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0360e9f346
After a long deliberation we ended up feeling that the message argument for Future.cancel(), added in 3.9, was a bad idea, so we're deprecating it in 3.11 and plan to remove it in 3.13.
431 lines
14 KiB
Python
431 lines
14 KiB
Python
"""A Future class similar to the one in PEP 3148."""
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__all__ = (
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'Future', 'wrap_future', 'isfuture',
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)
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import concurrent.futures
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import contextvars
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import logging
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import sys
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import warnings
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from types import GenericAlias
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from . import base_futures
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from . import events
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from . import exceptions
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from . import format_helpers
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isfuture = base_futures.isfuture
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_PENDING = base_futures._PENDING
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_CANCELLED = base_futures._CANCELLED
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_FINISHED = base_futures._FINISHED
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STACK_DEBUG = logging.DEBUG - 1 # heavy-duty debugging
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class Future:
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"""This class is *almost* compatible with concurrent.futures.Future.
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Differences:
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- This class is not thread-safe.
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- result() and exception() do not take a timeout argument and
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raise an exception when the future isn't done yet.
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- Callbacks registered with add_done_callback() are always called
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via the event loop's call_soon().
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- This class is not compatible with the wait() and as_completed()
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methods in the concurrent.futures package.
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(In Python 3.4 or later we may be able to unify the implementations.)
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"""
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# Class variables serving as defaults for instance variables.
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_state = _PENDING
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_result = None
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_exception = None
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_loop = None
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_source_traceback = None
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_cancel_message = None
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# A saved CancelledError for later chaining as an exception context.
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_cancelled_exc = None
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# This field is used for a dual purpose:
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# - Its presence is a marker to declare that a class implements
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# the Future protocol (i.e. is intended to be duck-type compatible).
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# The value must also be not-None, to enable a subclass to declare
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# that it is not compatible by setting this to None.
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# - It is set by __iter__() below so that Task._step() can tell
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# the difference between
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# `await Future()` or`yield from Future()` (correct) vs.
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# `yield Future()` (incorrect).
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_asyncio_future_blocking = False
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__log_traceback = False
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def __init__(self, *, loop=None):
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"""Initialize the future.
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The optional event_loop argument allows explicitly setting the event
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loop object used by the future. If it's not provided, the future uses
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the default event loop.
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"""
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if loop is None:
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self._loop = events._get_event_loop()
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else:
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self._loop = loop
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self._callbacks = []
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if self._loop.get_debug():
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self._source_traceback = format_helpers.extract_stack(
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sys._getframe(1))
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def __repr__(self):
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return base_futures._future_repr(self)
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def __del__(self):
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if not self.__log_traceback:
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# set_exception() was not called, or result() or exception()
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# has consumed the exception
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return
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exc = self._exception
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context = {
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'message':
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f'{self.__class__.__name__} exception was never retrieved',
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'exception': exc,
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'future': self,
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}
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if self._source_traceback:
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context['source_traceback'] = self._source_traceback
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self._loop.call_exception_handler(context)
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__class_getitem__ = classmethod(GenericAlias)
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@property
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def _log_traceback(self):
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return self.__log_traceback
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@_log_traceback.setter
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def _log_traceback(self, val):
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if val:
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raise ValueError('_log_traceback can only be set to False')
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self.__log_traceback = False
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def get_loop(self):
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"""Return the event loop the Future is bound to."""
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loop = self._loop
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if loop is None:
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raise RuntimeError("Future object is not initialized.")
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return loop
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def _make_cancelled_error(self):
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"""Create the CancelledError to raise if the Future is cancelled.
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This should only be called once when handling a cancellation since
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it erases the saved context exception value.
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"""
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if self._cancelled_exc is not None:
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exc = self._cancelled_exc
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self._cancelled_exc = None
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return exc
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if self._cancel_message is None:
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exc = exceptions.CancelledError()
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else:
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exc = exceptions.CancelledError(self._cancel_message)
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exc.__context__ = self._cancelled_exc
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# Remove the reference since we don't need this anymore.
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self._cancelled_exc = None
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return exc
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def cancel(self, msg=None):
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"""Cancel the future and schedule callbacks.
