def multi_future(children, quiet_exceptions=()):
"""Wait for multiple asynchronous futures in parallel.
This function is similar to `multi`, but does not support
`YieldPoints <YieldPoint>`.
.. versionadded:: 4.0
.. versionchanged:: 4.2
If multiple ``Futures`` fail, any exceptions after the first (which is
raised) will be logged. Added the ``quiet_exceptions``
argument to suppress this logging for selected exception types.
.. deprecated:: 4.3
Use `multi` instead.
"""
if isinstance(children, dict):
keys = list(children.keys())
children = children.values()
else:
keys = None
children = list(map(convert_yielded, children))
assert all(is_future(i) for i in children)
unfinished_children = set(children)
future = Future()
if not children:
future.set_result({} if keys is not None else [])
def callback(f):
unfinished_children.remove(f)
if not unfinished_children:
result_list = []
for f in children:
try:
result_list.append(f.result())
except Exception as e:
if future.done():
if not isinstance(e, quiet_exceptions):
app_log.error("Multiple exceptions in yield list",
exc_info=True)
else:
future.set_exc_info(sys.exc_info())
if not future.done():
if keys is not None:
future.set_result(dict(zip(keys, result_list)))
else:
future.set_result(result_list)
listening = set()
for f in children:
if f not in listening:
listening.add(f)
f.add_done_callback(callback)
return future
def Task(func, *args, **kwargs):
"""Adapts a callback-based asynchronous function for use in coroutines.
Takes a function (and optional additional arguments) and runs it with
those arguments plus a ``callback`` keyword argument. The argument passed
to the callback is returned as the result of the yield expression.
.. versionchanged:: 4.0
``gen.Task`` is now a function that returns a `.Future`, instead of
a subclass of `YieldPoint`. It still behaves the same way when
yielded.
"""
future = Future()
def handle_exception(typ, value, tb):
if future.done():
return False
future.set_exc_info((typ, value, tb))
return True
def set_result(result):
if future.done():
return
future.set_result(result)
with stack_context.ExceptionStackContext(handle_exception):
func(*args, callback=_argument_adapter(set_result), **kwargs)
return future
def wait_for_exit(self, raise_error=True):
"""Returns a `.Future` which resolves when the process exits.
Usage::
ret = yield proc.wait_for_exit()
This is a coroutine-friendly alternative to `set_exit_callback`
(and a replacement for the blocking `subprocess.Popen.wait`).
By default, raises `subprocess.CalledProcessError` if the process
has a non-zero exit status. Use ``wait_for_exit(raise_error=False)``
to suppress this behavior and return the exit status without raising.
.. versionadded:: 4.2
"""
future = Future()
def callback(ret):
if ret != 0 and raise_error:
# Unfortunately we don't have the original args any more.
future.set_exception(CalledProcessError(ret, None))
else:
future.set_result(ret)
self.set_exit_callback(callback)
return future
def sleep(duration):
"""Return a `.Future` that resolves after the given number of seconds.
When used with ``yield`` in a coroutine, this is a non-blocking
analogue to `time.sleep` (which should not be used in coroutines
because it is blocking)::
yield gen.sleep(0.5)
Note that calling this function on its own does nothing; you must
wait on the `.Future` it returns (usually by yielding it).
.. versionadded:: 4.1
"""
f = Future()
IOLoop.current().call_later(duration, lambda: f.set_result(None))
return f
def maybe_future(x):
"""Converts ``x`` into a `.Future`.
If ``x`` is already a `.Future`, it is simply returned; otherwise
it is wrapped in a new `.Future`. This is suitable for use as
``result = yield gen.maybe_future(f())`` when you don't know whether
``f()`` returns a `.Future` or not.
.. deprecated:: 4.3
This function only handles ``Futures``, not other yieldable objects.
Instead of `maybe_future`, check for the non-future result types
you expect (often just ``None``), and ``yield`` anything unknown.
"""
if is_future(x):
return x
else:
fut = Future()
fut.set_result(x)
return fut
def with_timeout(timeout, future, io_loop=None, quiet_exceptions=()):
"""Wraps a `.Future` (or other yieldable object) in a timeout.
Raises `TimeoutError` if the input future does not complete before
``timeout``, which may be specified in any form allowed by
`.IOLoop.add_timeout` (i.e. a `datetime.timedelta` or an absolute time
relative to `.IOLoop.time`)
If the wrapped `.Future` fails after it has timed out, the exception
will be logged unless it is of a type contained in ``quiet_exceptions``
(which may be an exception type or a sequence of types).
Does not support `YieldPoint` subclasses.
.. versionadded:: 4.0
.. versionchanged:: 4.1
Added the ``quiet_exceptions`` argument and the logging of unhandled
exceptions.
.. versionchanged:: 4.4
Added support for yieldable objects other than `.Future`.
"""
# TODO: allow YieldPoints in addition to other yieldables?
# Tricky to do with stack_context semantics.
#
# It's tempting to optimize this by cancelling the input future on timeout
# instead of creating a new one, but A) we can't know if we are the only
# one waiting on the input future, so cancelling it might disrupt other
# callers and B) concurrent futures can only be cancelled while they are
# in the queue, so cancellation cannot reliably bound our waiting time.
future = convert_yielded(future)
result = Future()
chain_future(future, result)
if io_loop is None:
io_loop = IOLoop.current()
def error_callback(future):
try:
future.result()
except Exception as e:
if not isinstance(e, quiet_exceptions):
app_log.error("Exception in Future %r after timeout",
future,
exc_info=True)
def timeout_callback():
result.set_exception(TimeoutError("Timeout"))
# In case the wrapped future goes on to fail, log it.
future.add_done_callback(error_callback)
timeout_handle = io_loop.add_timeout(timeout, timeout_callback)
if isinstance(future, Future):
# We know this future will resolve on the IOLoop, so we don't
# need the extra thread-safety of IOLoop.add_future (and we also
# don't care about StackContext here.
future.add_done_callback(
lambda future: io_loop.remove_timeout(timeout_handle))
else:
# concurrent.futures.Futures may resolve on any thread, so we
# need to route them back to the IOLoop.
io_loop.add_future(
future, lambda future: io_loop.remove_timeout(timeout_handle))
return result
analogue to `time.sleep` (which should not be used in coroutines
because it is blocking)::
yield gen.sleep(0.5)
Note that calling this function on its own does nothing; you must
wait on the `.Future` it returns (usually by yielding it).
.. versionadded:: 4.1
"""
f = Future()
IOLoop.current().call_later(duration, lambda: f.set_result(None))
return f
_null_future = Future()
_null_future.set_result(None)
moment = Future()
moment.__doc__ = \
"""A special object which may be yielded to allow the IOLoop to run for
one iteration.
This is not needed in normal use but it can be helpful in long-running
coroutines that are likely to yield Futures that are ready instantly.
Usage: ``yield gen.moment``
.. versionadded:: 4.0
"""
moment.set_result(None)