asyncio.tasks 源代码

"""Support for tasks, coroutines and the scheduler."""

__all__ = (
    'Task', 'create_task',
    'wait', 'wait_for', 'as_completed', 'sleep',
    'gather', 'shield', 'ensure_future', 'run_coroutine_threadsafe',
    'current_task', 'all_tasks',
    '_register_task', '_unregister_task', '_enter_task', '_leave_task',

import concurrent.futures
import contextvars
import functools
import inspect
import types
import warnings
import weakref

from . import base_tasks
from . import coroutines
from . import events
from . import futures
from .coroutines import coroutine

def current_task(loop=None):
    """Return a currently executed task."""
    if loop is None:
        loop = events.get_running_loop()
    return _current_tasks.get(loop)

def all_tasks(loop=None):
    """Return a set of all tasks for the loop."""
    if loop is None:
        loop = events.get_running_loop()
    # NB: set(_all_tasks) is required to protect
    # from bug
    return {t for t in list(_all_tasks)
            if futures._get_loop(t) is loop and not t.done()}

def _all_tasks_compat(loop=None):
    # Different from "all_task()" by returning *all* Tasks, including
    # the completed ones.  Used to implement deprecated "Tasks.all_task()"
    # method.
    if loop is None:
        loop = events.get_event_loop()
    # NB: set(_all_tasks) is required to protect
    # from bug
    return {t for t in list(_all_tasks) if futures._get_loop(t) is loop}

class Task(futures._PyFuture):  # Inherit Python Task implementation
                                # from a Python Future implementation.

    """A coroutine wrapped in a Future."""

    # An important invariant maintained while a Task not done:
    # - Either _fut_waiter is None, and _step() is scheduled;
    # - or _fut_waiter is some Future, and _step() is *not* scheduled.
    # The only transition from the latter to the former is through
    # _wakeup().  When _fut_waiter is not None, one of its callbacks
    # must be _wakeup().

    # If False, don't log a message if the task is destroyed whereas its
    # status is still pending
    _log_destroy_pending = True

    def current_task(cls, loop=None):
        """Return the currently running task in an event loop or None.

        By default the current task for the current event loop is returned.

        None is returned when called not in the context of a Task.
        warnings.warn("Task.current_task() is deprecated, "
                      "use asyncio.current_task() instead",
        if loop is None:
            loop = events.get_event_loop()
        return current_task(loop)

    def all_tasks(cls, loop=None):
        """Return a set of all tasks for an event loop.

        By default all tasks for the current event loop are returned.
        warnings.warn("Task.all_tasks() is deprecated, "
                      "use asyncio.all_tasks() instead",
        return _all_tasks_compat(loop)

    def __init__(self, coro, *, loop=None):
        if self._source_traceback:
            del self._source_traceback[-1]
        if not coroutines.iscoroutine(coro):
            # raise after Future.__init__(), attrs are required for __del__
            # prevent logging for pending task in __del__
            self._log_destroy_pending = False
            raise TypeError(f"a coroutine was expected, got {coro!r}")

        self._must_cancel = False
        self._fut_waiter = None
        self._coro = coro
        self._context = contextvars.copy_context()

        self._loop.call_soon(self.__step, context=self._context)

    def __del__(self):
        if self._state == futures._PENDING and self._log_destroy_pending:
            context = {
                'task': self,
                'message': 'Task was destroyed but it is pending!',
            if self._source_traceback:
                context['source_traceback'] = self._source_traceback

    def _repr_info(self):
        return base_tasks._task_repr_info(self)

    def set_result(self, result):
        raise RuntimeError('Task does not support set_result operation')

    def set_exception(self, exception):
        raise RuntimeError('Task does not support set_exception operation')

    def get_stack(self, *, limit=None):
        """Return the list of stack frames for this task's coroutine.

        If the coroutine is not done, this returns the stack where it is
        suspended.  If the coroutine has completed successfully or was
        cancelled, this returns an empty list.  If the coroutine was
        terminated by an exception, this returns the list of traceback

        The frames are always ordered from oldest to newest.

        The optional limit gives the maximum number of frames to
        return; by default all available frames are returned.  Its
        meaning differs depending on whether a stack or a traceback is
        returned: the newest frames of a stack are returned, but the
        oldest frames of a traceback are returned.  (This matches the
        behavior of the traceback module.)

        For reasons beyond our control, only one stack frame is
        returned for a suspended coroutine.
        return base_tasks._task_get_stack(self, limit)

    def print_stack(self, *, limit=None, file=None):
        """Print the stack or traceback for this task's coroutine.