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If the future is already done or cancelled, return False. Otherwise,
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change the future's state to cancelled, schedule the callbacks and
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return True.
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"""
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if msg is not None:
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warnings.warn("Passing 'msg' argument to Future.cancel() "
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"is deprecated since Python 3.11, and "
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"scheduled for removal in Python 3.14.",
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DeprecationWarning, stacklevel=2)
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self.__log_traceback = False
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if self._state != _PENDING:
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return False
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self._state = _CANCELLED
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self._cancel_message = msg
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self.__schedule_callbacks()
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return True
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def __schedule_callbacks(self):
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"""Internal: Ask the event loop to call all callbacks.
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The callbacks are scheduled to be called as soon as possible. Also
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clears the callback list.
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"""
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callbacks = self._callbacks[:]
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if not callbacks:
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return
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self._callbacks[:] = []
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for callback, ctx in callbacks:
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self._loop.call_soon(callback, self, context=ctx)
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def cancelled(self):
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"""Return True if the future was cancelled."""
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return self._state == _CANCELLED
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# Don't implement running(); see http://bugs.python.org/issue18699
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def done(self):
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"""Return True if the future is done.
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Done means either that a result / exception are available, or that the
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future was cancelled.
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"""
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return self._state != _PENDING
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def result(self):
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"""Return the result this future represents.
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If the future has been cancelled, raises CancelledError. If the
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future's result isn't yet available, raises InvalidStateError. If
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the future is done and has an exception set, this exception is raised.
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"""
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if self._state == _CANCELLED:
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exc = self._make_cancelled_error()
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raise exc
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if self._state != _FINISHED:
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raise exceptions.InvalidStateError('Result is not ready.')
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self.__log_traceback = False
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if self._exception is not None:
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raise self._exception
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return self._result
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def exception(self):
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"""Return the exception that was set on this future.
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The exception (or None if no exception was set) is returned only if
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the future is done. If the future has been cancelled, raises
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CancelledError. If the future isn't done yet, raises
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InvalidStateError.
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"""
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if self._state == _CANCELLED:
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exc = self._make_cancelled_error()
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raise exc
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if self._state != _FINISHED:
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raise exceptions.InvalidStateError('Exception is not set.')
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self.__log_traceback = False
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return self._exception
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def add_done_callback(self, fn, *, context=None):
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"""Add a callback to be run when the future becomes done.
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The callback is called with a single argument - the future object. If
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the future is already done when this is called, the callback is
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scheduled with call_soon.
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"""
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if self._state != _PENDING:
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self._loop.call_soon(fn, self, context=context)
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else:
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if context is None:
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context = contextvars.copy_context()
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self._callbacks.append((fn, context))
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# New method not in PEP 3148.
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def remove_done_callback(self, fn):
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"""Remove all instances of a callback from the "call when done" list.
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Returns the number of callbacks removed.
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"""
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filtered_callbacks = [(f, ctx)
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for (f, ctx) in self._callbacks
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if f != fn]
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removed_count = len(self._callbacks) - len(filtered_callbacks)
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if removed_count:
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self._callbacks[:] = filtered_callbacks
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return removed_count
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# So-called internal methods (note: no set_running_or_notify_cancel()).
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def set_result(self, result):
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"""Mark the future done and set its result.
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If the future is already done when this method is called, raises
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InvalidStateError.
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"""
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if self._state != _PENDING:
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raise exceptions.InvalidStateError(f'{self._state}: {self!r}')
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self._result = result
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self._state = _FINISHED
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self.__schedule_callbacks()
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def set_exception(self, exception):
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"""Mark the future done and set an exception.
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If the future is already done when this method is called, raises
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InvalidStateError.
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"""
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if self._state != _PENDING:
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raise exceptions.InvalidStateError(f'{self._state}: {self!r}')
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if isinstance(exception, type):
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exception = exception()
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if type(exception) is StopIteration:
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raise TypeError("StopIteration interacts badly with generators "
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"and cannot be raised into a Future")
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self._exception = exception
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self._state = _FINISHED
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self.__schedule_callbacks()
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self.__log_traceback = True
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def __await__(self):
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if not self.done():
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self._asyncio_future_blocking = True
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yield self # This tells Task to wait for completion.
