深入tornado中的协程

class Future(object):
    ‘‘‘
        Future对象主要保存一个回调函数列表_callbacks与一个执行结果_result，当我们set_result时，就会执行_callbacks中的函数
    ‘‘‘
    def __init__(self):
        self._done = False  # 是否执行完成
        self._result = None    # 执行的结果
        self._exc_info = None    # 执行的异常信息

        self._log_traceback = False   # Used for Python >= 3.4
        self._tb_logger = None        # Used for Python <= 3.3

        self._callbacks = []    # 用来保存该future对象的回调函数

    # Implement the Python 3.5 Awaitable protocol if possible
    # (we can‘t use return and yield together until py33).
    if sys.version_info >= (3, 3):
        exec(textwrap.dedent("""
        def __await__(self):
            return (yield self)
        """))
    else:
        # Py2-compatible version for use with cython.
        def __await__(self):
            result = yield self
            # StopIteration doesn‘t take args before py33,
            # but Cython recognizes the args tuple.
            e = StopIteration()
            e.args = (result,)
            raise e

    def cancel(self):
        """Cancel the operation, if possible. 如果可能的话取消操作
        tornado对象不支持取消操作，所以总是返回False
        """
        return False

    def cancelled(self):
        # 同上
        return False

    def running(self):
        """Returns True if this operation is currently running."""
        return not self._done

    def done(self):
        """Returns True if the future has finished running."""
        return self._done

    def _clear_tb_log(self):
        self._log_traceback = False
        if self._tb_logger is not None:
            self._tb_logger.clear()
            self._tb_logger = None

    def result(self, timeout=None):
        """If the operation succeeded, return its result.  If it failed,
        re-raise its exception. 如果操作成功，返回结果。如果失败则抛出异常

        This method takes a ``timeout`` argument for compatibility with
        `concurrent.futures.Future` but it is an error to call it
        before the `Future` is done, so the ``timeout`` is never used.
        """
        self._clear_tb_log()
        if self._result is not None:
            return self._result
        if self._exc_info is not None:
            raise_exc_info(self._exc_info)
        self._check_done()
        return self._result

    def exception(self, timeout=None):
        """If the operation raised an exception, return the `Exception`
        object.  Otherwise returns None.

        This method takes a ``timeout`` argument for compatibility with
        `concurrent.futures.Future` but it is an error to call it
        before the `Future` is done, so the ``timeout`` is never used.
        """
        self._clear_tb_log()
        if self._exc_info is not None:
            return self._exc_info[1]
        else:
            self._check_done()
            return None

    def add_done_callback(self, fn):
        """Attaches the given callback to the `Future`. 将callback附加到

        It will be invoked with the `Future` as its argument when the Future
        has finished running and its result is available.  In Tornado
        consider using `.IOLoop.add_future` instead of calling
        `add_done_callback` directly.
        """
        if self._done:
            fn(self)
        else:
            self._callbacks.append(fn)

    def set_result(self, result):
        """Sets the result of a ``Future``. 将 result 设置为该future对象的结果

        It is undefined to call any of the ``set`` methods more than once
        on the same object.
        """
        self._result = result
        self._set_done()

    def set_exception(self, exception):
        """Sets the exception of a ``Future.``"""
        self.set_exc_info(
            (exception.__class__,
             exception,
             getattr(exception, ‘__traceback__‘, None)))

    def exc_info(self):
        """Returns a tuple in the same format as `sys.exc_info` or None.

        .. versionadded:: 4.0
        """
        self._clear_tb_log()
        return self._exc_info

    def set_exc_info(self, exc_info):
        """Sets the exception information of a ``Future.``

        Preserves tracebacks on Python 2.

        .. versionadded:: 4.0
        """
        self._exc_info = exc_info
        self._log_traceback = True
        if not _GC_CYCLE_FINALIZERS:
            self._tb_logger = _TracebackLogger(exc_info)

        try:
            self._set_done()
        finally:
            # Activate the logger after all callbacks have had a
            # chance to call result() or exception().
            if self._log_traceback and self._tb_logger is not None:
                self._tb_logger.activate()
        self._exc_info = exc_info

    def _check_done(self):
        if not self._done:
            raise Exception("DummyFuture does not support blocking for results")

    def _set_done(self):
        # 执行结束(成功)后的操作。
        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

