##前言 本文将尝试详细的带大家一步步走完一个异步操作,从而了解tornado是如何实现异步io的. 其实本文是对上一篇文的实践和复习 主旨在于关注异步io的实现,所以会忽略掉代码中的一些异常处理.文字较多,凑合下吧
接下来只会贴出部分源码,帮助理解,希望有耐心的同学打开tornado源码,一起跟踪一遍吧.
AsyncHTTPClient :
AsyncHTTPClient 继承 Configurable ,从__new__重看出是单例模式.
根据 Configurable 的__new__和 AsyncHTTPClient 的 configurable_base 和 configurable_default 得知,
实例化后一定是 SimpleAsyncHTTPClient 的实例
fetch
def fetch(self, request, callback=None, raise_error=True, **kwargs):
if self._closed:
raise RuntimeError("fetch() called on closed AsyncHTTPClient")
if not isinstance(request, HTTPRequest):
request = HTTPRequest(url=request, **kwargs)
# We may modify this (to add Host, Accept-Encoding, etc),
# so make sure we don't modify the caller's object. This is also
# where normal dicts get converted to HTTPHeaders objects.
request.headers = httputil.HTTPHeaders(request.headers)
request = _RequestProxy(request, self.defaults)
future = TracebackFuture()
if callback is not None:
callback = stack_context.wrap(callback)
def handle_future(future):
exc = future.exception()
if isinstance(exc, HTTPError) and exc.response is not None:
response = exc.response
elif exc is not None:
response = HTTPResponse(
request, 599, error=exc,
request_time=time.time() - request.start_time)
else:
response = future.result()
self.io_loop.add_callback(callback, response)
future.add_done_callback(handle_future)
##fetch_impl带上handle_response,重点
def handle_response(response):
if raise_error and response.error:
future.set_exception(response.error)
else:
future.set_result(response)
self.fetch_impl(request, handle_response)
return future
fetch 中调用 fetch_impl,fetch_impl 中其中一个参数是 callback ,而代码中的 callback 包含了 future 的 set_result ,
所以,当 callback 被调用时,外部的 yield 操作将被激活,程序会在 ioloop 中调用此 callback ,然后回到原函数的 yield 处,
并且原函数返回此次 qeust 的 future 对象,以便在函数外部增加别的 callback
fetch_impl
def _connection_class(self):
return _HTTPConnection
def _handle_request(self, request, release_callback, final_callback):
self._connection_class()(
self.io_loop, self, request, release_callback,
final_callback, self.max_buffer_size, self.tcp_client,
self.max_header_size, self.max_body_size)
在 return 之前,继续查看 fetch_impl 内部是如何处理,根据推测,他一定是将继续处理网络请求,
肯定会将网络请求交由 ioloop 的 epoll 部分处理,设定好处理的 hanlder 再返回
future.set_result ,接下来继续分析 fetch_impl 内部是如果设置网络请求的.
fetch_impl 的实现代码中查看,实例化中创建了 tcpclient 对象,这个肯定是关键
根据之前的分析 SimpleAsyncHTTPClient 是单例模式,那他怎么处理各种 http 请求呢?
查看代码得知,他将请求的 request 和 callback 存储在 self.queue 中,
每次 fetch_impl 的时候,一个个 pop 出来处理就好了,这样就能处理n个请求了
一步步跟踪到 _handle_request ,发现最后到了 _HTTPConnection 的实例化中了.
实例化的参数有之前那个包含 future 的 callback .
