mirror of https://github.com/python/cpython
652 lines
22 KiB
Python
652 lines
22 KiB
Python
"""Support for tasks, coroutines and the scheduler."""
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__all__ = ['Task',
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'FIRST_COMPLETED', 'FIRST_EXCEPTION', 'ALL_COMPLETED',
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'wait', 'wait_for', 'as_completed', 'sleep', 'async',
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'gather', 'shield',
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]
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import concurrent.futures
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import functools
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import inspect
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import linecache
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import sys
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import traceback
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import weakref
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from . import coroutines
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from . import events
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from . import futures
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from .coroutines import coroutine
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from .log import logger
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_PY34 = (sys.version_info >= (3, 4))
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_PY35 = (sys.version_info >= (3, 5))
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class Task(futures.Future):
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"""A coroutine wrapped in a Future."""
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# An important invariant maintained while a Task not done:
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#
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# - Either _fut_waiter is None, and _step() is scheduled;
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# - or _fut_waiter is some Future, and _step() is *not* scheduled.
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#
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# The only transition from the latter to the former is through
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# _wakeup(). When _fut_waiter is not None, one of its callbacks
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# must be _wakeup().
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# Weak set containing all tasks alive.
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_all_tasks = weakref.WeakSet()
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# Dictionary containing tasks that are currently active in
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# all running event loops. {EventLoop: Task}
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_current_tasks = {}
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@classmethod
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def current_task(cls, loop=None):
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"""Return the currently running task in an event loop or None.
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By default the current task for the current event loop is returned.
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None is returned when called not in the context of a Task.
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"""
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if loop is None:
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loop = events.get_event_loop()
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return cls._current_tasks.get(loop)
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@classmethod
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def all_tasks(cls, loop=None):
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"""Return a set of all tasks for an event loop.
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By default all tasks for the current event loop are returned.
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"""
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if loop is None:
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loop = events.get_event_loop()
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return {t for t in cls._all_tasks if t._loop is loop}
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def __init__(self, coro, *, loop=None):
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assert coroutines.iscoroutine(coro), repr(coro) # Not a coroutine function!
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super().__init__(loop=loop)
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if self._source_traceback:
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del self._source_traceback[-1]
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self._coro = iter(coro) # Use the iterator just in case.
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self._fut_waiter = None
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self._must_cancel = False
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self._loop.call_soon(self._step)
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self.__class__._all_tasks.add(self)
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# If False, don't log a message if the task is destroyed whereas its
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# status is still pending
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self._log_destroy_pending = True
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# On Python 3.3 or older, objects with a destructor part of a reference
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# cycle are never destroyed. It's not more the case on Python 3.4 thanks to
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# the PEP 442.
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if _PY34:
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def __del__(self):
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if self._state == futures._PENDING and self._log_destroy_pending:
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context = {
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'task': self,
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'message': 'Task was destroyed but it is pending!',
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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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futures.Future.__del__(self)
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def __repr__(self):
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info = []
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if self._must_cancel:
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info.append('cancelling')
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else:
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info.append(self._state.lower())
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info.append(coroutines._format_coroutine(self._coro))
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if self._state == futures._FINISHED:
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info.append(self._format_result())
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if self._callbacks:
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info.append(self._format_callbacks())
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if self._fut_waiter is not None:
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info.append('wait_for=%r' % self._fut_waiter)
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return '<%s %s>' % (self.__class__.__name__, ' '.join(info))
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def get_stack(self, *, limit=None):
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"""Return the list of stack frames for this task's coroutine.
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If the coroutine is active, this returns the stack where it is
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suspended. If the coroutine has completed successfully or was
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cancelled, this returns an empty list. If the coroutine was
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terminated by an exception, this returns the list of traceback
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frames.
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The frames are always ordered from oldest to newest.
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The optional limit gives the maximum number of frames to
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return; by default all available frames are returned. Its
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meaning differs depending on whether a stack or a traceback is
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returned: the newest frames of a stack are returned, but the
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oldest frames of a traceback are returned. (This matches the
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behavior of the traceback module.)
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For reasons beyond our control, only one stack frame is
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returned for a suspended coroutine.
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"""
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frames = []
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f = self._coro.gi_frame
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if f is not None:
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while f is not None:
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if limit is not None:
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if limit <= 0:
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break
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limit -= 1
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frames.append(f)
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f = f.f_back
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frames.reverse()
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elif self._exception is not None:
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tb = self._exception.__traceback__
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while tb is not None:
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if limit is not None:
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if limit <= 0:
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break
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limit -= 1
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frames.append(tb.tb_frame)
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tb = tb.tb_next
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return frames
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def print_stack(self, *, limit=None, file=None):
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"""Print the stack or traceback for this task's coroutine.
