Re: [Tarantool-patches] [PATCH 1/1] fiber_cond: remove rlist_shift usages

[Cyrill Gorcunov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

On Tue, Mar 02, 2021 at 10:37:36AM +0300, Cyrill Gorcunov wrote:
> On Mon, Mar 01, 2021 at 11:23:13PM +0100, Vladislav Shpilevoy wrote:
> > @@ -94,7 +94,7 @@ fiber_cond_broadcast(struct fiber_cond *e)
> >  {
> >  	while (! rlist_empty(&e->waiters)) {
> >  		struct fiber *f;
> > -		f = rlist_shift_entry(&e->waiters, struct fiber, state);
> > +		f = rlist_first_entry(&e->waiters, struct fiber, state);
> >  		fiber_wakeup(f);
> >  	}
> >  }
> 
> The fiber_wakeup ignores
> 
> 	if (f->flags & (FIBER_IS_READY | FIBER_IS_DEAD))
> 		return;
> 
> can't we hit the situation where fiber_cond_broadcast called with
> dead fiber so that it won't be deleted from the list with new code?
> 
> Actually looking into fiber_loop code I see
> 
> static void
> fiber_loop(MAYBE_UNUSED void *data)
> {
> 	...
> 	fiber->flags |= FIBER_IS_DEAD;
> 	while (! rlist_empty(&fiber->wake)) {
> 		       struct fiber *f;
> 		       f = rlist_shift_entry(&fiber->wake, struct fiber,
> 					     state);
> 		       assert(f != fiber);
> 		       fiber_wakeup(f);
> 	}
> 
> so it should be safe with your patch, but just to make sure I didn't
> miss something obvious.

Still, Ack. The prev mail was just to share some thoughts.