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44 lines
1.3 KiB
Python
44 lines
1.3 KiB
Python
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from asyncio.locks import Lock as _Lock
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from asyncio import coroutine
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from asyncio import futures
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# Fixes an issue with all Python versions that leaves pending waiters
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# without being awakened when the first waiter is canceled.
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# Code adapted from the PR https://github.com/python/cpython/pull/1031
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# Waiting once it is merged to make a proper condition to relay on
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# the stdlib implementation or this one patched
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class Lock(_Lock):
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@coroutine
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def acquire(self):
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"""Acquire a lock.
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This method blocks until the lock is unlocked, then sets it to
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locked and returns True.
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"""
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if not self._locked and all(w.cancelled() for w in self._waiters):
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self._locked = True
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return True
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fut = self._loop.create_future()
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self._waiters.append(fut)
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try:
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yield from fut
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self._locked = True
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return True
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except futures.CancelledError:
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if not self._locked: # pragma: no cover
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self._wake_up_first()
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raise
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finally:
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self._waiters.remove(fut)
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def _wake_up_first(self):
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"""Wake up the first waiter who isn't cancelled."""
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for fut in self._waiters:
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if not fut.done():
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fut.set_result(True)
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break
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