Re: [Qemu-devel] [Qemu-block] [PATCH 3/5] coroutines: abort if we try to enter a still-sleeping coroutine

[Jeff Cody <jcody@redhat.com>]

On Mon, Nov 20, 2017 at 11:43:34AM +0000, Stefan Hajnoczi wrote:
> On Sun, Nov 19, 2017 at 09:46:44PM -0500, Jeff Cody wrote:
> > diff --git a/include/qemu/coroutine_int.h b/include/qemu/coroutine_int.h
> > index 931cdc9..b071217 100644
> > --- a/include/qemu/coroutine_int.h
> > +++ b/include/qemu/coroutine_int.h
> > @@ -56,6 +56,8 @@ struct Coroutine {
> >  
> >      int scheduled;
> >  
> > +    int sleeping;
> 
> s/int/bool/
> 

OK.

> BTW an alternative to adding individual bools is to implement a finite
> state machine for the entire coroutine lifecycle.  A single function can
> validate all state transitions:
> 
>   void check_state_transition(CoState old, CoState new,
>                               const char *action)
>   {
>       const char *errmsg = fsm[old][new];
>       if (!errmsg) {
>           return; /* valid transition! */
>       }
> 
>       fprintf(stderr, "Cannot %s coroutine from %s state\n",
>               action, state_name[old]);
>       abort();
>   }
> 
> Specifying fsm[][] forces us to think through all possible state
> transitions.  This approach is proactive whereas adding bool flags is
> reactive since it only covers a subset of states that were encountered
> after crashes.  I'm not sure if it's worth it though :).

Interesting idea; maybe more for 2.12 instead of 2.11, though?

Jeff