这样就可以保证 yield 操作可以回到原处了.好了,继续走
_HTTPConnection
class _HTTPConnection(httputil.HTTPMessageDelegate):
_SUPPORTED_METHODS = set(["GET", "HEAD", "POST", "PUT", "DELETE", "PATCH", "OPTIONS"])
def __init__(self, io_loop, client, request, release_callback,
final_callback, max_buffer_size, tcp_client,
max_header_size, max_body_size):
self.start_time = io_loop.time()
self.io_loop = io_loop
self.client = client
self.request = request
self.release_callback = release_callback
self.final_callback = final_callback
self.max_buffer_size = max_buffer_size
self.tcp_client = tcp_client
self.max_header_size = max_header_size
self.max_body_size = max_body_size
self.code = None
self.headers = None
self.chunks = []
self._decompressor = None
# Timeout handle returned by IOLoop.add_timeout
self._timeout = None
self._sockaddr = None
with stack_context.ExceptionStackContext(self._handle_exception):
self.parsed = urlparse.urlsplit(_unicode(self.request.url))
if self.parsed.scheme not in ("http", "https"):
raise ValueError("Unsupported url scheme: %s" %
self.request.url)
# urlsplit results have hostname and port results, but they
# didn't support ipv6 literals until python 2.7.
netloc = self.parsed.netloc
if "@" in netloc:
userpass, _, netloc = netloc.rpartition("@")
host, port = httputil.split_host_and_port(netloc)
if port is None:
port = 443 if self.parsed.scheme == "https" else 80
if re.match(r'^\[.*\]$', host):
# raw ipv6 addresses in urls are enclosed in brackets
host = host[1:-1]
self.parsed_hostname = host # save final host for _on_connect
if request.allow_ipv6 is False:
af = socket.AF_INET
else:
af = socket.AF_UNSPEC
ssl_options = self._get_ssl_options(self.parsed.scheme)
timeout = min(self.request.connect_timeout, self.request.request_timeout)
if timeout:
self._timeout = self.io_loop.add_timeout(
self.start_time + timeout,
stack_context.wrap(self._on_timeout))
self.tcp_client.connect(host, port, af=af,
ssl_options=ssl_options,
max_buffer_size=self.max_buffer_size,
callback=self._on_connect)
_HTTPConnection 的实例化中有一堆成员变量,有点晕,
先不管这么多,关注我们的 callback ,和 tcpclient .
一行行往下看,是 host 和 port 的初始化操作 ,http 和 https 是不一样的嘛,当然得处理一下,
终于到了最后,是 tcpclient.connect ,从 connect 的参数中看到 callback=self._on_connect ,
应该是个重要的方法,出去那些字符串处理,发现 self.connection.write_headers(start_line , self.request.headers ) ,
这应该是发送 http 头的操作吧,是网络请求,所以这是处理 connect 这个 url 后,发送 http 头的操作.
还是回头看看是如何 connect 的吧,因为这是异步的关键,搞懂了这个,那剩下来的也是同出一则
TCPClient
转到 tcpclient 的代码去看他的实例化和 connect 操作,看来剩下的路还很长呢
TCPClient 实例化的代码很短,有个 resolver 对象,先不管
connect
@gen.coroutine
def connect(self, host, port, af=socket.AF_UNSPEC, ssl_options=None,
max_buffer_size=None):
"""Connect to the given host and port.
Asynchronously returns an `.IOStream` (or `.SSLIOStream` if
``ssl_options`` is not None).
"""
addrinfo = yield self.resolver.resolve(host, port, af)
connector = _Connector(
addrinfo, self.io_loop,
functools.partial(self._create_stream, max_buffer_size))
af, addr, stream = yield connector.start()
# TODO: For better performance we could cache the (af, addr)
# information here and re-use it on subsequent connections to
# the same host. (http://tools.ietf.org/html/rfc6555#section-4.2)
if ssl_options is not None:
stream = yield stream.start_tls(False, ssl_options=ssl_options,
server_hostname=host)
raise gen.Return(stream)
去到 connect 方法里,发现 coroutine 装饰器,并且调用时设置了 callback=self._on_connect ,
所以当这个 coroutine 的 future 被解决时,会调用 self._on_connect ,
你也可以看到 _on_connect 的参数是 stream ,就是 gen.Return(stream )传过去的.
因为 gen.coroutine 实现时的代码中,
send 了 value 后,代码继续走,走到 gen.Return (其实这是个 exception ,
就会走到 gen.coroutine 里的 set_result 了.)