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This produces output similar to that of the traceback module,
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for the frames retrieved by get_stack(). The limit argument
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is passed to get_stack(). The file argument is an I/O stream
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to which the output goes; by default it goes to sys.stderr.
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"""
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extracted_list = []
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checked = set()
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for f in self.get_stack(limit=limit):
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lineno = f.f_lineno
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co = f.f_code
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filename = co.co_filename
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name = co.co_name
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if filename not in checked:
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checked.add(filename)
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linecache.checkcache(filename)
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line = linecache.getline(filename, lineno, f.f_globals)
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extracted_list.append((filename, lineno, name, line))
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exc = self._exception
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if not extracted_list:
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print('No stack for %r' % self, file=file)
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elif exc is not None:
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print('Traceback for %r (most recent call last):' % self,
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file=file)
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else:
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print('Stack for %r (most recent call last):' % self,
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file=file)
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traceback.print_list(extracted_list, file=file)
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if exc is not None:
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for line in traceback.format_exception_only(exc.__class__, exc):
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print(line, file=file, end='')
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def cancel(self):
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"""Request this task to cancel itself.
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This arranges for a CancelledError to be thrown into the
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wrapped coroutine on the next cycle through the event loop.
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The coroutine then has a chance to clean up or even deny
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the request using try/except/finally.
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Contrary to Future.cancel(), this does not guarantee that the
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task will be cancelled: the exception might be caught and
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acted upon, delaying cancellation of the task or preventing it
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completely. The task may also return a value or raise a
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different exception.
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Immediately after this method is called, Task.cancelled() will
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not return True (unless the task was already cancelled). A
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task will be marked as cancelled when the wrapped coroutine
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terminates with a CancelledError exception (even if cancel()
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was not called).
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"""
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if self.done():
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return False
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if self._fut_waiter is not None:
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if self._fut_waiter.cancel():
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# Leave self._fut_waiter; it may be a Task that
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# catches and ignores the cancellation so we may have
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# to cancel it again later.
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return True
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# It must be the case that self._step is already scheduled.
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self._must_cancel = True
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return True
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def _step(self, value=None, exc=None):
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assert not self.done(), \
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'_step(): already done: {!r}, {!r}, {!r}'.format(self, value, exc)
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if self._must_cancel:
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if not isinstance(exc, futures.CancelledError):
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exc = futures.CancelledError()
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self._must_cancel = False
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coro = self._coro
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self._fut_waiter = None
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self.__class__._current_tasks[self._loop] = self
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# Call either coro.throw(exc) or coro.send(value).
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try:
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if exc is not None:
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result = coro.throw(exc)
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elif value is not None:
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result = coro.send(value)
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else:
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result = next(coro)
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except StopIteration as exc:
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self.set_result(exc.value)
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except futures.CancelledError as exc:
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super().cancel() # I.e., Future.cancel(self).
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except Exception as exc:
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self.set_exception(exc)
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except BaseException as exc:
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self.set_exception(exc)
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raise
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else:
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if isinstance(result, futures.Future):
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# Yielded Future must come from Future.__iter__().
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if result._blocking:
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result._blocking = False
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result.add_done_callback(self._wakeup)
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self._fut_waiter = result
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if self._must_cancel:
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if self._fut_waiter.cancel():
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self._must_cancel = False
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else:
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self._loop.call_soon(
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self._step, None,
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RuntimeError(
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'yield was used instead of yield from '
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'in task {!r} with {!r}'.format(self, result)))
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elif result is None:
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# Bare yield relinquishes control for one event loop iteration.
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self._loop.call_soon(self._step)
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elif inspect.isgenerator(result):
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# Yielding a generator is just wrong.
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self._loop.call_soon(
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self._step, None,
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RuntimeError(
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'yield was used instead of yield from for '
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'generator in task {!r} with {}'.format(
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self, result)))
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else:
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# Yielding something else is an error.
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self._loop.call_soon(
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self._step, None,
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RuntimeError(
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'Task got bad yield: {!r}'.format(result)))
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finally:
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self.__class__._current_tasks.pop(self._loop)
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self = None # Needed to break cycles when an exception occurs.
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def _wakeup(self, future):
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try:
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value = future.result()
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except Exception as exc:
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# This may also be a cancellation.
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self._step(None, exc)
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else:
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self._step(value, None)
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self = None # Needed to break cycles when an exception occurs.
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# wait() and as_completed() similar to those in PEP 3148.
