bpo-32841: Fix cancellation in awaiting asyncio.Condition (#5665)

Author: bharel

Lib/asyncio/locks.py

@@ -358,12 +358,16 @@ async def wait(self):
 
  finally:
  # Must reacquire lock even if wait is cancelled
+ cancelled = False
  while True:
  try:
  await self.acquire()
  break
  except futures.CancelledError:
- pass
+ cancelled = True
+
+ if cancelled:
+ raise futures.CancelledError
 
  async def wait_for(self, predicate):
  """Wait until a predicate becomes true.

Lib/test/test_asyncio/test_locks.py

@@ -214,11 +214,11 @@ async def lockit():
  call_count += 1
  await lock.acquire()
  lock_count += 1
- 
+
  async def lockandtrigger():
  await lock.acquire()
  self.loop.call_soon(trigger)
- 
+
  def trigger():
  t1.cancel()
  lock.release()
@@ -248,8 +248,6 @@ def trigger():
  test_utils.run_briefly(self.loop)
  self.assertTrue(t3.cancelled())
 
-
-
  def test_finished_waiter_cancelled(self):
  lock = asyncio.Lock(loop=self.loop)
 
@@ -576,6 +574,31 @@ def test_wait_cancel_contested(self):
 
  self.assertTrue(cond.locked())
 
+ def test_wait_cancel_after_notify(self):
+ # See bpo-32841
+ cond = asyncio.Condition(loop=self.loop)
+ waited = False
+
+ async def wait_on_cond():
+ nonlocal waited
+ async with cond:
+ waited = True # Make sure this area was reached
+ await cond.wait()
+
+ waiter = asyncio.ensure_future(wait_on_cond(), loop=self.loop)
+ test_utils.run_briefly(self.loop) # Start waiting
+
+ self.loop.run_until_complete(cond.acquire())
+ cond.notify()
+ test_utils.run_briefly(self.loop) # Get to acquire()
+ waiter.cancel()
+ test_utils.run_briefly(self.loop) # Activate cancellation
+ cond.release()
+ test_utils.run_briefly(self.loop) # Cancellation should occur
+
+ self.assertTrue(waiter.cancelled())
+ self.assertTrue(waited)
+
  def test_wait_unacquired(self):
  cond = asyncio.Condition(loop=self.loop)
  self.assertRaises(

Misc/NEWS.d/next/Library/2018-02-14-00-21-24.bpo-32841.bvHDOc.rst

@@ -0,0 +1,2 @@
+Fixed `asyncio.Condition` issue which silently ignored cancellation after
+notifying and cancelling a conditional lock. Patch by Bar Harel.