第一个 yield 右边是 self.resolver.resolve ,左边是 addrinfo ,是地址信息,
这个异步操作处理的便是解析 url 的地址信息.此处 tornado 默认使用了阻塞的实现,暂时先不看,
以后在新的篇幅补充,主要内容是 run_on_executor 装饰器的内容,
此处其实是同步返回的,因为默认用的是 BlockingResolver 的代码,直接看下一个 yield
_Connector
def __init__(self, addrinfo, io_loop, connect):
self.io_loop = io_loop
self.connect = connect
self.future = Future()
self.timeout = None
self.last_error = None
self.remaining = len(addrinfo)
self.primary_addrs, self.secondary_addrs = self.split(addrinfo)
_Connector 实例化,参数有一个 callback ,是本类的 _create_stream ,
并把 self.connect 设置成传过来的 callback
所以 self.connect 就是 TCPClient._create_stream 了,
成员变量有个 future 实例,我们需要全程高度关注 future 和 callback .
实例化后调用了 start 方法 ,start 内部,调用 try_connect,set_timout ,
根据函数名得知,是 connect 操作和设置超时的操作.最后返回实例化时创建的 future .
try_connect
def start(self, timeout=_INITIAL_CONNECT_TIMEOUT):
self.try_connect(iter(self.primary_addrs))
self.set_timout(timeout)
return self.future
def try_connect(self, addrs):
try:
af, addr = next(addrs)
except StopIteration:
# We've reached the end of our queue, but the other queue
# might still be working. Send a final error on the future
# only when both queues are finished.
if self.remaining == 0 and not self.future.done():
self.future.set_exception(self.last_error or
IOError("connection failed"))
return
future = self.connect(af, addr)
future.add_done_callback(functools.partial(self.on_connect_done,
addrs, af, addr))
future = self.connect(af , addr ),执行了 TCPClient._create_stream 方法,
返回 future ,并且设置 future 的 callback=on_connect_done
_create_stream
def _create_stream(self, max_buffer_size, af, addr):
# Always connect in plaintext; we'll convert to ssl if necessary
# after one connection has completed.
stream = IOStream(socket.socket(af),
io_loop=self.io_loop,
max_buffer_size=max_buffer_size)
return stream.connect(addr)
实例化 IOStream ,执行并返回 stream.connect,stream.connect 返回的 future 便是 try_connect 中的 future ,
所以,进去看看 stream.connect 内部是怎么”解决”这个 future 的.
IOStream
connect
def connect(self, address, callback=None, server_hostname=None):
self._connecting = True
if callback is not None:
self._connect_callback = stack_context.wrap(callback)
future = None
else:
future = self._connect_future = TracebackFuture()
try:
self.socket.connect(address)
except socket.error as e:
if (errno_from_exception(e) not in _ERRNO_INPROGRESS and
errno_from_exception(e) not in _ERRNO_WOULDBLOCK):
if future is None:
gen_log.warning("Connect error on fd %s: %s",
self.socket.fileno(), e)
self.close(exc_info=True)
return future
self._add_io_state(self.io_loop.WRITE)
return future
self._connecting = True 设置此实例正在连接中,连接完毕设置成 false
如果没有 callback 传入,生成 future 对象, 刚才返回的 future 记录在这个实例的成员变量 self._connect_future 中.
然后执行 socket 的 connect 操作,因为 socket 设置成非阻塞,
所以此处会立即返回,不会阻塞,当连接成功时,缓冲区可写,失败时缓冲区可读可写.这是基础知识,详情百度.
然后调用 self._add_io_state ,返回 future
_add_io_state
def _add_io_state(self, state):
if self.closed():
# connection has been closed, so there can be no future events
return
if self._state is None:
self._state = ioloop.IOLoop.ERROR | state
with stack_context.NullContext():
self.io_loop.add_handler(
self.fileno(), self._handle_events, self._state)
elif not self._state & state:
self._state = self._state | state
self.io_loop.update_handler(self.fileno(), self._state)
终于到了这一步,要用 epoll 了!!!根据实例化的代码得知 self._state=None ,
会走 self.io_loop.add_handler 这步,根据我之前发的[文章][2],会将当前的 fd ,当前实例的 _handle_events ,和写,错误操作注册到 epoll 中
接着!!!!!终于走完了这个 yield 的流程了!!!!!!