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FIRST_COMPLETED = concurrent.futures.FIRST_COMPLETED
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FIRST_EXCEPTION = concurrent.futures.FIRST_EXCEPTION
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ALL_COMPLETED = concurrent.futures.ALL_COMPLETED
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@coroutine
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def wait(fs, *, loop=None, timeout=None, return_when=ALL_COMPLETED):
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"""Wait for the Futures and coroutines given by fs to complete.
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The sequence futures must not be empty.
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Coroutines will be wrapped in Tasks.
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Returns two sets of Future: (done, pending).
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Usage:
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done, pending = yield from asyncio.wait(fs)
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Note: This does not raise TimeoutError! Futures that aren't done
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when the timeout occurs are returned in the second set.
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"""
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if isinstance(fs, futures.Future) or coroutines.iscoroutine(fs):
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raise TypeError("expect a list of futures, not %s" % type(fs).__name__)
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if not fs:
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raise ValueError('Set of coroutines/Futures is empty.')
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if loop is None:
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loop = events.get_event_loop()
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fs = {async(f, loop=loop) for f in set(fs)}
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if return_when not in (FIRST_COMPLETED, FIRST_EXCEPTION, ALL_COMPLETED):
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raise ValueError('Invalid return_when value: {}'.format(return_when))
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return (yield from _wait(fs, timeout, return_when, loop))
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def _release_waiter(waiter, value=True, *args):
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if not waiter.done():
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waiter.set_result(value)
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@coroutine
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def wait_for(fut, timeout, *, loop=None):
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"""Wait for the single Future or coroutine to complete, with timeout.
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Coroutine will be wrapped in Task.
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Returns result of the Future or coroutine. When a timeout occurs,
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it cancels the task and raises TimeoutError. To avoid the task
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cancellation, wrap it in shield().
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Usage:
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result = yield from asyncio.wait_for(fut, 10.0)
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"""
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if loop is None:
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loop = events.get_event_loop()
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if timeout is None:
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return (yield from fut)
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waiter = futures.Future(loop=loop)
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timeout_handle = loop.call_later(timeout, _release_waiter, waiter, False)
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cb = functools.partial(_release_waiter, waiter, True)
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fut = async(fut, loop=loop)
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fut.add_done_callback(cb)
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try:
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if (yield from waiter):
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return fut.result()
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else:
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fut.remove_done_callback(cb)
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fut.cancel()
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raise futures.TimeoutError()
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finally:
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timeout_handle.cancel()
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@coroutine
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def _wait(fs, timeout, return_when, loop):
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"""Internal helper for wait() and _wait_for().
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The fs argument must be a collection of Futures.
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"""
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assert fs, 'Set of Futures is empty.'
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waiter = futures.Future(loop=loop)
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timeout_handle = None
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if timeout is not None:
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timeout_handle = loop.call_later(timeout, _release_waiter, waiter)
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counter = len(fs)
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def _on_completion(f):
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nonlocal counter
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counter -= 1
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if (counter <= 0 or
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return_when == FIRST_COMPLETED or
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return_when == FIRST_EXCEPTION and (not f.cancelled() and
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f.exception() is not None)):
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if timeout_handle is not None:
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timeout_handle.cancel()
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if not waiter.done():
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waiter.set_result(False)
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for f in fs:
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f.add_done_callback(_on_completion)
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try:
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yield from waiter
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finally:
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if timeout_handle is not None:
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timeout_handle.cancel()
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done, pending = set(), set()
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for f in fs:
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f.remove_done_callback(_on_completion)
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if f.done():
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done.add(f)
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else:
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pending.add(f)
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return done, pending
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# This is *not* a @coroutine! It is just an iterator (yielding Futures).
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def as_completed(fs, *, loop=None, timeout=None):
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"""Return an iterator whose values are coroutines.
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When waiting for the yielded coroutines you'll get the results (or
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exceptions!) of the original Futures (or coroutines), in the order
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in which and as soon as they complete.
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This differs from PEP 3148; the proper way to use this is:
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for f in as_completed(fs):
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result = yield from f # The 'yield from' may raise.
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# Use result.
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If a timeout is specified, the 'yield from' will raise
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TimeoutError when the timeout occurs before all Futures are done.
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Note: The futures 'f' are not necessarily members of fs.
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"""
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if isinstance(fs, futures.Future) or coroutines.iscoroutine(fs):
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raise TypeError("expect a list of futures, not %s" % type(fs).__name__)
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loop = loop if loop is not None else events.get_event_loop()
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todo = {async(f, loop=loop) for f in set(fs)}
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from .queues import Queue # Import here to avoid circular import problem.
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done = Queue(loop=loop)
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timeout_handle = None
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def _on_timeout():
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for f in todo:
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f.remove_done_callback(_on_completion)
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done.put_nowait(None) # Queue a dummy value for _wait_for_one().
