Re: [tarantool-patches] Re: [PATCH] Fix fiber_join() hang in case fiber_cancel() was called

[Serge Petrenko <sergepetrenko@tarantool.org>]

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> 5 февр. 2019 г., в 12:00, Vladimir Davydov <vdavydov.dev@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@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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