()
self._set_nonblocking(r)
self._set_nonblocking(w)
self._set_close_exec(r)
self._set_close_exec(w)
self._waker_reader = os.fdopen(r, "rb", 0)
self._waker_writer = os.fdopen(w, "wb", 0)
else:
self._waker_reader = self._waker_writer = win32_support.Pipe()
r = self._waker_writer.reader_fd
self.add_handler(r, self._read_waker, self.READ)
@classmethod
def instance(cls):
if not hasattr(cls, "_instance"):
cls._instance = cls()
return cls._instance
def add_handler(self, fd, handler, events):
"""Registers the given handler to receive the given events for fd."""
self._handlers[fd] = stack_context.wrap(handler)
self._impl.register(fd, events | self.ERROR)
def wrap(fn):
'''Returns a callable object that will resore the current StackContext
when executed.
Use this whenever saving a callback to be executed later in a
different execution context (either in a different thread or
asynchronously in the same thread).
'''
if fn is None:
return None
# functools.wraps doesn't appear to work on functools.partial objects
#@functools.wraps(fn)
def wrapped(callback, contexts, *args, **kwargs):
# If we're moving down the stack, _state.contexts is a prefix
# of contexts. For each element of contexts not in that prefix,
# create a new StackContext object.
# If we're moving up the stack (or to an entirely different stack),
# _state.contexts will have elements not in contexts. Use
# NullContext to clear the state and then recreate from contexts.
if (len(_state.contexts) > len(contexts) or
any(a[1] is not b[1]
for a, b in itertools.izip(_state.contexts, contexts))):
# contexts have been removed or changed, so start over
new_contexts = ([NullContext()] +
[cls(arg) for (cls,arg) in contexts])
else:
new_contexts = [cls(arg)
for (cls, arg) in contexts[len(_state.contexts):]]
if len(new_contexts) > 1:
with contextlib.nested(*new_contexts):
callback(*args, **kwargs)
elif new_contexts:
with new_contexts[0]:
callback(*args, **kwargs)
else:
callback(*args, **kwargs)
if getattr(fn, 'stack_context_wrapped', False):
return fn
contexts = _state.contexts
result = functools.partial(wrapped, fn, contexts)
result.stack_context_wrapped = True
return result
备注：stack_context.wrap其实就是对函数进行一下封装，即：函数在不同情况下上下文信息可能不同。
上述代码本质上就干了以下这么四件事：
- 把包含了各种配置信息的application对象封装到了HttpServer对象的request_callback字段中
- 创建了服务端socket对象
- 单例模式创建IOLoop对象，然后将socket对象句柄作为key，被封装了的函数_handle_events作为value，添加到IOLoop对象的_handlers字段中
- 向epoll中注册监听服务端socket对象的读可用事件
目前，我们只是看到上述代码大致干了这四件事，而其目的有什么？他们之间的联系又是什么呢？
答：现在不妨先来做一个猜想，待之后再在源码中确认验证是否正确！猜想：通过epoll监听服务端socket事件，一旦请求到达时，则执行3中被封装了的_handle_events函数，该函数又利用application中封装了的各种配置信息对客户端url来指定判定，然后指定对应的Handler处理该请求。
注意：使用epoll创建服务端socket
import socket, select
EOL1 = b'/n/n'
EOL2 = b'/n/r/n'
response = b'HTTP/1.0 200 OK/r/nDate: Mon, 1 Jan 1996 01:01:01 GMT/r/n'
response += b'Content-Type: text/plain/r/nContent-Length: 13/r/n/r/n'
response += b'Hello, world!'
serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
serversocket.bind(('0.0.0.0', 8080))
serversocket.listen(1)
serversocket.setblocking(0)
epoll = select.epoll()
epoll.register(serversocket.fileno(), select.EPOLLIN)
try:
connections = {}; requests = {}; responses = {}
while True:
events = epoll.poll(1)
for fileno, event in events:
if fileno == serversocket.fileno():
connection, address = serversocket.accept()
connection.setblocking(0)
epoll.register(connection.fileno(), select.EPOLLIN)
connections[connection.fileno()] = connection
requests[connection.fileno()] = b''
responses[connection.fileno()] = response
elif event & select.EPOLLIN:
requests[fileno] += connections[fileno].recv(1024)
if EOL1 in requests[fileno] or EOL2 in requests[fileno]:
epoll.modify(fileno, select.EPOLLOUT)
print('-'*40 + '/n' + requests[fileno].decode()[:-2])
elif event & select.EPOLLOUT:
byteswritten = connections[fileno].send(responses[fileno])
responses[fileno] = responses[fileno][byteswritten:]
if len(responses[fileno]) == 0:
epoll.modify(fileno, 0)
connections[fileno].shutdown(socket.SHUT_RDWR)
elif event & select.EPOLLHUP:
epoll.unregister(fileno)
connections[fileno].close()
del connections[fileno]
finally:
epoll.unregister(serversocket.fileno())
epoll.close()
serversocket.close()
上述，其实就是利用epoll对象的poll(timeout)方法去轮询已经注册在epoll中的socket句柄，当有读可用的信息时候，则返回包含当前句柄和Event Code的序列，然后在通过句柄对客户端的请求进行处理
三、tornado.ioloop.IOLoop.instance().start()
上一步中创建了socket对象并使得socket对象和epoll建立了关系，该步骤则就来执行epoll的epoll方法去轮询已经注册在epoll对象中的socket句柄，当有读可用信息时，则触发一些操作什么的....