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todo.clear() # Can't do todo.remove(f) in the loop.
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def _on_completion(f):
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if not todo:
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return # _on_timeout() was here first.
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todo.remove(f)
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done.put_nowait(f)
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if not todo and timeout_handle is not None:
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timeout_handle.cancel()
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@coroutine
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def _wait_for_one():
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f = yield from done.get()
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if f is None:
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# Dummy value from _on_timeout().
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raise futures.TimeoutError
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return f.result() # May raise f.exception().
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for f in todo:
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f.add_done_callback(_on_completion)
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if todo and timeout is not None:
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timeout_handle = loop.call_later(timeout, _on_timeout)
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for _ in range(len(todo)):
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yield _wait_for_one()
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@coroutine
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def sleep(delay, result=None, *, loop=None):
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"""Coroutine that completes after a given time (in seconds)."""
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future = futures.Future(loop=loop)
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h = future._loop.call_later(delay,
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future._set_result_unless_cancelled, result)
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try:
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return (yield from future)
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finally:
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h.cancel()
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def async(coro_or_future, *, loop=None):
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"""Wrap a coroutine in a future.
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If the argument is a Future, it is returned directly.
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"""
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if isinstance(coro_or_future, futures.Future):
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if loop is not None and loop is not coro_or_future._loop:
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raise ValueError('loop argument must agree with Future')
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return coro_or_future
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elif coroutines.iscoroutine(coro_or_future):
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if loop is None:
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loop = events.get_event_loop()
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task = loop.create_task(coro_or_future)
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if task._source_traceback:
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del task._source_traceback[-1]
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return task
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else:
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raise TypeError('A Future or coroutine is required')
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class _GatheringFuture(futures.Future):
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"""Helper for gather().
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This overrides cancel() to cancel all the children and act more
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like Task.cancel(), which doesn't immediately mark itself as
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cancelled.
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"""
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def __init__(self, children, *, loop=None):
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super().__init__(loop=loop)
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self._children = children
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|
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def cancel(self):
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if self.done():
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return False
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for child in self._children:
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child.cancel()
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return True
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|
|
|
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def gather(*coros_or_futures, loop=None, return_exceptions=False):
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|
"""Return a future aggregating results from the given coroutines
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|
or futures.
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|
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|
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.)
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|
"""
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|
arg_to_fut = {arg: async(arg, loop=loop) for arg in set(coros_or_futures)}
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|
children = [arg_to_fut[arg] for arg in coros_or_futures]
|
|
n = len(children)
|
|
if n == 0:
|
|
outer = futures.Future(loop=loop)
|
|
outer.set_result([])
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|
return outer
|
|
if loop is None:
|
|
loop = children[0]._loop
|
|
for fut in children:
|
|
if fut._loop is not loop:
|
|
raise ValueError("futures are tied to different event loops")
|
|
outer = _GatheringFuture(children, loop=loop)
|
|
nfinished = 0
|
|
results = [None] * n
|
|
|
|
def _done_callback(i, fut):
|
|
nonlocal nfinished
|
|
if outer._state != futures._PENDING:
|
|
if fut._exception is not None:
|
|
# Mark exception retrieved.
|
|
fut.exception()
|
|
return
|
|
if fut._state == futures._CANCELLED:
|
|
res = futures.CancelledError()
|
|
if not return_exceptions:
|
|
outer.set_exception(res)
|
|
return
|
|
elif fut._exception is not None:
|
|
res = fut.exception() # Mark exception retrieved.
|
|
if not return_exceptions:
|
|
outer.set_exception(res)
|
|
return
|
|
else:
|
|
res = fut._result
|
|
results[i] = res
|
|
nfinished += 1
|
|
if nfinished == n:
|
|
outer.set_result(results)
|
|
|
|
for i, fut in enumerate(children):
|
|
fut.add_done_callback(functools.partial(_done_callback, i))
|
|
return outer
|
|
|
|
|
|
def shield(arg, *, loop=None):
|
|
"""Wait for a future, shielding it from cancellation.
|
|
|
|
The statement
|
|
|
|
res = yield from shield(something())
|
|
|
|
is exactly equivalent to the statement
|
|
|
|
res = yield from 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 = yield from shield(something())
|
|
except CancelledError:
|
|
res = None
|
|
"""
|
|
inner = async(arg, loop=loop)
|
|
if inner.done():
|
|
# Shortcut.
|
|
return inner
|
|
loop = inner._loop
|
|
outer = futures.Future(loop=loop)
|
|
|
|
def _done_callback(inner):
|
|
if outer.cancelled():
|
|
# Mark inner's result as retrieved.
|
|
inner.cancelled() or 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
|