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bpo-27585: Cancelled lock waiter wakes up the next one #1031

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Merged
1st1 merged 1 commit into from
Jun 9, 2017
Merged

bpo-27585: Cancelled lock waiter wakes up the next one #1031

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17 changes: 12 additions & 5 deletions Lib/asyncio/locks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,10 @@ def acquire(self):
yield from fut
self._locked = True
return True
except futures.CancelledError:
if not self._locked:
self._wake_up_first()
raise
finally:
self._waiters.remove(fut)

Expand All @@ -192,14 +196,17 @@ def release(self):
"""
if self._locked:
self._locked = False
# Wake up the first waiter who isn't cancelled.
for fut in self._waiters:
if not fut.done():
fut.set_result(True)
break
self._wake_up_first()
else:
raise RuntimeError('Lock is not acquired.')

def _wake_up_first(self):
"""Wake up the first waiter who isn't cancelled."""
for fut in self._waiters:
if not fut.done():
fut.set_result(True)
break


class Event:
"""Asynchronous equivalent to threading.Event.
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22 changes: 22 additions & 0 deletions Lib/test/test_asyncio/test_locks.py
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,28 @@ def lockit(name, blocker):
self.assertTrue(tb.cancelled())
self.assertTrue(tc.done())

def test_finished_waiter_cancelled(self):
lock = asyncio.Lock(loop=self.loop)

ta = asyncio.Task(lock.acquire(), loop=self.loop)
test_utils.run_briefly(self.loop)
self.assertTrue(lock.locked())

tb = asyncio.Task(lock.acquire(), loop=self.loop)
test_utils.run_briefly(self.loop)
self.assertEqual(len(lock._waiters), 1)

# Create a second waiter, wake up the first, and cancel it.
# Without the fix, the second was not woken up.
tc = asyncio.Task(lock.acquire(), loop=self.loop)
lock.release()
tb.cancel()
test_utils.run_briefly(self.loop)

self.assertTrue(lock.locked())
self.assertTrue(ta.done())
self.assertTrue(tb.cancelled())

def test_release_not_acquired(self):
lock = asyncio.Lock(loop=self.loop)

Expand Down