序言
最近闲暇无事,阅读了一下tornado的源码,对整体的结构有了初步认识,与大家分享
不知道为什么右边的目录一直出不来,非常不舒服.
不如移步到oschina吧....[http://my.oschina.net/abc2001x/blog/476349][1]
ioloop
`ioloop`是`tornado`的核心模块,也是个调度模块,各种异步事件都是由他调度的,所以必须弄清他的执行逻辑
源码分析
而`ioloop`的核心部分则是 `while True`这个循环内部的逻辑,贴上他的代码如下
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:
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:
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)
除去注释,代码其实没多少行. 由while 内部代码可以看出ioloop主要由三部分组成:
1.回调 callbacks
他是ioloop回调的基础部分,通过IOLoop.instance().add_callback()添加到self._callbacks
他们将在每一次loop中被运行.
主要用途是将逻辑分块,在适合时机将包装好的callback添加到self._callbacks让其执行.
例如ioloop中的add_future
def add_future(self, future, callback):
"""Schedules a callback on the ``IOLoop`` when the given
`.Future` is finished.
The callback is invoked with one argument, the
`.Future`.
"""
assert is_future(future)
callback = stack_context.wrap(callback)
future.add_done_callback(
lambda future: self.add_callback(callback, future))
future对象得到result的时候会调用future.add_done_callback添加的callback,再将其转至ioloop执行
2.定时器 due_timeouts
这是定时器,在指定的事件执行callback.
跟1中的callback类似,通过IOLoop.instance().add_callback
在每一次循环,会计算timeouts回调列表里的事件,运行已到期的callback.
当然不是无节操的循环.
因为poll操作会阻塞到有io操作发生,所以只要计算最近的timeout,
然后用这个时间作为self._impl.poll(poll_timeout) 的 poll_timeout ,
就可以达到按时运行了
但是,假设poll_timeout的时间很大时,self._impl.poll一直在堵塞中(没有io事件,但在处理某一个io事件),
那添加刚才1中的callback不是要等很久才会被运行吗? 答案当然是不会.ioloop中有个waker对象,他是由两个fd组成,一个读一个写.ioloop在初始化的时候把waker绑定到epoll里了,add_callback时会触发waker的读写.
这样ioloop就会在poll中被唤醒了,接着就可以及时处理timeout callback了
用这样的方式也可以自己封装一个小的定时器功能玩玩
3.io事件的event loop
处理epoll事件的功能
通过IOLoop.instance().add_handler(fd, handler, events)绑定fd event的处理事件
在httpserver.listen的代码内,netutil.py中的netutil.py的add_accept_handler绑定accept handler处理客户端接入的逻辑
如法炮制,其他的io事件也这样绑定,业务逻辑的分块交由ioloop的callback和future处理
关于epoll的用法的内容.详情见我第一篇文章吧,哈哈
总结
ioloop由callback(业务分块), timeout callback(定时任务) io event(io传输和解析) 三块组成,互相配合完成异步的功能,构建gen,httpclient,iostream等功能
串联大致的流程是,tornado 绑定io event,处理io传输解析,传输完成后(结合Future)回调(callback)业务处理的逻辑和一些固定操作 . 定时器则是较为独立的模块
Futrue
个人认为Future是tornado仅此ioloop重要的模块,他贯穿全文,所有异步操作都有他的身影
顾名思义,他主要是关注日后要做的事,类似jquery的Deferred吧
一般的用法是通过ioloop的add_future定义future的done callback,
当future被set_result的时候,future的done callback就会被调用.
从而完成Future的功能.
具体可以参考gen.coroutine的实现,本文后面也会讲到
他的组成不复杂,只有几个重要的方法
最重要的是 add_done_callback , set_result
tornado用Future和ioloop,yield实现了gen.coroutine
1. add_done_callback
跟ioloop的callback类似 , 存储事件完成后的callback在self._callbacks里
def add_done_callback(self, fn):
if self._done:
fn(self)
else:
self._callbacks.append(fn)
2.set_result
设置事件的结果,并运行之前存储好的callback
def set_result(self, result):
self._result = result
self._set_done()
def _set_done(self):
self._done = True
for cb in self._callbacks:
try:
cb(self)
except Exception:
app_log.exception('Exception in callback %r for %r',
cb, self)
self._callbacks = None
为了验证之前所说的,上一段测试代码
#! /usr/bin/env python
#coding=utf-8
import tornado.web
import tornado.ioloop
from tornado.gen import coroutine
from tornado.concurrent import Future
def test():
def pp(s):
print s
future = Future()
iol = tornado.ioloop.IOLoop.instance()
print 'init future %s'%future
iol.add_future(future, lambda f: pp('ioloop callback after future done,future is %s'%f))
#模拟io延迟操作
iol.add_timeout(iol.time()+5,lambda:future.set_result('set future is done'))
print 'init complete'
tornado.ioloop.IOLoop.instance().start()
if __name__ == "__main__":
test()
运行结果:
gen.coroutine
接着继续延伸,看看coroutine的实现gen.coroutine实现的功能其实是将原来的callback的写法,用yield的写法代替. 即以yield为分界,将代码分成两部分.
