[guido]

http://hg.python.org/cpython/rev/6bee0fdcba39 changeset: 87468:6bee0fdcba39 user: Guido van Rossum date: Sat Nov 23 15:09:16 2013 -0800 summary: asyncio: Change bounded semaphore into a subclass, like threading.[Bounded]Semaphore.

files: Lib/asyncio/locks.py | 36 ++++++++-------- Lib/test/test_asyncio/test_locks.py | 2 +- 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/Lib/asyncio/locks.py b/Lib/asyncio/locks.py --- a/Lib/asyncio/locks.py +++ b/Lib/asyncio/locks.py @@ -336,22 +336,15 @@

...

+class BoundedSemaphore(Semaphore): ... + def release(self): + if self._value >= self._bound_value: + raise ValueError('BoundedSemaphore released too many times') + super().release()

If there's a lock and parallelism involved, this release() implementation is vulnerable to races: any number of threads can see "self._value < self._bound_value" before one of them manages to call the superclass release(), and so self._value can become arbitrarily larger than self._bound_value. I fixed the same bug in threading's similar bounded semaphore class a few weeks ago.