###小总结:
请一定弄清 future 是怎么传递的,每个 future 管理的 callback 是什么操作.
_HTTPConnection 中 tcpclient.connect 一个 future ,callback=self._on_connect .
他将在 raise gen.Return(stream )时被添加到 ioloop 执行.
tcpclient.connect 内部的 connector.start 一个 future ,
callback 是 on_connect_done ,他将在 poll 检测到 write 事件时,被添加到 ioloop 执行
ioloop
def start(self):
if self._running:
raise RuntimeError("IOLoop is already running")
self._setup_logging()
if self._stopped:
self._stopped = False
return
old_current = getattr(IOLoop._current, "instance", None)
IOLoop._current.instance = self
self._thread_ident = thread.get_ident()
self._running = True
old_wakeup_fd = None
if hasattr(signal, 'set_wakeup_fd') and os.name == 'posix':
try:
old_wakeup_fd = signal.set_wakeup_fd(self._waker.write_fileno())
if old_wakeup_fd != -1:
signal.set_wakeup_fd(old_wakeup_fd)
old_wakeup_fd = None
except ValueError:
old_wakeup_fd = None
try:
while True:
with self._callback_lock:
callbacks = self._callbacks
self._callbacks = []
due_timeouts = []
if self._timeouts:
now = self.time()
while self._timeouts:
if self._timeouts[0].callback is None:
heapq.heappop(self._timeouts)
self._cancellations -= 1
elif self._timeouts[0].deadline <= now:
due_timeouts.append(heapq.heappop(self._timeouts))
else:
break
if (self._cancellations > 512
and self._cancellations > (len(self._timeouts) >> 1)):
self._cancellations = 0
self._timeouts = [x for x in self._timeouts
if x.callback is not None]
heapq.heapify(self._timeouts)
for callback in callbacks:
self._run_callback(callback)
for timeout in due_timeouts:
if timeout.callback is not None:
self._run_callback(timeout.callback)
callbacks = callback = due_timeouts = timeout = None
if self._callbacks:
poll_timeout = 0.0
elif self._timeouts:
poll_timeout = self._timeouts[0].deadline - self.time()
poll_timeout = max(0, min(poll_timeout, _POLL_TIMEOUT))
else:
poll_timeout = _POLL_TIMEOUT
if not self._running:
break
if self._blocking_signal_threshold is not None:
signal.setitimer(signal.ITIMER_REAL, 0, 0)
try:
event_pairs = self._impl.poll(poll_timeout)
except Exception as e:
if errno_from_exception(e) == errno.EINTR:
continue
else:
raise
if self._blocking_signal_threshold is not None:
signal.setitimer(signal.ITIMER_REAL,
self._blocking_signal_threshold, 0)
self._events.update(event_pairs)
while self._events:
fd, events = self._events.popitem()
try:
fd_obj, handler_func = self._handlers[fd]
handler_func(fd_obj, events)
except (OSError, IOError) as e:
if errno_from_exception(e) == errno.EPIPE:
# Happens when the client closes the connection
pass
else:
self.handle_callback_exception(self._handlers.get(fd))
except Exception:
self.handle_callback_exception(self._handlers.get(fd))
fd_obj = handler_func = None
finally:
# 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)
IOLoop._current.instance = old_current
if old_wakeup_fd is not None:
signal.set_wakeup_fd(old_wakeup_fd)
接下来 tornado 终于也回到了 ioloop 代码中了(泪奔)!!当连接成功时,该 fd 的缓冲区可写,
epoll 收到 fd 的 write 操作通知~进入到了 epoll 的 loop 中处理.然后!回到刚才注册的 _handle_events 了!
