tornado 源码阅读-初步认识

摘要：序言最近闲暇无事阅读了一下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吧是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的核心部分则是这个循环内部的逻辑贴

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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]

</>复制代码 
`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

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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

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   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)

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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:

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

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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

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

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

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

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

跟ioloop的callback类似 , 存储事件完成后的callback在self._callbacks里

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def add_done_callback(self, fn):
        if self._done:
            fn(self)
        else:
            self._callbacks.append(fn)

设置事件的结果,并运行之前存储好的callback

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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

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#! /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:

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:

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#! /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:

接下来分析下coroutine的实现

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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.

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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

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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

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if not self.handle_yield(yielded):
                    return

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,

啊~~~~~~好想有份工作 和女朋友啊~~~~~