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

[Stefan Hajnoczi <stefanha@gmail.com>]

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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/

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 :).

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