        This produces output similar to that of the traceback module,
        for the frames retrieved by get_stack().  The limit argument
        is passed to get_stack().  The file argument is an I/O stream
        to which the output is written; by default output is written
        to sys.stderr.
        return base_tasks._task_print_stack(self, limit, file)

    def cancel(self):
        """Request that this task cancel itself.

        This arranges for a CancelledError to be thrown into the
        wrapped coroutine on the next cycle through the event loop.
        The coroutine then has a chance to clean up or even deny
        the request using try/except/finally.

        Unlike Future.cancel, this does not guarantee that the
        task will be cancelled: the exception might be caught and
        acted upon, delaying cancellation of the task or preventing
        cancellation completely.  The task may also return a value or
        raise a different exception.

        Immediately after this method is called, Task.cancelled() will
        not return True (unless the task was already cancelled).  A
        task will be marked as cancelled when the wrapped coroutine
        terminates with a CancelledError exception (even if cancel()
        was not called).
        self._log_traceback = False
        if self.done():
            return False
        if self._fut_waiter is not None:
            if self._fut_waiter.cancel():
                # Leave self._fut_waiter; it may be a Task that
                # catches and ignores the cancellation so we may have
                # to cancel it again later.
                return True
        # It must be the case that self.__step is already scheduled.
        self._must_cancel = True
        return True

    def __step(self, exc=None):
        if self.done():
            raise futures.InvalidStateError(
                f'_step(): already done: {self!r}, {exc!r}')
        if self._must_cancel:
            if not isinstance(exc, futures.CancelledError):
                exc = futures.CancelledError()
            self._must_cancel = False
        coro = self._coro
        self._fut_waiter = None

        _enter_task(self._loop, self)
        # Call either coro.throw(exc) or coro.send(None).
            if exc is None:
                # We use the `send` method directly, because coroutines
                # don't have `__iter__` and `__next__` methods.
                result = coro.send(None)
                result = coro.throw(exc)
        except StopIteration as exc:
            if self._must_cancel:
                # Task is cancelled right before coro stops.
                self._must_cancel = False
        except futures.CancelledError:
            super().cancel()  # I.e., Future.cancel(self).
        except Exception as exc:
        except BaseException as exc:
            blocking = getattr(result, '_asyncio_future_blocking', None)
            if blocking is not None:
                # Yielded Future must come from Future.__iter__().
                if futures._get_loop(result) is not self._loop:
                    new_exc = RuntimeError(
                        f'Task {self!r} got Future '
                        f'{result!r} attached to a different loop')
                        self.__step, new_exc, context=self._context)
                elif blocking:
                    if result is self:
                        new_exc = RuntimeError(
                            f'Task cannot await on itself: {self!r}')
                            self.__step, new_exc, context=self._context)
                        result._asyncio_future_blocking = False
                            self.__wakeup, context=self._context)
                        self._fut_waiter = result
                        if self._must_cancel:
                            if self._fut_waiter.cancel():
                                self._must_cancel = False
                    new_exc = RuntimeError(
                        f'yield was used instead of yield from '
                        f'in task {self!r} with {result!r}')
                        self.__step, new_exc, context=self._context)

            elif result is None:
                # Bare yield relinquishes control for one event loop iteration.
                self._loop.call_soon(self.__step, context=self._context)
            elif inspect.isgenerator(result):
                # Yielding a generator is just wrong.
                new_exc = RuntimeError(
                    f'yield was used instead of yield from for '
                    f'generator in task {self!r} with {result!r}')
                    self.__step, new_exc, context=self._context)
                # Yielding something else is an error.
                new_exc = RuntimeError(f'Task got bad yield: {result!r}')
                    self.__step, new_exc, context=self._context)
            _leave_task(self._loop, self)
            self = None  # Needed to break cycles when an exception occurs.

    def __wakeup(self, future):
        except Exception as exc:
            # This may also be a cancellation.
            # Don't pass the value of `future.result()` explicitly,
            # as `Future.__iter__` and `Future.__await__` don't need it.
            # If we call `_step(value, None)` instead of `_step()`,
            # Python eval loop would use `.send(value)` method call,
            # instead of `__next__()`, which is slower for futures
            # that return non-generator iterators from their `__iter__`.
        self = None  # Needed to break cycles when an exception occurs.

