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

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Nov 20, 2017 at 08:45:21AM -0500, Jeff Cody wrote:
> 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:
> > 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?

Sure.

Stefan

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