"""A Future class similar to the one in PEP 3148.""" __all__ = ['CancelledError', 'TimeoutError', 'InvalidStateError', 'Future', 'wrap_future', 'isfuture'] import concurrent.futures import logging import sys import traceback from . import base_futures from . import compat from . import events CancelledError = base_futures.CancelledError InvalidStateError = base_futures.InvalidStateError TimeoutError = base_futures.TimeoutError isfuture = base_futures.isfuture _PENDING = base_futures._PENDING _CANCELLED = base_futures._CANCELLED _FINISHED = base_futures._FINISHED STACK_DEBUG = logging.DEBUG - 1 # heavy-duty debugging class Future: """This class is *almost* compatible with concurrent.futures.Future. Differences: - result() and exception() do not take a timeout argument and raise an exception when the future isn't done yet. - Callbacks registered with add_done_callback() are always called via the event loop's call_soon_threadsafe(). - This class is not compatible with the wait() and as_completed() methods in the concurrent.futures package. (In Python 3.4 or later we may be able to unify the implementations.) """ # Class variables serving as defaults for instance variables. _state = _PENDING _result = None _exception = None _loop = None _source_traceback = None # This field is used for a dual purpose: # - Its presence is a marker to declare that a class implements # the Future protocol (i.e. is intended to be duck-type compatible). # The value must also be not-None, to enable a subclass to declare # that it is not compatible by setting this to None. # - It is set by __iter__() below so that Task._step() can tell # the difference between `yield from Future()` (correct) vs. # `yield Future()` (incorrect). _asyncio_future_blocking = False _log_traceback = False # Used for Python 3.4 and later _tb_logger = None # Used for Python 3.3 only def __init__(self, *, loop=None): """Initialize the future. The optional event_loop argument allows explicitly setting the event loop object used by the future. If it's not provided, the future uses the default event loop. """ if loop is None: self._loop = events.get_event_loop() else: self._loop = loop self._callbacks = [] if self._loop.get_debug(): self._source_traceback = traceback.extract_stack(sys._getframe(1)) _repr_info = base_futures._future_repr_info def __repr__(self): return '<%s %s>' % (self.__class__.__name__, ' '.join(self._repr_info())) def __del__(self): if not self._log_traceback: # set_exception() was not called, or result() or exception() # has consumed the exception return exc = self._exception context = { 'message': ('%s exception was never retrieved' % self.__class__.__name__), 'exception': exc, 'future': self, } if self._source_traceback: context['source_traceback'] = self._source_traceback self._loop.call_exception_handler(context) def cancel(self): """Cancel the future and schedule callbacks. If the future is already done or cancelled, return False. Otherwise, change the future's state to cancelled, schedule the callbacks and return True. """ self._log_traceback = False if self._state != _PENDING: return False self._state = _CANCELLED self._schedule_callbacks() return True def _schedule_callbacks(self): """Internal: Ask the event loop to call all callbacks. The callbacks are scheduled to be called as soon as possible. Also clears the callback list. """ callbacks = self._callbacks[:] if not callbacks: return self._callbacks[:] = [] for callback in callbacks: self._loop.call_soon(callback, self) def cancelled(self): """Return True if the future was cancelled.""" return self._state == _CANCELLED # Don't implement running(); see http://bugs.python.org/issue18699 def done(self): """Return True if the future is done. Done means either that a result / exception are available, or that the future was cancelled. """ return self._state != _PENDING def result(self): """Return the result this future represents. If the future has been cancelled, raises CancelledError. If the future's result isn't yet available, raises InvalidStateError. If the future is done and has an exception set, this exception is raised. """ if self._state == _CANCELLED: raise CancelledError if self._state != _FINISHED: raise InvalidStateError('Result is not ready.') self._log_traceback = False if self._tb_logger is not None: self._tb_logger.clear() self._tb_logger = None if self._exception is not None: raise self._exception return self._result def exception(self): """Return the exception that was set on this future. The exception (or None if no exception was set) is returned only if the future is done. If the future has been cancelled, raises CancelledError. If the future isn't done yet, raises InvalidStateError. """ if self._state == _CANCELLED: raise CancelledError if self._state != _FINISHED: raise InvalidStateError('Exception is not set.') self._log_traceback = False if self._tb_logger is