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()
return {t for t in _all_tasks if futures._get_loop(t) is 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 https://bugs.python.org/issue34970 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 https://bugs.python.org/issue34970 bug
return {t for t in list(_all_tasks) if futures._get_loop(t) is loop}
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 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')
def all_tasks(loop=None):
"""Return a set of all tasks for the loop."""
if loop is None:
loop = events.get_running_loop()
return {t for t in _all_tasks
if futures._get_loop(t) is loop and not t.done()}
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
"""
if loop is not None:
warnings.warn(
"The loop argument is deprecated since Python 3.8, "
"and scheduled for removal in Python 3.10.",
DeprecationWarning,
stacklevel=2)
inner = ensure_future(arg, loop=loop)
if inner.done():
# Shortcut.
return inner
loop = futures._get_loop(inner)
outer = loop.create_future()
def _inner_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())
def _outer_done_callback(outer):
if not inner.done():
inner.remove_done_callback(_inner_done_callback)
inner.add_done_callback(_inner_done_callback)
outer.add_done_callback(_outer_done_callback)
return outer
def gather(*coros_or_futures, 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 *return_exceptions* is False, cancelling gather() after it
has been marked done won't cancel any submitted awaitables.
For instance, gather can be marked done after propagating an
exception to the caller, therefore, calling ``gather.cancel()``
after catching an exception (raised by one of the awaitables) from
gather won't cancel any other awaitables.
"""
if not coros_or_futures:
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 = fut._make_cancelled_error()
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.
# Also, since we're adding the exception return value
# to 'results' instead of raising it, don't bother
# setting __context__. This also lets us preserve
# calling '_make_cancelled_error()' at most once.
res = exceptions.CancelledError(
'' if fut._cancel_message is None else fut.
_cancel_message)
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.
exc = fut._make_cancelled_error()
outer.set_exception(exc)
else:
outer.set_result(results)
arg_to_fut = {}
children = []
nfuts = 0
nfinished = 0
loop = None
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 _gather(*coros_or_futures, loop=None, return_exceptions=False):
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 is None or 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 = fut._make_cancelled_error()
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.
# Also, since we're adding the exception return value
# to 'results' instead of raising it, don't bother
# setting __context__. This also lets us preserve
# calling '_make_cancelled_error()' at most once.
res = exceptions.CancelledError(
'' if fut._cancel_message is None else
fut._cancel_message)
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.
exc = fut._make_cancelled_error()
outer.set_exception(exc)
else:
outer.set_result(results)
arg_to_fut = {}
children = []
nfuts = 0
nfinished = 0
outer = None # bpo-46672
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 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 _check_future(self, future):
"""Return False if task and future loops are not compatible."""
return futures._get_loop(future) is self._loop
def all_tasks(loop=None):
"""Return a set of all tasks for the loop."""
if loop is None:
loop = events.get_running_loop()
return {t for t in _all_tasks
if futures._get_loop(t) is loop and not t.done()}
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).
try:
if exc is None:
# We use the `send` method directly, because coroutines
# don't have `__iter__` and `__next__` methods.
result = coro.send(None)
else:
result = coro.throw(exc)
except StopIteration as exc:
if self._must_cancel:
# Task is cancelled right before coro stops.
self._must_cancel = False
super().set_exception(futures.CancelledError())
else:
super().set_result(exc.value)
except futures.CancelledError:
super().cancel() # I.e., Future.cancel(self).
except Exception as exc:
super().set_exception(exc)
except BaseException as exc:
super().set_exception(exc)
raise
else:
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._loop.call_soon(
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._loop.call_soon(
self.__step, new_exc, context=self._context)
else:
result._asyncio_future_blocking = False
result.add_done_callback(
self.__wakeup, context=self._context)
self._fut_waiter = result
if self._must_cancel:
if self._fut_waiter.cancel():
self._must_cancel = False
else:
new_exc = RuntimeError(
f'yield was used instead of yield from '
f'in task {self!r} with {result!r}')
self._loop.call_soon(
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._loop.call_soon(
self.__step, new_exc, context=self._context)
else:
# Yielding something else is an error.
new_exc = RuntimeError(f'Task got bad yield: {result!r}')
self._loop.call_soon(
self.__step, new_exc, context=self._context)
finally:
_leave_task(self._loop, self)
self = None # Needed to break cycles when an exception occurs.
