anonymous2017 added the comment: I may have mis-characterized the original report. Rephrasing just to make sure it is correctly addressed:
First, it is not about fairness. Sorry for the original characterization. I was trying to understand what was happening. Second, the precise issue is whether a `yield from` can be relied upon for cooperative multitasking. Should other co-routines should be prevented from running or delayed if one routine is running and acquiring and releasing a lock using `yield from`. It seemed at first sight that `yield from <anything>` should give the scheduler a chance to consider other routines. But the lock code above and including line #171 does not give control to the scheduler in a special case: https://github.com/python/cpython/blob/master/Lib/asyncio/locks.py#L171 Code Sample 1 (shows b() being delayed until a() is fully complete despite a() yielding many times) ============= import asyncio lock = asyncio.Lock() def a (): yield from lock.acquire() for i in range(10): print('b: ' + str(i)) if i % 2 == 0: lock.release() yield from lock.acquire() lock.release() async def b (): print('hello') asyncio.get_event_loop().run_until_complete(asyncio.gather(a(), b())) print('done') Code Sample 2 ============= (shows interleaving if an additional INITIAL yield from asyncio.sleep is inserted; removing the initial sleep removes the interleaving) import asyncio lock = asyncio.Lock() def a (): yield from lock.acquire() yield from asyncio.sleep(0) for i in range(10): print('a: ' + str(i)) if i % 2 == 0: lock.release() yield from lock.acquire() lock.release() def b (): yield from lock.acquire() yield from asyncio.sleep(0) for i in range(10): print('b: ' + str(i)) if i % 2 == 0: lock.release() yield from lock.acquire() lock.release() asyncio.get_event_loop().run_until_complete(asyncio.gather(a(), b())) print('done') Thank you for your kind consideration. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue29303> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
