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/* GStreamer Wayland video sink
* Copyright (C) 2014 Collabora Ltd.
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* Library General Public License for more details.
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the Free
* Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301 USA.
/* GstWlBuffer wraps wl_buffer and provides a mechanism for preventing
* buffers from being re-used while the compositor is using them. This
* is achieved by adding a reference to the GstBuffer as soon as its
* associated wl_buffer is sent to the compositor and by removing this
* reference as soon as the compositor sends a wl_buffer::release message.
* This mechanism is a bit complicated, though, because it adds cyclic
* references that can be dangerous. The reference cycles looks like:
* ----------------
* | GstWlDisplay | ---------------------------->
* ---------------- |
* |
* V
* ----------------- ------------- ---------------
* | GstBufferPool | --> | GstBuffer | ==> | GstWlBuffer |
* | | <-- | | <-- | |
* ----------------- ------------- ---------------
* A GstBufferPool normally holds references to its GstBuffers and each buffer
* holds a reference to a GstWlBuffer (saved in the GstMiniObject qdata).
* When a GstBuffer is in use, it holds a reference back to the pool and the
* pool doesn't hold a reference to the GstBuffer. When the GstBuffer is unrefed
* externally, it returns back to the pool and the pool holds again a reference
* to the buffer.
* Now when the compositor is using a buffer, the GstWlBuffer also holds a ref
* to the GstBuffer, which prevents it from returning to the pool. When the
* last GstWlBuffer receives a release event and unrefs the last GstBuffer,
* the GstBufferPool will be able to stop and if no-one is holding a strong
* ref to it, it will be destroyed. This will destroy the pool's GstBuffers and
* also the GstWlBuffers. This will all happen in the same context of the last
* gst_buffer_unref, which will be called from the buffer_release() callback.
* The problem here lies in the fact that buffer_release() will be called
* from the event loop thread of GstWlDisplay, so it's as if the display
* holds a reference to the GstWlBuffer, but without having an actual reference.
* When we kill the display, there is no way for the GstWlBuffer, the associated
* GstBuffer and the GstBufferPool to get destroyed, so we are going to leak a
* fair ammount of memory.
* Normally, this rarely happens, because the compositor releases buffers
* almost immediately and when waylandsink stops, they are already released.
* However, we want to be absolutely certain, so a solution is introduced
* by registering all the GstWlBuffers with the display and explicitly
* releasing all the buffer references as soon as the display is destroyed.
* When the GstWlDisplay is finalized, it takes a reference to all the
* registered GstWlBuffers and then calls gst_wl_buffer_force_release_and_unref,
* which releases the potential reference to the GstBuffer, destroys the
* underlying wl_buffer and removes the reference that GstWlDisplay is holding.
* At that point, either the GstBuffer is alive somewhere and still holds a ref
* to the GstWlBuffer, which it will release when it gets destroyed, or the
* GstBuffer was destroyed in the meantime and the GstWlBuffer gets destroyed
* as soon as we remove the reference that GstWlDisplay holds.