def all_tasks(loop=None):
"""Return a set of all tasks for the loop."""
if loop is None:
loop = events.get_event_loop()
return {t for t in _all_tasks if futures._get_loop(t) is loop}
def all_tasks(loop=None):
"""Return a set of all tasks for the loop."""
if loop is None:
loop = events.get_event_loop()
return {t for t in _all_tasks if futures._get_loop(t) is loop}
def __step(self, exc=None):
if self.done():
raise exceptions.InvalidStateError(
f'_step(): already done: {self!r}, {exc!r}')
if self._must_cancel:
if not isinstance(exc, exceptions.CancelledError):
exc = exceptions.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).
try:
if exc is None:
# We use the `send` method directly, because coroutines
# don't have `__iter__` and `__next__` methods.
result = coro.send(None)
else:
result = coro.throw(exc)
except StopIteration as exc:
if self._must_cancel:
# Task is cancelled right before coro stops.
self._must_cancel = False
super().set_exception(exceptions.CancelledError())
else:
super().set_result(exc.value)
except exceptions.CancelledError:
super().cancel() # I.e., Future.cancel(self).
except (KeyboardInterrupt, SystemExit) as exc:
super().set_exception(exc)
raise
except BaseException as exc:
super().set_exception(exc)
else:
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._loop.call_soon(
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._loop.call_soon(
self.__step, new_exc, context=self._context)
else:
result._asyncio_future_blocking = False
result.add_done_callback(
self.__wakeup, context=self._context)
self._fut_waiter = result
if self._must_cancel:
if self._fut_waiter.cancel():
self._must_cancel = False
else:
new_exc = RuntimeError(
f'yield was used instead of yield from '
f'in task {self!r} with {result!r}')
self._loop.call_soon(
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._loop.call_soon(
self.__step, new_exc, context=self._context)
else:
# Yielding something else is an error.
new_exc = RuntimeError(f'Task got bad yield: {result!r}')
self._loop.call_soon(
self.__step, new_exc, context=self._context)
finally:
_leave_task(self._loop, self)
self = None # Needed to break cycles when an exception occurs.
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()
else:
warnings.warn("The loop argument is deprecated since Python 3.8, "
"and scheduled for removal in Python 3.10.",
DeprecationWarning, stacklevel=2)
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 = exceptions.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 = exceptions.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(exceptions.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 gather(*coros_or_futures, loop=None, return_exceptions=False):
"""
给 协程/futures 返回一个future聚合结果
Return a future aggregating results from the given coroutines/futures.
协程会包裹 futures 对象，并安排在事件循环中。它们不一定按照传入的顺序排列
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.
所有期货必须共享相同的事件循环。All futures must share the same event loop.
如果所有任务都成功完成，则返回的future的结果是结果列表（按原始序列的顺序，不一定是结果到达的顺序）
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).
如果* return_exceptions *为True，则任务中的异常将被视为与成功结果相同，并在结果列表中收集;
If *return_exceptions* is True,exceptions in the tasks are treated the same as successful results, and gathered in the result list;
否则，第一个引发的异常将立即传播到返回的future中。otherwise, the first raised exception will be immediately propagated to the returned future.
取消：如果外部 Future 被取消，所有尚未完成的子任务也将被取消。
Cancellation: if the outer Future is cancelled, all children (that have not completed yet) are also cancelled.
如果任何子项被取消，则将其视为已引发CancelledError - 在这种情况下，外部Future未被取消。（这是为了防止一个子任务被取消导致其他子任务的取消）
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