gstreamer/subprojects/gst-plugins-bad/gst-libs/gst/wayland/gstwlbuffer.c

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/* GStreamer Wayland Library
*
* 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
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* 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 weak ref data).
* 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
2019-09-02 19:08:44 +00:00
* fair amount 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.
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "gstwlbuffer.h"
#define GST_CAT_DEFAULT gst_wl_buffer_debug
GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
typedef struct _GstWlBufferPrivate
{
struct wl_buffer *wlbuffer;
GstBuffer *current_gstbuffer;
GstMemory *gstmem;
GstWlDisplay *display;
gboolean used_by_compositor;
} GstWlBufferPrivate;
G_DEFINE_TYPE_WITH_CODE (GstWlBuffer, gst_wl_buffer, G_TYPE_OBJECT,
G_ADD_PRIVATE (GstWlBuffer)
GST_DEBUG_CATEGORY_INIT (gst_wl_buffer_debug,
"wlbuffer", 0, "wlbuffer library");
);
static void
gst_wl_buffer_dispose (GObject * gobject)
{
GstWlBuffer *self = GST_WL_BUFFER (gobject);
GstWlBufferPrivate *priv = gst_wl_buffer_get_instance_private (self);
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 (priv->display) {
gst_wl_display_unregister_buffer (priv->display, priv->gstmem);
}
G_OBJECT_CLASS (gst_wl_buffer_parent_class)->dispose (gobject);
}
static void
gst_wl_buffer_finalize (GObject * gobject)
{
GstWlBuffer *self = GST_WL_BUFFER (gobject);
GstWlBufferPrivate *priv = gst_wl_buffer_get_instance_private (self);
GST_TRACE_OBJECT (self, "finalize");
if (priv->wlbuffer)
wl_buffer_destroy (priv->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;
GstWlBufferPrivate *priv = gst_wl_buffer_get_instance_private (self);
GstBuffer *buf = priv->current_gstbuffer;
GST_LOG_OBJECT (self, "wl_buffer::release (GstBuffer: %p)", buf);
priv->used_by_compositor = FALSE;
priv->current_gstbuffer = NULL;
/* unref should be last, because it may end up destroying the GstWlBuffer */
gst_buffer_unref (buf);
}
static const struct wl_buffer_listener buffer_listener = {
buffer_release
};
static void
gstmemory_disposed (GstWlBuffer * self)
{
GstWlBufferPrivate *priv = gst_wl_buffer_get_instance_private (self);
g_assert (!priv->used_by_compositor);
GST_TRACE_OBJECT (self, "owning GstMemory 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;
GstWlBufferPrivate *priv;
self = g_object_new (GST_TYPE_WL_BUFFER, NULL);
priv = gst_wl_buffer_get_instance_private (self);
priv->current_gstbuffer = gstbuffer;
priv->wlbuffer = wlbuffer;
priv->display = display;
priv->gstmem = gst_buffer_peek_memory (gstbuffer, 0);
gst_wl_display_register_buffer (priv->display, priv->gstmem, self);
wl_buffer_add_listener (priv->wlbuffer, &buffer_listener, self);
gst_mini_object_weak_ref (GST_MINI_OBJECT (priv->gstmem),
(GstMiniObjectNotify) gstmemory_disposed, self);
return self;
}
GstWlBuffer *
gst_buffer_get_wl_buffer (GstWlDisplay * display, GstBuffer * gstbuffer)
{
GstMemory *mem0;
GstWlBuffer *wlbuf;
if (!gstbuffer)
return NULL;
mem0 = gst_buffer_peek_memory (gstbuffer, 0);
wlbuf = gst_wl_display_lookup_buffer (display, mem0);
if (wlbuf) {
GstWlBufferPrivate *priv = gst_wl_buffer_get_instance_private (wlbuf);
priv->current_gstbuffer = gstbuffer;
}
return wlbuf;
}
void
gst_wl_buffer_force_release_and_unref (GstBuffer * buf, GstWlBuffer * self)
{
GstWlBufferPrivate *priv = gst_wl_buffer_get_instance_private (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 (priv->used_by_compositor) {
GST_DEBUG_OBJECT (self, "forcing wl_buffer::release (GstBuffer: %p)",
priv->current_gstbuffer);
priv->used_by_compositor = FALSE;
gst_buffer_unref (priv->current_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 (priv->wlbuffer);
priv->wlbuffer = NULL;
priv->display = NULL;
priv->current_gstbuffer = NULL;
/* remove the reference that the caller (GstWlDisplay) owns */
g_object_unref (self);
}
void
gst_wl_buffer_attach (GstWlBuffer * self, struct wl_surface *surface)
{
GstWlBufferPrivate *priv = gst_wl_buffer_get_instance_private (self);
if (priv->used_by_compositor) {
GST_DEBUG_OBJECT (self, "buffer used by compositor %p",
priv->current_gstbuffer);
return;
}
wl_surface_attach (surface, priv->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 (priv->current_gstbuffer);
priv->used_by_compositor = TRUE;
}
GstWlDisplay *
gst_wl_buffer_get_display (GstWlBuffer * self)
{
GstWlBufferPrivate *priv = gst_wl_buffer_get_instance_private (self);
return priv->display;
}