[Spice-devel] [spice-gtk v2] channel-display: Use GHashTable to keep stream's structure

[Lukáš Hrázký]

On Wed, 2018-03-07 at 09:17 +0100, Victor Toso wrote:
> From: Victor Toso <me at victortoso.com>
> 
> The major issue with the current approach is that it relies on
> the ID from SpiceMsgDisplayStreamCreate to create the smallest 2^n
> sized array that could fit the stream's id as index.
> 
> This is potentially dangerous as the ID value is not documented and
> could have any uint32_t value. We depend on Spice server's
> implementation which currently defines max of 50 streams.
> 
> > /** Maximum number of streams created by spice-server */
> > #define NUM_STREAMS 50
> 
> The first ID has the value of 49* while the c->streams array would be
> allocated to 64. We could only benefit from allocating on high
> creating/removal of streams, which is not the case.
> 
> We can improve the above situations by using a hash table.
> 
> Signed-off-by: Victor Toso <victortoso at redhat.com>
> ---
> Changes from v2:
> * using g_direct_hash/equal instead of the integer
>   conterpart.
> * changed the signature from int to uint32_t for id in destroy_stream()
> 
>  src/channel-display.c | 73 ++++++++++++++++++++++-----------------------------
>  1 file changed, 32 insertions(+), 41 deletions(-)
> 
> diff --git a/src/channel-display.c b/src/channel-display.c
> index 2ea0922..ec94cf8 100644
> --- a/src/channel-display.c
> +++ b/src/channel-display.c
> @@ -63,8 +63,7 @@ struct _SpiceDisplayChannelPrivate {
>      SpicePaletteCache           palette_cache;
>      SpiceImageSurfaces          image_surfaces;
>      SpiceGlzDecoderWindow       *glz_window;
> -    display_stream              **streams;
> -    int                         nstreams;
> +    GHashTable                  *streams;
>      gboolean                    mark;
>      guint                       mark_false_event_id;
>      GArray                      *monitors;
> @@ -168,7 +167,7 @@ static void spice_display_channel_finalize(GObject *object)
>      g_clear_pointer(&c->monitors, g_array_unref);
>      clear_surfaces(SPICE_CHANNEL(object), FALSE);
>      g_hash_table_unref(c->surfaces);
> -    clear_streams(SPICE_CHANNEL(object));
> +    g_clear_pointer(&c->streams, g_hash_table_unref);
>      g_clear_pointer(&c->palettes, cache_free);
>  
>      if (G_OBJECT_CLASS(spice_display_channel_parent_class)->finalize)
> @@ -863,6 +862,7 @@ static void spice_display_channel_init(SpiceDisplayChannel *channel)
>      c = channel->priv = SPICE_DISPLAY_CHANNEL_GET_PRIVATE(channel);
>  
>      c->surfaces = g_hash_table_new_full(NULL, NULL, NULL, destroy_surface);
> +    c->streams = g_hash_table_new_full(g_direct_hash, g_direct_equal, NULL, display_stream_destroy);
>      c->image_cache.ops = &image_cache_ops;
>      c->palette_cache.ops = &palette_cache_ops;
>      c->image_surfaces.ops = &image_surfaces_ops;
> @@ -1207,15 +1207,18 @@ static void report_invalid_stream(SpiceChannel *channel, uint32_t id)
>  
>  static display_stream *get_stream_by_id(SpiceChannel *channel, uint32_t id)
>  {
> +    display_stream *st;
>      SpiceDisplayChannelPrivate *c = SPICE_DISPLAY_CHANNEL(channel)->priv;
>  
> -    if (c != NULL && c->streams != NULL && id < c->nstreams &&
> -        c->streams[id] != NULL) {
> -        return c->streams[id];
> +    g_return_val_if_fail(c != NULL && c->streams != NULL, NULL);
> +
> +    st = g_hash_table_lookup(c->streams, GUINT_TO_POINTER(id));
> +    if (st == NULL) {
> +        spice_printerr("couldn't find stream %u", id);
> +        report_invalid_stream(channel, id);
>      }
>  
> -    report_invalid_stream(channel, id);
> -    return NULL;
> +    return st;
>  }

I haven't studied the code a whole lot, but this looks to be on the hot
path of receiving every frame. The complexity is constant in both old
and new version, but the hash function has a higher constant. I don't
expect the constant to be significant in comparison to the context, but
do you have any guesstimations and/or numbers? And do we want to rely
on guesstimations or want numbers here?

Might be a non-issue, just pointing it out as probably the only real
consideration with this patch?