_PyTask = Task

    import _asyncio
except ImportError:
    # _CTask is needed for tests.
    Task = _CTask = _asyncio.Task

[文档]def create_task(coro): """Schedule the execution of a coroutine object in a spawn task. Return a Task object. """ loop = events.get_running_loop() return loop.create_task(coro)
# wait() and as_completed() similar to those in PEP 3148. FIRST_COMPLETED = concurrent.futures.FIRST_COMPLETED FIRST_EXCEPTION = concurrent.futures.FIRST_EXCEPTION ALL_COMPLETED = concurrent.futures.ALL_COMPLETED async def wait(fs, *, loop=None, timeout=None, return_when=ALL_COMPLETED): """Wait for the Futures and coroutines given by fs to complete. The sequence futures must not be empty. Coroutines will be wrapped in Tasks. Returns two sets of Future: (done, pending). Usage: done, pending = await asyncio.wait(fs) Note: This does not raise TimeoutError! Futures that aren't done when the timeout occurs are returned in the second set. """ if futures.isfuture(fs) or coroutines.iscoroutine(fs): raise TypeError(f"expect a list of futures, not {type(fs).__name__}") if not fs: raise ValueError('Set of coroutines/Futures is empty.') if return_when not in (FIRST_COMPLETED, FIRST_EXCEPTION, ALL_COMPLETED): raise ValueError(f'Invalid return_when value: {return_when}') if loop is None: loop = events.get_event_loop() fs = {ensure_future(f, loop=loop) for f in set(fs)} return await _wait(fs, timeout, return_when, loop) def _release_waiter(waiter, *args): if not waiter.done(): waiter.set_result(None) async def wait_for(fut, timeout, *, loop=None): """Wait for the single Future or coroutine to complete, with timeout. Coroutine will be wrapped in Task. Returns result of the Future or coroutine. When a timeout occurs, it cancels the task and raises TimeoutError. To avoid the task cancellation, wrap it in shield(). If the wait is cancelled, the task is also cancelled. This function is a coroutine. """ if loop is None: loop = events.get_event_loop() if timeout is None: return await fut if timeout <= 0: fut = ensure_future(fut, loop=loop) if fut.done(): return fut.result() fut.cancel() raise futures.TimeoutError() waiter = loop.create_future() timeout_handle = loop.call_later(timeout, _release_waiter, waiter) cb = functools.partial(_release_waiter, waiter) fut = ensure_future(fut, loop=loop) fut.add_done_callback(cb) try: # wait until the future completes or the timeout try: await waiter except futures.CancelledError: fut.remove_done_callback(cb) fut.cancel() raise if fut.done(): return fut.result() else: fut.remove_done_callback(cb) # We must ensure that the task is not running # after wait_for() returns. # See await _cancel_and_wait(fut, loop=loop) raise futures.TimeoutError() finally: timeout_handle.cancel() async def _wait(fs, timeout, return_when, loop): """Internal helper for wait(). The fs argument must be a collection of Futures. """ assert fs, 'Set of Futures is empty.' waiter = loop.create_future() timeout_handle = None if timeout is not None: timeout_handle = loop.call_later(timeout, _release_waiter, waiter) counter = len(fs) def _on_completion(f): nonlocal counter counter -= 1 if (counter <= 0 or return_when == FIRST_COMPLETED or return_when == FIRST_EXCEPTION and (not f.cancelled() and f.exception() is not None)): if timeout_handle is not None: timeout_handle.cancel() if not waiter.done(): waiter.set_result(None) for f in fs: f.add_done_callback(_on_completion) try: await waiter finally: if timeout_handle is not None: timeout_handle.cancel() done, pending = set(), set() for f in fs: f.remove_done_callback(_on_completion) if f.done(): done.add(f) else: pending.add(f) return done, pending async def _cancel_and_wait(fut, loop): """Cancel the *fut* future or task and wait until it completes.""" waiter = loop.create_future() cb = functools.partial(_release_waiter, waiter) fut.add_done_callback(cb) try: fut.cancel() # We cannot wait on *fut* directly to make # sure _cancel_and_wait itself is reliably cancellable. await waiter finally: fut.remove_done_callback(cb) # This is *not* a @coroutine! It is just an iterator (yielding Futures). def as_completed(fs, *, loop=None, timeout=None): """Return an iterator whose values are coroutines. When waiting for the yielded coroutines you'll get the results (or exceptions!) of the original Futures (or coroutines), in the order in which and as soon as they complete. This differs from PEP 3148; the proper way to use this is: for f in as_completed(fs): result = await f # The 'await' may raise. # Use result. If a timeout is specified, the 'await' will raise TimeoutError when the timeout occurs before all Futures are done. Note: The futures 'f' are not necessarily members of fs. """ if futures.isfuture(fs) or coroutines.iscoroutine(fs): raise TypeError(f"expect a list of futures, not {type(fs).