tornado 源碼閱讀-初步認識

序言

最近閒暇無事,閱讀了一下tornado的源碼,對總體的結構有了初步認識,與你們分享
不知道爲何右邊的目錄一直出不來,很是不舒服.
不如移步到oschina吧....[http://my.oschina.net/abc2001x/blog/476349][1]

ioloop

`ioloop`是`tornado`的核心模塊,也是個調度模塊,各類異步事件都是由他調度的,因此必須弄清他的執行邏輯

源碼分析

而`ioloop`的核心部分則是 `while True`這個循環內部的邏輯,貼上他的代碼以下

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)

除去註釋,代碼其實沒多少行. 由while 內部代碼能夠看出ioloop主要由三部分組成:

1.回調 callbacks

他是ioloop回調的基礎部分,經過IOLoop.instance().add_callback()添加到self._callbacks
他們將在每一次loop中被運行.

主要用途是將邏輯分塊,在適合時機將包裝好的callback添加到self._callbacks讓其執行.

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對象獲得result的時候會調用future.add_done_callback添加的callback,再將其轉至ioloop執行

2.定時器 due_timeouts

這是定時器,在指定的事件執行callback.
跟1中的callback相似,經過IOLoop.instance().add_callback

在每一次循環,會計算timeouts回調列表裏的事件,運行已到期的callback.
固然不是無節操的循環.

由於poll操做會阻塞到有io操做發生,因此只要計算最近的timeout,
而後用這個時間做爲self._impl.poll(poll_timeout) 的 poll_timeout ,
就能夠達到按時運行了

可是,假設poll_timeout的時間很大時,self._impl.poll一直在堵塞中(沒有io事件,但在處理某一個io事件),
那添加剛纔1中的callback不是要等好久纔會被運行嗎? 答案固然是不會.
ioloop中有個waker對象,他是由兩個fd組成,一個讀一個寫.
ioloop在初始化的時候把waker綁定到epoll裏了,add_callback時會觸發waker的讀寫.
這樣ioloop就會在poll中被喚醒了,接着就能夠及時處理timeout callback了

用這樣的方式也能夠本身封裝一個小的定時器功能玩玩

3.io事件的event loop

處理epoll事件的功能
經過IOLoop.instance().add_handler(fd, handler, events)綁定fd event的處理事件
在httpserver.listen的代碼內,
netutil.py中的netutil.py的add_accept_handler綁定accept handler處理客戶端接入的邏輯

如法炮製,其餘的io事件也這樣綁定,業務邏輯的分塊交由ioloop的callback和future處理

關於epoll的用法的內容.詳情見我第一篇文章吧,哈哈

總結

ioloop由callback(業務分塊), timeout callback(定時任務) io event(io傳輸和解析) 三塊組成,互相配合完成異步的功能,構建gen,httpclient,iostream等功能

串聯大體的流程是,tornado 綁定io event,處理io傳輸解析,傳輸完成後(結合Future)回調(callback)業務處理的邏輯和一些固定操做 . 定時器則是較爲獨立的模塊

Futrue

我的認爲Future是tornado僅此ioloop重要的模塊,他貫穿全文,全部異步操做都有他的身影
顧名思義,他主要是關注往後要作的事,相似jquery的Deferred吧

通常的用法是經過ioloop的add_future定義future的done callback,
當future被set_result的時候,future的done callback就會被調用.
從而完成Future的功能.

具體能夠參考gen.coroutine的實現,本文後面也會講到

他的組成不復雜,只有幾個重要的方法
最重要的是 add_done_callback , set_result

tornado用Future和ioloop,yield實現了gen.coroutine

1. add_done_callback

跟ioloop的callback相似 , 存儲事件完成後的callback在self._callbacks裏

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

2.set_result

設置事件的結果,並運行以前存儲好的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

爲了驗證以前所說的,上一段測試代碼

#! /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))

    #模擬io延遲操做
    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()

運行結果:

gen.coroutine

接着繼續延伸,看看coroutine的實現
gen.coroutine實現的功能實際上是將原來的callback的寫法,用yield的寫法代替. 即以yield爲分界,將代碼分紅兩部分.
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 #這裏返回了一個future哦
    tornado.ioloop.IOLoop.instance().start()

運行結果:

源碼分析

接下來分析下coroutine的實現

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

如源碼所示,func運行的結果是GeneratorType ,yielded = next(result),
運行至原函數的yield位置,返回的是原函數func內部 yield 右邊返回的對象(必須是Future或Future的list)給yielded.
通過Runner(result, future, yielded) 對yielded進行處理.
在此就 貼出Runner的代碼了.
Runner初始化過程,調用handle_yield, 查看yielded是否已done了,不然add_future運行Runner的run方法,
run方法中若是yielded對象已完成,用對它的gen調用send,發送完成的結果.
因此yielded在什麼地方被set_result很是重要,
當被set_result的時候,纔會send結果給原func,完成整個異步操做

詳情能夠查看tornado 中重要的對象 iostream,源碼中iostream的 _handle_connect,如此設置了鏈接的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

最後貼上一個簡單的測試代碼,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()

運行結果:

爲何代碼中個yield都起做用了? 由於Runner.run裏,最後繼續用handle_yield處理了send後返回的yielded對象,意思是func裏能夠有n幹個yield操做

if not self.handle_yield(yielded):
                    return

總結

至此,已完成tornado中重要的幾個模塊的流程,其餘模塊也是由此而來.寫了這麼多,越寫越卡,就到此爲止先吧,

最後的最後的最後

啊~~~~~~好想有份工做 和女友啊~~~~~