#include "wlbuffer.h"
GST_DEBUG_CATEGORY_EXTERN (gstwayland_debug);
#define GST_CAT_DEFAULT gstwayland_debug
G_DEFINE_TYPE (GstWlBuffer, gst_wl_buffer, G_TYPE_OBJECT);
static G_DEFINE_QUARK (GstWlBufferQDataQuark, gst_wl_buffer_qdata);
static void
gst_wl_buffer_dispose (GObject * gobject)
GstWlBuffer *self = GST_WL_BUFFER (gobject);
GST_TRACE_OBJECT (self, "dispose");
/* if the display is shutting down and we are trying to dipose
* the GstWlBuffer from another thread, unregister_buffer() will
* block and in the end the display will increase the refcount
* of this GstWlBuffer, so it will not be finalized */
if (self->display)
gst_wl_display_unregister_buffer (self->display, self);
G_OBJECT_CLASS (gst_wl_buffer_parent_class)->dispose (gobject);
static void
gst_wl_buffer_finalize (GObject * gobject)
GstWlBuffer *self = GST_WL_BUFFER (gobject);
GST_TRACE_OBJECT (self, "finalize");
if (self->wlbuffer)
wl_buffer_destroy (self->wlbuffer);
G_OBJECT_CLASS (gst_wl_buffer_parent_class)->finalize (gobject);
static void
gst_wl_buffer_class_init (GstWlBufferClass * klass)
GObjectClass *object_class = (GObjectClass *) klass;
object_class->dispose = gst_wl_buffer_dispose;
object_class->finalize = gst_wl_buffer_finalize;
static void
gst_wl_buffer_init (GstWlBuffer * self)
static void
buffer_release (void *data, struct wl_buffer *wl_buffer)
GstWlBuffer *self = data;
GST_LOG_OBJECT (self, "wl_buffer::release (GstBuffer: %p)", self->gstbuffer);
self->used_by_compositor = FALSE;
/* unref should be last, because it may end up destroying the GstWlBuffer */
gst_buffer_unref (self->gstbuffer);
static const struct wl_buffer_listener buffer_listener = {
static void
gstbuffer_disposed (GstWlBuffer * self)
g_assert (!self->used_by_compositor);
self->gstbuffer = NULL;
GST_TRACE_OBJECT (self, "owning GstBuffer was finalized");
/* this will normally destroy the GstWlBuffer, unless the display is
* finalizing and it has taken an additional reference to it */
g_object_unref (self);
GstWlBuffer *
gst_buffer_add_wl_buffer (GstBuffer * gstbuffer, struct wl_buffer *wlbuffer,
GstWlDisplay * display)
GstWlBuffer *self;
self = g_object_new (GST_TYPE_WL_BUFFER, NULL);
self->gstbuffer = gstbuffer;
self->wlbuffer = wlbuffer;
self->display = display;
gst_wl_display_register_buffer (self->display, self);
wl_buffer_add_listener (self->wlbuffer, &buffer_listener, self);
gst_mini_object_set_qdata ((GstMiniObject *) gstbuffer,
gst_wl_buffer_qdata_quark (), self, (GDestroyNotify) gstbuffer_disposed);
return self;
GstWlBuffer *
gst_buffer_get_wl_buffer (GstBuffer * gstbuffer)
return gst_mini_object_get_qdata ((GstMiniObject *) gstbuffer,
gst_wl_buffer_qdata_quark ());
gst_wl_buffer_force_release_and_unref (GstWlBuffer * self)
/* Force a buffer release.
* At this point, the GstWlDisplay has killed its event loop,
* so we don't need to worry about buffer_release() being called
* at the same time from the event loop thread */
if (self->used_by_compositor) {
GST_DEBUG_OBJECT (self, "forcing wl_buffer::release (GstBuffer: %p)",
self->used_by_compositor = FALSE;
gst_buffer_unref (self->gstbuffer);
/* Finalize this GstWlBuffer early.
* This method has been called as a result of the display shutting down,
* so we need to stop using any wayland resources and disconnect from
* the display. The GstWlBuffer stays alive, though, to avoid race
* conditions with the GstBuffer being destroyed from another thread.
* The last reference is either owned by the GstBuffer or by us and
* it will be released at the end of this function. */
GST_TRACE_OBJECT (self, "finalizing early");
wl_buffer_destroy (self->wlbuffer);
self->wlbuffer = NULL;
self->display = NULL;
/* remove the reference that the caller (GstWlDisplay) owns */
g_object_unref (self);
gst_wl_buffer_attach (GstWlBuffer * self, struct wl_surface *surface)
g_return_if_fail (self->used_by_compositor == FALSE);
wl_surface_attach (surface, self->wlbuffer, 0, 0);
/* Add a reference to the buffer. This represents the fact that
* the compositor is using the buffer and it should not return
* back to the pool and be re-used until the compositor releases it. */
gst_buffer_ref (self->gstbuffer);
self->used_by_compositor = TRUE;