[tarantool-patches] Re: [PATCH] Fix fiber_join() hang in case fiber_cancel() was called
Serge Petrenko
sergepetrenko at tarantool.org
Tue Feb 5 18:02:58 MSK 2019
> 5 февр. 2019 г., в 12:00, Vladimir Davydov <vdavydov.dev at gmail.com> написал(а):
>
> On Tue, Feb 05, 2019 at 09:28:01AM +0300, Serge Petrenko wrote:
>>
>>
>>> 4 февр. 2019 г., в 20:44, Vladimir Davydov <vdavydov.dev at gmail.com> написал(а):
>>>
>>>>
>>>> diff --git a/src/fiber.c b/src/fiber.c
>>>> index 6f3d0ab78..4dc6b3c5a 100644
>>>> --- a/src/fiber.c
>>>> +++ b/src/fiber.c
>>>> @@ -392,9 +392,17 @@ fiber_join(struct fiber *fiber)
>>>> assert(fiber->flags & FIBER_IS_JOINABLE);
>>>>
>>>> if (! fiber_is_dead(fiber)) {
>>>> - rlist_add_tail_entry(&fiber->wake, fiber(), state);
>>>>
>>>> do {
>>>> + /*
>>>> + * In case fiber is cancelled during yield
>>>> + * it will be removed from wake queue by a
>>>> + * wakeup following the cancel.
>>>> + * Having multiple entries for the same fiber
>>>> + * doesn't hurt, since wakeup is executed only
>>>> + * once per fiber.
>>>> + */
>>>> + rlist_add_tail_entry(&fiber->wake, fiber(), state);
>>>
>>> I don't quite like the idea that cancelling a fiber that is joining
>>> another fiber will have no effect until the other fiber has exited.
>>> Can't we break the loop if fiber_is_cancelled()?
>>
>> We can do that. But then we have to set FIBER_IS_JOINABLE to false
>> for the joined fiber so that it executes fiber_recycle().
>
> Why should we? IMO the user should be free to kill a fiber executing
> fiber_join. If that happens, the joinable fiber shouldn't be collected
> until another fiber joins it successfully. This would be consistent with
> pthread_join behavior.
>
>> Otherwise it will leak. Is it ok?
As discussed verbally, on cancellation lets make the fiber non-joinable and exit.
I addressed your other comments in v2. Please, take a look.
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