__name__}") loop = loop if loop is not None else events.get_event_loop() todo = {ensure_future(f, loop=loop) for f in set(fs)} from .queues import Queue # Import here to avoid circular import problem. done = Queue(loop=loop) timeout_handle = None def _on_timeout(): for f in todo: f.remove_done_callback(_on_completion) done.put_nowait(None) # Queue a dummy value for _wait_for_one(). todo.clear() # Can't do todo.remove(f) in the loop. def _on_completion(f): if not todo: return # _on_timeout() was here first. todo.remove(f) done.put_nowait(f) if not todo and timeout_handle is not None: timeout_handle.cancel() async def _wait_for_one(): f = await done.get() if f is None: # Dummy value from _on_timeout(). raise futures.TimeoutError return f.result() # May raise f.exception(). for f in todo: f.add_done_callback(_on_completion) if todo and timeout is not None: timeout_handle = loop.call_later(timeout, _on_timeout) for _ in range(len(todo)): yield _wait_for_one() @types.coroutine def __sleep0(): """Skip one event loop run cycle. This is a private helper for 'asyncio.sleep()', used when the 'delay' is set to 0. It uses a bare 'yield' expression (which Task.__step knows how to handle) instead of creating a Future object. """ yield async def sleep(delay, result=None, *, loop=None): """Coroutine that completes after a given time (in seconds).""" if delay <= 0: await __sleep0() return result if loop is None: loop = events.get_event_loop() future = loop.create_future() h = loop.call_later(delay, futures._set_result_unless_cancelled, future, result) try: return await future finally: h.cancel() def ensure_future(coro_or_future, *, loop=None): """Wrap a coroutine or an awaitable in a future. If the argument is a Future, it is returned directly. """ if coroutines.iscoroutine(coro_or_future): if loop is None: loop = events.get_event_loop() task = loop.create_task(coro_or_future) if task._source_traceback: del task._source_traceback[-1] return task elif futures.isfuture(coro_or_future): if loop is not None and loop is not futures._get_loop(coro_or_future): raise ValueError('loop argument must agree with Future') return coro_or_future elif inspect.isawaitable(coro_or_future): return ensure_future(_wrap_awaitable(coro_or_future), loop=loop) else: raise TypeError('An asyncio.Future, a coroutine or an awaitable is ' 'required') @coroutine def _wrap_awaitable(awaitable): """Helper for asyncio.ensure_future(). Wraps awaitable (an object with __await__) into a coroutine that will later be wrapped in a Task by ensure_future(). """ return (yield from awaitable.__await__()) class _GatheringFuture(futures.Future): """Helper for gather(). This overrides cancel() to cancel all the children and act more like Task.cancel(), which doesn't immediately mark itself as cancelled. """ def __init__(self, children, *, loop=None): super().__init__(loop=loop) self._children = children self._cancel_requested = False def cancel(self): if self.done(): return False ret = False for child in self._children: if child.cancel(): ret = True if ret: # If any child tasks were actually cancelled, we should # propagate the cancellation request regardless of # *return_exceptions* argument. See issue 32684. self._cancel_requested = True return ret def gather(*coros_or_futures, loop=None, return_exceptions=False): """Return a future aggregating results from the given coroutines/futures. Coroutines will be wrapped in a future and scheduled in the event loop. They will not necessarily be scheduled in the same order as passed in. All futures must share the same event loop. If all the tasks are done successfully, the returned future's result is the list of results (in the order of the original sequence, not necessarily the order of results arrival). If *return_exceptions* is True, exceptions in the tasks are treated the same as successful results, and gathered in the result list; otherwise, the first raised exception will be immediately propagated to the returned future. Cancellation: if the outer Future is cancelled, all children (that have not completed yet) are also cancelled. If any child is cancelled, this is treated as if it raised CancelledError -- the outer Future is *not* cancelled in this case. (This is to prevent the cancellation of one child to cause other children to be cancelled.) """ if not coros_or_futures: if loop is None: loop = events.get_event_loop() outer = loop.create_future() outer.set_result([]) return outer def _done_callback(fut): nonlocal nfinished nfinished += 1 if