Problem with GstQueryAllocation pool refcount

[Nicolas Dufresne]

Le mardi 06 décembre 2022 à 09:31 +0000, Edgar Thier via gstreamer-devel a
écrit :
> Hi,
> 
> I am encountering a problem with the reference count for my custom
> GstBufferPool.
> What I am observing is that GstQuery increases the reference count but never
> seems to unref it.
> 
> My allocation function looks like this (simplified):
> 
> gboolean _device_allocation(GstBaseSrc* base_src, GstQuery* query)

s/_device_allocation/_decide_allocation/

> {
>     // my_buffer_pool_new does:
>     // GstTcamBufferPool* pool =
>     //     (GstTcamBufferPool*)g_object_new(GST_TYPE_MY_BUFFER_POOL, "name",
> name, NULL);
>     // g_object_ref_sink(pool);
>     GstBufferPool* pool = my_buffer_pool_new(GST_ELEMENT(self), caps);
>     GST_ERROR("Refcount: %d", pool->object.object.ref_count);
>     // Refcount: 1
>     GstStructure* config = gst_buffer_pool_get_config(pool);
> 
>     gst_buffer_pool_config_set_params(config, caps, buffer_size, 10, 10);
>     gst_buffer_pool_set_config(pool, config);
>     gst_query_add_allocation_pool(query, pool, size, 10, 0);

      gst_object_unref (pool);

This is because the method to store a pool in the query is not a
"transfer:floating" method. From the doc, you can see "transfer: none"
annotation.

> pool ( [transfer: none][allow-none]) – the GstBufferPool

> 
>     GST_ERROR("Refcount: %d", pool->object.object.ref_count);
>     // Refcount: 2
> 
>     // store pool pointer for later cleanup
>     ...
> 
>     return GST_BASE_SRC_CLASS(gst_tcam_mainsrc_parent_class)-
> >decide_allocation(base_src, query);
> }
> 
> It remains at two even when I reach state change paused->ready where I want to
> reset the pool:
> 
> _change_state(GstElement* element,
>               GstStateChange change)
> {
> ....
> case GST_STATE_CHANGE_PAUSED_TO_READY:
> {
>     GstBufferPool* pool = ...;
>     if (pool)
>     {
>         gst_buffer_pool_set_active(pool, FALSE);
>         GST_ERROR("Freeing pool %d", pool->object.object.ref_count);
>         // Refcount: 2
>         gst_object_unref(pool);
> 
>         pool = NULL;
>         // BufferPool not freed
>     }
> ...
> 
> 
> Am I doing something wrong?
> Do I need to execute additional steps or is this a bug with GstQuery?
> 
> Thanks,
> 
> Edgar
>