tornado 源码阅读-初步认识

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~~~~~