>  
>  /* coroutine context */
> @@ -1257,45 +1260,36 @@ static display_stream *display_stream_create(SpiceChannel *channel,
>      return st;
>  }
>  
> -static void destroy_stream(SpiceChannel *channel, int id)
> +static void destroy_stream(SpiceChannel *channel, uint32_t id)
>  {
>      SpiceDisplayChannelPrivate *c = SPICE_DISPLAY_CHANNEL(channel)->priv;
>  
>      g_return_if_fail(c != NULL);
>      g_return_if_fail(c->streams != NULL);
> -    g_return_if_fail(c->nstreams > id);
>  
> -    g_clear_pointer(&c->streams[id], display_stream_destroy);
> +    g_hash_table_remove(c->streams, GUINT_TO_POINTER(id));
>  }
>  
>  static void display_handle_stream_create(SpiceChannel *channel, SpiceMsgIn *in)
>  {
>      SpiceDisplayChannelPrivate *c = SPICE_DISPLAY_CHANNEL(channel)->priv;
>      SpiceMsgDisplayStreamCreate *op = spice_msg_in_parsed(in);
> +    display_stream *st;
>  
>      CHANNEL_DEBUG(channel, "%s: id %u", __FUNCTION__, op->id);
> +    g_return_if_fail(c->streams != NULL);
>  
> -    if (op->id >= c->nstreams) {
> -        int n = c->nstreams;
> -        if (!c->nstreams) {
> -            c->nstreams = 1;
> -        }
> -        while (op->id >= c->nstreams) {
> -            c->nstreams *= 2;
> -        }
> -        c->streams = realloc(c->streams, c->nstreams * sizeof(c->streams[0]));
> -        memset(c->streams + n, 0, (c->nstreams - n) * sizeof(c->streams[0]));
> -    }
> -    g_return_if_fail(c->streams[op->id] == NULL);
> -
> -    c->streams[op->id] = display_stream_create(channel, op->id, op->surface_id,
> -                                               op->flags, op->codec_type,
> -                                               &op->dest, &op->clip);
> -    if (c->streams[op->id] == NULL) {
> +    st = display_stream_create(channel, op->id, op->surface_id,
> +                               op->flags, op->codec_type,
> +                               &op->dest, &op->clip);
> +    if (st == NULL) {
>          spice_printerr("could not create the %u video stream", op->id);
>          destroy_stream(channel, op->id);
>          report_invalid_stream(channel, op->id);
> +        return;
>      }
> +
> +    g_hash_table_insert(c->streams, GUINT_TO_POINTER(op->id), st);
>  }
>  
>  static const SpiceRect *stream_get_dest(display_stream *st, SpiceMsgIn *frame_msg)
> @@ -1470,18 +1464,21 @@ static void display_session_mm_time_reset_cb(SpiceSession *session, gpointer dat
>  {
>      SpiceChannel *channel = data;
>      SpiceDisplayChannelPrivate *c = SPICE_DISPLAY_CHANNEL(channel)->priv;
> -    guint i;
> +    GHashTableIter iter;
> +    gpointer key, value;
>  
>      CHANNEL_DEBUG(channel, "%s", __FUNCTION__);
>  
> -    for (i = 0; i < c->nstreams; i++) {
> -        display_stream *st;
> +    g_hash_table_iter_init (&iter, c->streams);
> +    while (g_hash_table_iter_next (&iter, &key, &value)) {
> +        display_stream *st = value;
>  
> -        if (c->streams[i] == NULL) {
> +        if (st == NULL) {
> +            g_warn_if_reached();
>              continue;
>          }
> -        SPICE_DEBUG("%s: stream-id %u", __FUNCTION__, i);
> -        st = c->streams[i];
> +
> +        SPICE_DEBUG("%s: stream-id %u", __FUNCTION__, GPOINTER_TO_UINT(key));
>          st->video_decoder->reschedule(st->video_decoder);
>      }
>  }
> @@ -1626,13 +1623,7 @@ static void display_stream_destroy(gpointer st_pointer)
>  static void clear_streams(SpiceChannel *channel)
>  {
>      SpiceDisplayChannelPrivate *c = SPICE_DISPLAY_CHANNEL(channel)->priv;
> -    int i;
> -
> -    for (i = 0; i < c->nstreams; i++) {
> -        destroy_stream(channel, i);
> -    }
> -    g_clear_pointer(&c->streams, g_free);
> -    c->nstreams = 0;
> +    g_hash_table_remove_all(c->streams);
>  }
>  
>  /* coroutine context */