outer.done(): if not fut.cancelled(): # Mark exception retrieved. fut.exception() return if not return_exceptions: if fut.cancelled(): # Check if 'fut' is cancelled first, as # 'fut.exception()' will *raise* a CancelledError # instead of returning it. exc = futures.CancelledError() outer.set_exception(exc) return else: exc = fut.exception() if exc is not None: outer.set_exception(exc) return if nfinished == nfuts: # All futures are done; create a list of results # and set it to the 'outer' future. results = [] for fut in children: if fut.cancelled(): # Check if 'fut' is cancelled first, as # 'fut.exception()' will *raise* a CancelledError # instead of returning it. res = futures.CancelledError() else: res = fut.exception() if res is None: res = fut.result() results.append(res) if outer._cancel_requested: # If gather is being cancelled we must propagate the # cancellation regardless of *return_exceptions* argument. # See issue 32684. outer.set_exception(futures.CancelledError()) else: outer.set_result(results) arg_to_fut = {} children = [] nfuts = 0 nfinished = 0 for arg in coros_or_futures: if arg not in arg_to_fut: fut = ensure_future(arg, loop=loop) if loop is None: loop = futures._get_loop(fut) if fut is not arg: # 'arg' was not a Future, therefore, 'fut' is a new # Future created specifically for 'arg'. Since the caller # can't control it, disable the "destroy pending task" # warning. fut._log_destroy_pending = False nfuts += 1 arg_to_fut[arg] = fut fut.add_done_callback(_done_callback) else: # There's a duplicate Future object in coros_or_futures. fut = arg_to_fut[arg] children.append(fut) outer = _GatheringFuture(children, loop=loop) return outer def shield(arg, *, loop=None): """Wait for a future, shielding it from cancellation. The statement res = await shield(something()) is exactly equivalent to the statement res = await something() *except* that if the coroutine containing it is cancelled, the task running in something() is not cancelled. From the POV of something(), the cancellation did not happen. But its caller is still cancelled, so the yield-from expression still raises CancelledError. Note: If something() is cancelled by other means this will still cancel shield(). If you want to completely ignore cancellation (not recommended) you can combine shield() with a try/except clause, as follows: try: res = await shield(something()) except CancelledError: res = None """ inner = ensure_future(arg, loop=loop) if inner.done(): # Shortcut. return inner loop = futures._get_loop(inner) outer = loop.create_future() def _done_callback(inner): if outer.cancelled(): if not inner.cancelled(): # Mark inner's result as retrieved. inner.exception() return if inner.cancelled(): outer.cancel() else: exc = inner.exception() if exc is not None: outer.set_exception(exc) else: outer.set_result(inner.result()) inner.add_done_callback(_done_callback) return outer def run_coroutine_threadsafe(coro, loop): """Submit a coroutine object to a given event loop. Return a concurrent.futures.Future to access the result. """ if not coroutines.iscoroutine(coro): raise TypeError('A coroutine object is required') future = concurrent.futures.Future() def callback(): try: futures._chain_future(ensure_future(coro, loop=loop), future) except Exception as exc: if future.set_running_or_notify_cancel(): future.set_exception(exc) raise loop.call_soon_threadsafe(callback) return future # WeakSet containing all alive tasks. _all_tasks = weakref.WeakSet() # Dictionary containing tasks that are currently active in # all running event loops. {EventLoop: Task} _current_tasks = {} def _register_task(task): """Register a new task in asyncio as executed by loop.""" _all_tasks.add(task) def _enter_task(loop, task): current_task = _current_tasks.get(loop) if current_task is not None: raise RuntimeError(f"Cannot enter into task {task!r} while another " f"task {current_task!r} is being executed.") _current_tasks[loop] = task def _leave_task(loop, task): current_task = _current_tasks.get(loop) if current_task is not task: raise RuntimeError(f"Leaving task {task!r} does not match " f"the current task {current_task!r}.") del _current_tasks[loop] def _unregister_task(task): """Unregister a task.""" _all_tasks.discard(task) _py_register_task = _register_task _py_unregister_task = _unregister_task _py_enter_task = _enter_task _py_leave_task = _leave_task try: from _asyncio import (_register_task, _unregister_task, _enter_task, _leave_task, _all_tasks, _current_tasks) except ImportError: pass else: _c_register_task = _register_task _c_unregister_task = _unregister_task _c_enter_task = _enter_task _c_leave_task = _leave_task