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class IOLoop(object): def add_handler(self, fd, handler, events): #HttpServer的Start方法中会调用该方法 self._handlers[fd] = stack_context.wrap(handler) self._impl.register(fd, events | self.ERROR) def start(self): while True: poll_timeout = 0.2 try: #epoll中轮询 event_pairs = self._impl.poll(poll_timeout) except Exception, e: #省略其他 #如果有读可用信息，则把该socket对象句柄和Event Code序列添加到self._events中 self._events.update(event_pairs) #遍历self._events，处理每个请求 while self._events: fd, events = self._events.popitem() try: #以socket为句柄为key，取出self._handlers中的stack_context.wrap(handler)，并执行 #stack_context.wrap(handler)包装了HTTPServer类的_handle_events函数的一个函数 #是在上一步中执行add_handler方法时候，添加到self._handlers中的数据。 self._handlers[fd](fd, events) except: #省略其他 |
class IOLoop(object):
def start(self):
"""Starts the I/O loop.
The loop will run until one of the I/O handlers calls stop(), which
will make the loop stop after the current event iteration completes.
"""
if self._stopped:
self._stopped = False
return
self._running = True
while True:
# Never use an infinite timeout here - it can stall epoll
poll_timeout = 0.2
# Prevent IO event starvation by delaying new callbacks
# to the next iteration of the event loop.
callbacks = self._callbacks
self._callbacks = []
for callback in callbacks:
self._run_callback(callback)
if self._callbacks:
poll_timeout = 0.0
if self._timeouts:
now = time.time()
while self._timeouts and self._timeouts[0].deadline <= now:
timeout = self._timeouts.pop(0)
self._run_callback(timeout.callback)
if self._timeouts:
milliseconds = self._timeouts[0].deadline - now
poll_timeout = min(milliseconds, poll_timeout)
if not self._running:
break
if self._blocking_signal_threshold is not None:
# clear alarm so it doesn't fire while poll is waiting for
# events.
signal.setitimer(signal.ITIMER_REAL, 0, 0)
try:
event_pairs = self._impl.poll(poll_timeout)
except Exception, e:
# Depending on python version and IOLoop implementation,
# different exception types may be thrown and there are
# two ways EINTR might be signaled:
# * e.errno == errno.EINTR
# * e.args is like (errno.EINTR, 'Interrupted system call')
if (getattr(e, 'errno', None) == errno.EINTR or
(isinstance(getattr(e, 'args', None), tuple) and
len(e.args) == 2 and e.args[0] == errno.EINTR)):
continue
else:
raise
if self._blocking_signal_threshold is not None:
signal.setitimer(signal.ITIMER_REAL,
self._blocking_signal_threshold, 0)
# Pop one fd at a time from the set of pending fds and run
# its handler. Since that handler may perform actions on
# other file descriptors, there may be reentrant calls to
# this IOLoop that update self._events
self._events.update(event_pairs)
while self._events:
fd, events = self._events.popitem()
try:
self._handlers[fd](fd, events)
except (KeyboardInterrupt, SystemExit):
raise
except (OSError, IOError), e:
if e.args[0] == errno.EPIPE:
# Happens when the client closes the connection
pass
else:
logging.error("Exception in I/O handler for fd %d",
fd, exc_info=True)
except:
logging.error("Exception in I/O handler for fd %d",
fd, exc_info=True)
# reset the stopped flag so another start/stop pair can be issued
self._stopped = False
if self._blocking_signal_threshold is not None:
signal.setitimer(signal.ITIMER_REAL, 0, 0)
对于上述代码，执行start方法后，程序就进入“死循环”，也就是会一直不停的轮询的去检查是否有请求到来，如果有请求到达，则执行封装了HttpServer类的_handle_events方法和相关上下文的stack_context.wrap(handler)（其实就是执行HttpServer类的_handle_events方法），详细见下篇博文，简要代码如下：
class HTTPServer(object):
def _handle_events(self, fd, events):
while True:
try:
connection, address = self._socket.accept()
except socket.error, e:
if e.args[0] in (errno.EWOULDBLOCK, errno.EAGAIN):
return
raise
if self.ssl_options is not None:
assert ssl, "Python 2.6+ and OpenSSL required for SSL"
try:
connection = ssl.wrap_socket(connection,
server_side=True,
do_handshake_on_connect=False,
**self.ssl_options)
except ssl.SSLError, err:
if err.args[0] == ssl.SSL_ERROR_EOF:
return connection.close()
else:
raise
except socket.error, err:
if err.args[0] == errno.ECONNABORTED:
return connection.close()
else:
raise
try:
if self.ssl_options is not None:
stream = iostream.SSLIOStream(connection, io_loop=self.io_loop)
else:
stream = iostream.IOStream(connection, io_loop=self.io_loop)
HTTPConnection(stream, address, self.request_callback,
self.no_keep_alive, self.xheaders)
except:
logging.error("Error in connection callback", exc_info=True)
结束
本篇博文介绍了“待请求阶段”的所作所为，简要来说其实就是三件事：其一、把setting中的各种配置以及url和Handler之间的映射关系封装到来application对象中（application对象又被封装到了HttpServer对象的request_callback字段中）；其二、结合epoll创建服务端socket；其三、当请求到达时交由HttpServer类的_handle_events方法处理请求，即：处理请求的入口。对于处理请求的详细，请参见下篇博客（客官莫急，加班编写中...）
