[Spice-devel] [PATCH spice-gtk 11/13] coroutine: reference object when signaling

[Christophe Fergeau]

Hey,

On Sun, Nov 09, 2014 at 05:31:43PM +0100, Marc-André Lureau wrote:
> Before the signal is acutally emitted, the channel may be

'actually'

> released. Similarly to g_signal_emit, take a reference before yielding
> to main context.

I would drop the "similarly to g_signal_emit" as your purpose is most
likely different. The ref is needed here as the signal emission is
async, so code can run before the signal emission, but g_signal_emit is
synchronous.

I assume the scenario you want to protect against is
- (coroutine context)g_coroutine_signal_emit is called
  - the signal emission is scheduled in an idle with g_idle_add
  - coroutine_yield() is called
- (main context)code runs which drops the last ref on the channel
- (main context)idle runs and tries to emit the signal


Patch looks good if this is the correct scenario.

Christophe

> ---
>  gtk/gio-coroutine.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/gtk/gio-coroutine.c b/gtk/gio-coroutine.c
> index c903bd2..c866e15 100644
> --- a/gtk/gio-coroutine.c
> +++ b/gtk/gio-coroutine.c
> @@ -222,9 +222,11 @@ g_coroutine_signal_emit(gpointer instance, guint signal_id,
>      if (coroutine_self_is_main()) {
>          g_signal_emit_valist(instance, signal_id, detail, data.var_args);
>      } else {
> +        g_object_ref(instance);
>          g_idle_add(emit_main_context, &data);
>          coroutine_yield(NULL);
>          g_warn_if_fail(data.notified);
> +        g_object_unref(instance);
>      }
>  
>      va_end (data.var_args);
> @@ -253,7 +255,7 @@ void g_coroutine_object_notify(GObject *object,
>          g_object_notify(object, property_name);
>      } else {
>  
> -        data.instance = object;
> +        data.instance = g_object_ref(object);
>          data.caller = coroutine_self();
>          data.propname = (gpointer)property_name;
>          data.notified = FALSE;
> @@ -268,5 +270,6 @@ void g_coroutine_object_notify(GObject *object,
>           */
>          coroutine_yield(NULL);
>          g_warn_if_fail(data.notified);
> +        g_object_unref(object);
>      }
>  }
> -- 
> 1.9.3
> 
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