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if not self.done():
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raise RuntimeError("await wasn't used with future")
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return self.result() # May raise too.
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__iter__ = __await__ # make compatible with 'yield from'.
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# Needed for testing purposes.
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_PyFuture = Future
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def _get_loop(fut):
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# Tries to call Future.get_loop() if it's available.
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# Otherwise fallbacks to using the old '_loop' property.
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try:
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get_loop = fut.get_loop
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except AttributeError:
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pass
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else:
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return get_loop()
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return fut._loop
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def _set_result_unless_cancelled(fut, result):
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"""Helper setting the result only if the future was not cancelled."""
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if fut.cancelled():
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return
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fut.set_result(result)
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def _convert_future_exc(exc):
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exc_class = type(exc)
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if exc_class is concurrent.futures.CancelledError:
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return exceptions.CancelledError(*exc.args)
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elif exc_class is concurrent.futures.TimeoutError:
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return exceptions.TimeoutError(*exc.args)
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elif exc_class is concurrent.futures.InvalidStateError:
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return exceptions.InvalidStateError(*exc.args)
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else:
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return exc
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def _set_concurrent_future_state(concurrent, source):
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"""Copy state from a future to a concurrent.futures.Future."""
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assert source.done()
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if source.cancelled():
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concurrent.cancel()
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if not concurrent.set_running_or_notify_cancel():
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return
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exception = source.exception()
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if exception is not None:
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concurrent.set_exception(_convert_future_exc(exception))
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else:
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result = source.result()
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concurrent.set_result(result)
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def _copy_future_state(source, dest):
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"""Internal helper to copy state from another Future.
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The other Future may be a concurrent.futures.Future.
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"""
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assert source.done()
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if dest.cancelled():
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return
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assert not dest.done()
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if source.cancelled():
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dest.cancel()
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else:
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exception = source.exception()
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if exception is not None:
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dest.set_exception(_convert_future_exc(exception))
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else:
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result = source.result()
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dest.set_result(result)
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def _chain_future(source, destination):
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"""Chain two futures so that when one completes, so does the other.
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The result (or exception) of source will be copied to destination.
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If destination is cancelled, source gets cancelled too.
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Compatible with both asyncio.Future and concurrent.futures.Future.
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"""
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if not isfuture(source) and not isinstance(source,
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concurrent.futures.Future):
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raise TypeError('A future is required for source argument')
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if not isfuture(destination) and not isinstance(destination,
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concurrent.futures.Future):
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raise TypeError('A future is required for destination argument')
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source_loop = _get_loop(source) if isfuture(source) else None
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dest_loop = _get_loop(destination) if isfuture(destination) else None
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def _set_state(future, other):
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if isfuture(future):
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_copy_future_state(other, future)
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else:
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_set_concurrent_future_state(future, other)
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def _call_check_cancel(destination):
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if destination.cancelled():
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if source_loop is None or source_loop is dest_loop:
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source.cancel()
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else:
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source_loop.call_soon_threadsafe(source.cancel)
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def _call_set_state(source):
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if (destination.cancelled() and
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dest_loop is not None and dest_loop.is_closed()):
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return
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if dest_loop is None or dest_loop is source_loop:
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_set_state(destination, source)
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else:
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dest_loop.call_soon_threadsafe(_set_state, destination, source)
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destination.add_done_callback(_call_check_cancel)
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source.add_done_callback(_call_set_state)
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def wrap_future(future, *, loop=None):
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"""Wrap concurrent.futures.Future object."""
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if isfuture(future):
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return future
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assert isinstance(future, concurrent.futures.Future), \
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f'concurrent.futures.Future is expected, got {future!r}'
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if loop is None:
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loop = events._get_event_loop()
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new_future = loop.create_future()
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_chain_future(future, new_future)
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return new_future
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try:
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import _asyncio
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except ImportError:
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pass
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else:
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# _CFuture is needed for tests.
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Future = _CFuture = _asyncio.Future
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