[Spice-devel] [PATCH spice-gtk v2] Add SpiceSession::disconnected signal

[Frediano Ziglio]

> 
> Previously, an application was required to determine whether a session
> had been disconnected by listening for the SpiceSession::channel-destroy
> signal for each individual channel. The Application had to keep track of
> whether all channels had been destroyed.
> 
> An additional difficulty is that when a SpiceSession::channel-destroy
> signal is emitted, the channel object has not been freed yet, so any
> shutdown/de-allocation actions have not yet happened. This became
> significant since virt-viewer exits the application in response to the
> last 'channel-destroy' signal, which means that the channel objects are
> never properly freed. This is particularly problematic for the usbredir
> channel, which might need to disconnect USB devices asynchronously, and
> if the application exits before that process has completed, the USB
> devices may not be available on the client machine.
> 
> With this patch, the SpiceSession still emits the 'channel-destroy'
> signal for each channel when it is disconnected. But it also internally
> tracks which channels have been destroyed, and waits for them to be
> freed. When all channels are freed, it emits an additional
> 'disconnected' signal.  An application can be confident that all
> channels have been freed by this point, and the application can exit
> safely.
> ---
> Changes in v2:
>  - remove ABI change ('disconnected' vfunc in SpiceSession struct
>  - use an integer to track disconnecting channels instead of a list of
>    objects
>  - Add a warning to spice_session_dispose() if there are channels
>    disconnecting when the session is destroyed.
> 
>  src/spice-session.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/src/spice-session.c b/src/spice-session.c
> index 57acc63..1731904 100644
> --- a/src/spice-session.c
> +++ b/src/spice-session.c
> @@ -94,6 +94,7 @@ struct _SpiceSessionPrivate {
>      int               protocol;
>      SpiceChannel      *cmain; /* weak reference */
>      Ring              channels;
> +    guint             channels_destroying;
>      guint32           mm_time;
>      gboolean          client_provided_sockets;
>      guint64           mm_time_at_clock;
> @@ -210,6 +211,7 @@ enum {
>      SPICE_SESSION_CHANNEL_NEW,
>      SPICE_SESSION_CHANNEL_DESTROY,
>      SPICE_SESSION_MM_TIME_RESET,
> +    SPICE_SESSION_DISCONNECTED,
>      SPICE_SESSION_LAST_SIGNAL,
>  };
>  
> @@ -343,6 +345,7 @@ spice_session_dispose(GObject *gobject)
>      g_warn_if_fail(s->migration_left == NULL);
>      g_warn_if_fail(s->after_main_init == 0);
>      g_warn_if_fail(s->disconnecting == 0);
> +    g_warn_if_fail(s->channels_destroying == 0);
>  
>      g_clear_object(&s->audio_manager);
>      g_clear_object(&s->usb_manager);
> @@ -1313,6 +1316,22 @@ static void spice_session_class_init(SpiceSessionClass
> *klass)
>                       1,
>                       SPICE_TYPE_CHANNEL);
>  
> +    /**
> +     * SpiceSession::disconnected:
> +     * @session: the session that emitted the signal
> +     *
> +     * The #SpiceSession::disconnected signal is emitted when all channels
> have been destroyed.
> +     **/
> +    signals[SPICE_SESSION_DISCONNECTED] =
> +        g_signal_new("disconnected",
> +                     G_OBJECT_CLASS_TYPE(gobject_class),
> +                     G_SIGNAL_RUN_FIRST,
> +                     0, NULL, NULL,
> +                     g_cclosure_marshal_VOID__VOID,
> +                     G_TYPE_NONE,
> +                     0,
> +                     NULL);
> +
>      /**
>       * SpiceSession::mm-time-reset:
>       * @session: the session that emitted the signal
> @@ -2269,6 +2288,17 @@ void spice_session_channel_new(SpiceSession *session,
> SpiceChannel *channel)
>      g_signal_emit(session, signals[SPICE_SESSION_CHANNEL_NEW], 0, channel);
>  }
>  
> +static void channel_finally_destroyed(gpointer data, GObject *channel)
> +{
> +    SpiceSession *session = SPICE_SESSION(data);
> +    SpiceSessionPrivate *s = session->priv;
> +    s->channels_destroying--;
> +    if (s->channels_destroying == 0) {

I would also check that the ring of channel on session is empty.
In theory you could have still active channels not counted in channels_destroying.
Maybe I'm too paranoid but the code path is not hot and surely is safer
to do the check.

> +        g_signal_emit(session, signals[SPICE_SESSION_DISCONNECTED], 0);
> +    }
> +    g_object_unref(session);
> +}
> +
>  static void spice_session_channel_destroy(SpiceSession *session,
>  SpiceChannel *channel)
>  {
>      g_return_if_fail(SPICE_IS_SESSION(session));
> @@ -2302,6 +2332,12 @@ static void spice_session_channel_destroy(SpiceSession
> *session, SpiceChannel *c
>  
>      g_clear_object(&channel->priv->session);
>      spice_channel_disconnect(channel, SPICE_CHANNEL_NONE);
> +
> +    /* Wait until the channel is properly freed so that we can emit a
> +     * 'disconnected' signal */
> +    s->channels_destroying++;
> +    g_object_weak_ref(G_OBJECT(channel), channel_finally_destroyed,
> g_object_ref(session));
> +
>      g_object_unref(channel);
>  }
>  

Frediano