    # On Python 3.3 or older, objects with a destructor part of a reference
    # cycle are never destroyed. It‘s no longer the case on Python 3.4 thanks to
    # the PEP 442.
    if _GC_CYCLE_FINALIZERS:
        def __del__(self):
            if not self._log_traceback:
                # set_exception() was not called, or result() or exception()
                # has consumed the exception
                return

            tb = traceback.format_exception(*self._exc_info)

            app_log.error(‘Future %r exception was never retrieved: %s‘,
                          self, ‘‘.join(tb).rstrip())

def run():
    print(‘start running‘)
    yield 2     # 跑步用时2小时

def eat():
    print(‘start eating‘)
    yield 1     # 吃饭用时1小时

def time():
    run_time = yield run()
    eat_time = yield eat()
    print(run_time+eat_time)

def Runner(gen):
    r = next(gen)
    return r

t = time()
try:
    action = t.send(Runner(next(t)))
    t.send(Runner(action))
except StopIteration:
    pass

class Runner(object):
    def __init__(self, gen, result_future, first_yielded):
        self.gen = gen                        # 一个generator对象
        self.result_future = result_future    # 一个Future对象
        self.future = _null_future            # 一个刚初始化的Future对象  _null_future = Future(); _null_future.set_result(None)
        self.yield_point = None
        self.pending_callbacks = None
        self.results = None
        self.running = False
        self.finished = False
        self.had_exception = False
        self.io_loop = IOLoop.current()
        self.stack_context_deactivate = None
        if self.handle_yield(first_yielded):
            self.run()
    
    ………… 部分方法省略
    def run(self):
        """Starts or resumes the generator, running until it reaches a
        yield point that is not ready.
        """
        if self.running or self.finished:
            return
        try:
            self.running = True
            while True:
                future = self.future
                if not future.done():
                    return
                self.future = None
                try:
                    orig_stack_contexts = stack_context._state.contexts
                    exc_info = None

                    try:
                        value = future.result()
                    except Exception:
                        self.had_exception = True
                        exc_info = sys.exc_info()

                    if exc_info is not None:
                        yielded = self.gen.throw(*exc_info)
                        exc_info = None
                    else:
                        yielded = self.gen.send(value)

                    if stack_context._state.contexts is not orig_stack_contexts:
                        self.gen.throw(
                            stack_context.StackContextInconsistentError(
                                ‘stack_context inconsistency (probably caused ‘
                                ‘by yield within a "with StackContext" block)‘))
                except (StopIteration, Return) as e:
                    self.finished = True
                    self.future = _null_future
                    if self.pending_callbacks and not self.had_exception:
                        # If we ran cleanly without waiting on all callbacks
                        # raise an error (really more of a warning).  If we
                        # had an exception then some callbacks may have been
                        # orphaned, so skip the check in that case.
                        raise LeakedCallbackError(
                            "finished without waiting for callbacks %r" %
                            self.pending_callbacks)
                    self.result_future.set_result(_value_from_stopiteration(e))
                    self.result_future = None
                    self._deactivate_stack_context()
                    return
                except Exception:
                    self.finished = True
                    self.future = _null_future
                    self.result_future.set_exc_info(sys.exc_info())
                    self.result_future = None
                    self._deactivate_stack_context()
                    return
                if not self.handle_yield(yielded):
                    return
        finally:
            self.running = False

    def handle_yield(self, yielded):
        if _contains_yieldpoint(yielded):    # 检查其中是否包含YieldPoint
            yielded = multi(yielded)

        if isinstance(yielded, YieldPoint):        # Base class for objects that may be yielded from the generator
            self.future = TracebackFuture()        # 一个刚刚初始化的Future对象

            def start_yield_point():
                try:
                    yielded.start(self)
                    if yielded.is_ready():
                        self.future.set_result(yielded.get_result())
                    else:
                        self.yield_point = yielded
                except Exception:
                    self.future = TracebackFuture()
                    self.future.set_exc_info(sys.exc_info())

            if self.stack_context_deactivate is None:
                with stack_context.ExceptionStackContext(self.handle_exception) as deactivate:
                    self.stack_context_deactivate = deactivate
                    
                    def cb():
                        start_yield_point()
                        self.run()
                    self.io_loop.add_callback(cb)
                    return False
            else:
                start_yield_point()
        else:
            try:
                self.future = convert_yielded(yielded)
            except BadYieldError:
                self.future = TracebackFuture()
                self.future.set_exc_info(sys.exc_info())

        if not self.future.done() or self.future is moment:  # moment = Future()
            self.io_loop.add_future(self.future, lambda f: self.run()) # 为该future添加callback
            return False
        return True