如:
#! /usr/bin/env python
#coding=utf-8
import tornado.ioloop
from tornado.gen import coroutine
from tornado.httpclient import AsyncHTTPClient
@coroutine
def cotest():
client = AsyncHTTPClient()
res = yield client.fetch("http://www.segmentfault.com/")
print res
if __name__ == "__main__":
f = cotest()
print f #这里返回了一个future哦
tornado.ioloop.IOLoop.instance().start()
运行结果:
源码分析
接下来分析下coroutine的实现
def _make_coroutine_wrapper(func, replace_callback):
@functools.wraps(func)
def wrapper(*args, **kwargs):
future = TracebackFuture()
if replace_callback and 'callback' in kwargs:
callback = kwargs.pop('callback')
IOLoop.current().add_future(
future, lambda future: callback(future.result()))
try:
result = func(*args, **kwargs)
except (Return, StopIteration) as e:
result = getattr(e, 'value', None)
except Exception:
future.set_exc_info(sys.exc_info())
return future
else:
if isinstance(result, types.GeneratorType):
try:
orig_stack_contexts = stack_context._state.contexts
yielded = next(result)
if stack_context._state.contexts is not orig_stack_contexts:
yielded = TracebackFuture()
yielded.set_exception(
stack_context.StackContextInconsistentError(
'stack_context inconsistency (probably caused '
'by yield within a "with StackContext" block)'))
except (StopIteration, Return) as e:
future.set_result(getattr(e, 'value', None))
except Exception:
future.set_exc_info(sys.exc_info())
else:
Runner(result, future, yielded)
try:
return future
finally:
future = None
future.set_result(result)
return future
return wrapper
如源码所示,func运行的结果是GeneratorType ,yielded = next(result),
运行至原函数的yield位置,返回的是原函数func内部 yield 右边返回的对象(必须是Future或Future的list)给yielded.
经过Runner(result, future, yielded) 对yielded进行处理.
在此就 贴出Runner的代码了.
Runner初始化过程,调用handle_yield, 查看yielded是否已done了,否则add_future运行Runner的run方法,run方法中如果yielded对象已完成,用对它的gen调用send,发送完成的结果.
所以yielded在什么地方被set_result非常重要,
当被set_result的时候,才会send结果给原func,完成整个异步操作
详情可以查看tornado 中重要的对象 iostream,源码中iostream的 _handle_connect,如此设置了连接的result.
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))
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
最后贴上一个简单的测试代码,演示coroutine,future的用法
import tornado.ioloop
from tornado.gen import coroutine
from tornado.concurrent import Future
@coroutine
def asyn_sum(a, b):
print("begin calculate:sum %d+%d"%(a,b))
future = Future()
future2 = Future()
iol = tornado.ioloop.IOLoop.instance()
print future
def callback(a, b):
print("calculating the sum of %d+%d:"%(a,b))
future.set_result(a+b)
iol.add_timeout(iol.time()+3,lambda f:f.set_result(None),future2)
iol.add_timeout(iol.time()+3,callback, a, b)
result = yield future
print("after yielded")
print("the %d+%d=%d"%(a, b, result))
yield future2
print 'after future2'
def main():
f = asyn_sum(2,3)
print ''
print f
tornado.ioloop.IOLoop.instance().start()
if __name__ == "__main__":
main()
运行结果:
为什么代码中个yield都起作用了? 因为Runner.run里,最后继续用handle_yield处理了send后返回的yielded对象,意思是func里可以有n干个yield操作
if not self.handle_yield(yielded):
return
总结
至此,已完成tornado中重要的几个模块的流程,其他模块也是由此而来.写了这么多,越写越卡,就到此为止先吧,
最后的最后的最后
啊~~~~~~好想有份工作 和女朋友啊~~~~~