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_running_loop()
else:
warnings.warn("The loop argument is deprecated since Python 3.8, "
"and scheduled for removal in Python 3.10.",
DeprecationWarning, stacklevel=2)
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 exceptions.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 exceptions.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 https://bugs.python.org/issue32751
await _cancel_and_wait(fut, loop=loop)
raise exceptions.TimeoutError()
finally:
timeout_handle.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 _ASYNC_LAZY_VALUE_TYPE is not None and type(coro_or_future) is _ASYNC_LAZY_VALUE_TYPE:
return coro_or_future.ensure_future(loop)
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('The future belongs to a different loop than '
'the one specified as the loop argument')
return coro_or_future
elif _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 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__}")
from .queues import Queue # Import here to avoid circular import problem.
done = Queue(loop=loop)
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)
todo = {ensure_future(f, loop=loop) for f in set(fs)}
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 exceptions.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()
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_running_loop()
else:
warnings.warn("The loop argument is deprecated since Python 3.8, "
"and scheduled for removal in Python 3.10.",
DeprecationWarning, stacklevel=2)
fs = {ensure_future(f, loop=loop) for f in set(fs)}
return await _wait(fs, timeout, return_when, loop)
def callback():
try:
futures._chain_future(ensure_future(coro, loop=loop), future)
except (SystemExit, KeyboardInterrupt):
raise
except BaseException as exc:
if future.set_running_or_notify_cancel():
future.set_exception(exc)
raise
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, 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 *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:
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
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_running_loop()
else:
warnings.warn(
"The loop argument is deprecated since Python 3.8, "
"and scheduled for removal in Python 3.10.",
DeprecationWarning,
stacklevel=2)
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 exceptions.TimeoutError()
fut = ensure_future(fut, loop=loop)
waiter = _asyncio._AwaitingFuture(fut, loop=loop)
timed_out = False
def on_timeout(waiter, *args):
nonlocal timed_out
timed_out = True
waiter.cancel()
timeout_handle = loop.call_later(timeout, on_timeout, waiter)
try:
# wait until the future completes or the timeout
try:
await waiter
except exceptions.CancelledError:
if fut.done():
# The future may have completed in the same trip of the event
# loop as the timeout occurring.
return fut.result()
if timed_out:
# We must ensure that the task is not running
# after wait_for() returns.
# See https://bugs.python.org/issue32751
await _cancel_and_wait(fut, loop=loop)
raise exceptions.TimeoutError()
fut.cancel()
raise
return fut.result()
finally:
timeout_handle.cancel()