not None: self._tb_logger.clear() self._tb_logger = None return self._exception def add_done_callback(self, fn): """Add a callback to be run when the future becomes done. The callback is called with a single argument - the future object. If the future is already done when this is called, the callback is scheduled with call_soon. """ if self._state != _PENDING: self._loop.call_soon(fn, self) else: self._callbacks.append(fn) # New method not in PEP 3148. def remove_done_callback(self, fn): """Remove all instances of a callback from the "call when done" list. Returns the number of callbacks removed. """ filtered_callbacks = [f for f in self._callbacks if f != fn] removed_count = len(self._callbacks) - len(filtered_callbacks) if removed_count: self._callbacks[:] = filtered_callbacks return removed_count # So-called internal methods (note: no set_running_or_notify_cancel()). def set_result(self, result): """Mark the future done and set its result. If the future is already done when this method is called, raises InvalidStateError. """ if self._state != _PENDING: raise InvalidStateError('{}: {!r}'.format(self._state, self)) self._result = result self._state = _FINISHED self._schedule_callbacks() def set_exception(self, exception): """Mark the future done and set an exception. If the future is already done when this method is called, raises InvalidStateError. """ if self._state != _PENDING: raise InvalidStateError('{}: {!r}'.format(self._state, self)) if isinstance(exception, type): exception = exception() if type(exception) is StopIteration: raise TypeError("StopIteration interacts badly with generators " "and cannot be raised into a Future") self._exception = exception self._state = _FINISHED self._schedule_callbacks() self._log_traceback = True def __iter__(self): if not self.done(): self._asyncio_future_blocking = True yield self # This tells Task to wait for completion. assert self.done(), "yield from wasn't used with future" return self.result() # May raise too. if compat.PY35: __await__ = __iter__ # make compatible with 'await' expression # Needed for testing purposes. _PyFuture = Future def _set_result_unless_cancelled(fut, result): """Helper setting the result only if the future was not cancelled.""" if fut.cancelled(): return fut.set_result(result) def _set_concurrent_future_state(concurrent, source): """Copy state from a future to a concurrent.futures.Future.""" assert source.done() if source.cancelled(): concurrent.cancel() if not concurrent.set_running_or_notify_cancel(): return exception = source.exception() if exception is not None: concurrent.set_exception(exception) else: result = source.result() concurrent.set_result(result) def _copy_future_state(source, dest): """Internal helper to copy state from another Future. The other Future may be a concurrent.futures.Future. """ assert source.done() if dest.cancelled(): return assert not dest.done() if source.cancelled(): dest.cancel() else: exception = source.exception() if exception is not None: dest.set_exception(exception) else: result = source.result() dest.set_result(result) def _chain_future(source, destination): """Chain two futures so that when one completes, so does the other. The result (or exception) of source will be copied to destination. If destination is cancelled, source gets cancelled too. Compatible with both asyncio.Future and concurrent.futures.Future. """ if not isfuture(source) and not isinstance(source, concurrent.futures.Future): raise TypeError('A future is required for source argument') if not isfuture(destination) and not isinstance(destination, concurrent.futures.Future): raise TypeError('A future is required for destination argument') source_loop = source._loop if isfuture(source) else None dest_loop = destination._loop if isfuture(destination) else None def _set_state(future, other): if isfuture(future): _copy_future_state(other, future) else: _set_concurrent_future_state(future, other) def _call_check_cancel(destination): if destination.cancelled(): if source_loop is None or source_loop is dest_loop: source.cancel() else: source_loop.call_soon_threadsafe(source.cancel) def _call_set_state(source): if dest_loop is None or dest_loop is source_loop: _set_state(destination, source) else: dest_loop.call_soon_threadsafe(_set_state, destination, source) destination.add_done_callback(_call_check_cancel) source.add_done_callback(_call_set_state) def wrap_future(future, *, loop=None): """Wrap concurrent.futures.Future object.""" if isfuture(future): return future assert isinstance(future, concurrent.futures.Future), \ 'concurrent.futures.Future is expected, got {!r}'.format(future) if loop is None: loop = events.get_event_loop() new_future = loop.create_future() _chain_future(future, new_future) return new_future try: import _asyncio except ImportError: pass else: # _CFuture is needed for tests. Future = _CFuture = _asyncio.Future