注意这个 _handle_events 是 IOStream 的实例里的 _handle_events ,他有刚才我们处理的所有信息哦~
接下来看 _handle_events 的代码,看他如果解决掉 future
IOStream._handle_events
def _handle_events(self, fd, events):
if self.closed():
gen_log.warning("Got events for closed stream %s", fd)
return
try:
if self._connecting:
# Most IOLoops will report a write failed connect
# with the WRITE event, but SelectIOLoop reports a
# READ as well so we must check for connecting before
# either.
self._handle_connect()
if self.closed():
return
if events & self.io_loop.READ:
self._handle_read()
if self.closed():
return
if events & self.io_loop.WRITE:
self._handle_write()
if self.closed():
return
if events & self.io_loop.ERROR:
self.error = self.get_fd_error()
# We may have queued up a user callback in _handle_read or
# _handle_write, so don't close the IOStream until those
# callbacks have had a chance to run.
self.io_loop.add_callback(self.close)
return
state = self.io_loop.ERROR
if self.reading():
state |= self.io_loop.READ
if self.writing():
state |= self.io_loop.WRITE
if state == self.io_loop.ERROR and self._read_buffer_size == 0:
# If the connection is idle, listen for reads too so
# we can tell if the connection is closed. If there is
# data in the read buffer we won't run the close callback
# yet anyway, so we don't need to listen in this case.
state |= self.io_loop.READ
if state != self._state:
assert self._state is not None, \
"shouldn't happen: _handle_events without self._state"
self._state = state
self.io_loop.update_handler(self.fileno(), self._state)
except UnsatisfiableReadError as e:
gen_log.info("Unsatisfiable read, closing connection: %s" % e)
self.close(exc_info=True)
except Exception:
gen_log.error("Uncaught exception, closing connection.",
exc_info=True)
self.close(exc_info=True)
raise
def _handle_connect(self):
err = self.socket.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
if err != 0:
self.error = socket.error(err, os.strerror(err))
# IOLoop implementations may vary: some of them return
# an error state before the socket becomes writable, so
# in that case a connection failure would be handled by the
# error path in _handle_events instead of here.
if self._connect_future is None:
gen_log.warning("Connect error on fd %s: %s",
self.socket.fileno(), errno.errorcode[err])
self.close()
return
if self._connect_callback is not None:
callback = self._connect_callback
self._connect_callback = None
self._run_callback(callback)
if self._connect_future is not None:
future = self._connect_future
self._connect_future = None
future.set_result(self)
self._connecting = False
判断是否在连接中,当然是了,刚才我也强调过了,
然后进入 _handle_connect,_handle_connect 先判断 connect 有没成功,
成功了就是设置 _connect_future 的 result,set_result(self ),把 self(iostream )设置进去了!
然后 _connect_future 的 callbacks 会在下一次循环被 ioloop 消化掉!!
一步步返回看,这个 future 正是我们之前的那个 yiled 操作的右边的返回的 future ,
所以刚才 _Connector.try_connect 设置的 callback ,on_connect_done 会在 ioloop 的 callback 里执行.
根据上一篇[文章][3]讲的 coroutine 的源码得知,此 future 里还有 Runner.run 的 callback 哦~
所以 ,run 里 send 了 vaule 到 gen .
终于终于!!程序回到了刚才的 yield 处了!!!!!
tornado正是如此实现异步io的
##总结 感觉一直讲完整个操作不太现实,剩下的大家还是自己跟踪吧,道理跟这个流程类似. yield 操作右边,一定是返回一个 future (旧版本貌似是 YieldPoint ,因为没看过旧版,所以不太清楚) , 然后在返回 future 之前,设置好 fd 的 handler ,和其他的解析工作,然后等待 epoll 检测到关心的 io event , 在 io 的 handler 里把 future 解决,从而回到 yield 处~ 核心就是 ioloop 三部分 ,future,gen.coroutine . 相互配合完成异步操作. 跟踪几遍消化一下,就可以写 tornado 的扩展了.
祝大家武运亨通
来源：oschina
链接：https://my.oschina.net/u/874613/blog/477569