gstreamer/gst/gstcontext.c
Mathieu Duponchelle 45d11f6590 docs: standardize GstContext, GstControlBinding documentation
* Document virtual methods in standalone comments, in order to properly
  annotate them

* Don't repeat what annotations are stating with respect to ownership
  transfer, nullability

* Mark GstControlBinding ABI field as private

* Misc cleanup / typo fixes / addition of links

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/758>
2021-02-15 15:27:14 +01:00

362 lines
9.8 KiB
C

/* GStreamer
* Copyright (C) 2013 Collabora Ltd.
* Author: Sebastian Dröge <sebastian.droege@collabora.co.uk>
* Copyright (C) 2013 Sebastian Dröge <slomo@circular-chaos.org>
*
* gstcontext.h: Header for GstContext subsystem
*
* 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 St, Fifth Floor,
* Boston, MA 02110-1301, USA.
*/
/**
* SECTION:gstcontext
* @title: GstContext
* @short_description: Lightweight objects to represent element contexts
* @see_also: #GstMiniObject, #GstElement
*
* #GstContext is a container object used to store contexts like a device
* context, a display server connection and similar concepts that should
* be shared between multiple elements.
*
* Applications can set a context on a complete pipeline by using
* gst_element_set_context(), which will then be propagated to all
* child elements. Elements can handle these in #GstElementClass::set_context
* and merge them with the context information they already have.
*
* When an element needs a context it will do the following actions in this
* order until one step succeeds:
*
* 1. Check if the element already has a context
* 2. Query downstream with %GST_QUERY_CONTEXT for the context
* 3. Query upstream with %GST_QUERY_CONTEXT for the context
* 4. Post a %GST_MESSAGE_NEED_CONTEXT message on the bus with the required
* context types and afterwards check if a usable context was set now
* 5. Create a context by itself and post a %GST_MESSAGE_HAVE_CONTEXT message
* on the bus.
*
* Bins will catch %GST_MESSAGE_NEED_CONTEXT messages and will set any previously
* known context on the element that asks for it if possible. Otherwise the
* application should provide one if it can.
*
* #GstContext can be persistent.
* A persistent #GstContext is kept in elements when they reach
* %GST_STATE_NULL, non-persistent ones will be removed.
* Also, a non-persistent context won't override a previous persistent
* context set to an element.
*
* Since: 1.2
*/
#define GST_DISABLE_MINIOBJECT_INLINE_FUNCTIONS
#include "gst_private.h"
#include <string.h>
#include "gstcontext.h"
#include "gstquark.h"
struct _GstContext
{
GstMiniObject mini_object;
gchar *context_type;
GstStructure *structure;
gboolean persistent;
};
#define GST_CONTEXT_STRUCTURE(c) (((GstContext *)(c))->structure)
GType _gst_context_type = 0;
GST_DEFINE_MINI_OBJECT_TYPE (GstContext, gst_context);
void
_priv_gst_context_initialize (void)
{
GST_CAT_INFO (GST_CAT_GST_INIT, "init contexts");
/* the GstMiniObject types need to be class_ref'd once before it can be
* done from multiple threads;
* see http://bugzilla.gnome.org/show_bug.cgi?id=304551 */
gst_context_get_type ();
_gst_context_type = gst_context_get_type ();
}
static void
_gst_context_free (GstContext * context)
{
GstStructure *structure;
g_return_if_fail (context != NULL);
GST_CAT_LOG (GST_CAT_CONTEXT, "finalize context %p: %" GST_PTR_FORMAT,
context, GST_CONTEXT_STRUCTURE (context));
structure = GST_CONTEXT_STRUCTURE (context);
if (structure) {
gst_structure_set_parent_refcount (structure, NULL);
gst_structure_free (structure);
}
g_free (context->context_type);
#ifdef USE_POISONING
memset (context, 0xff, sizeof (GstContext));
#endif
g_slice_free1 (sizeof (GstContext), context);
}
static void gst_context_init (GstContext * context);
static GstContext *
_gst_context_copy (GstContext * context)
{
GstContext *copy;
GstStructure *structure;
GST_CAT_LOG (GST_CAT_CONTEXT, "copy context %p: %" GST_PTR_FORMAT, context,
GST_CONTEXT_STRUCTURE (context));
copy = g_slice_new0 (GstContext);
gst_context_init (copy);
copy->context_type = g_strdup (context->context_type);
structure = GST_CONTEXT_STRUCTURE (context);
GST_CONTEXT_STRUCTURE (copy) = gst_structure_copy (structure);
gst_structure_set_parent_refcount (GST_CONTEXT_STRUCTURE (copy),
&copy->mini_object.refcount);
copy->persistent = context->persistent;
return GST_CONTEXT_CAST (copy);
}
static void
gst_context_init (GstContext * context)
{
gst_mini_object_init (GST_MINI_OBJECT_CAST (context), 0, _gst_context_type,
(GstMiniObjectCopyFunction) _gst_context_copy, NULL,
(GstMiniObjectFreeFunction) _gst_context_free);
}
/**
* gst_context_new:
* @context_type: Context type
* @persistent: Persistent context
*
* Creates a new context.
*
* Returns: (transfer full): The new context.
*
* Since: 1.2
*/
GstContext *
gst_context_new (const gchar * context_type, gboolean persistent)
{
GstContext *context;
GstStructure *structure;
g_return_val_if_fail (context_type != NULL, NULL);
context = g_slice_new0 (GstContext);
GST_CAT_LOG (GST_CAT_CONTEXT, "creating new context %p", context);
structure = gst_structure_new_id_empty (GST_QUARK (CONTEXT));
gst_structure_set_parent_refcount (structure, &context->mini_object.refcount);
gst_context_init (context);
context->context_type = g_strdup (context_type);
GST_CONTEXT_STRUCTURE (context) = structure;
context->persistent = persistent;
return context;
}
/**
* gst_context_get_context_type:
* @context: The #GstContext.
*
* Gets the type of @context.
*
* Returns: The type of the context.
*
* Since: 1.2
*/
const gchar *
gst_context_get_context_type (const GstContext * context)
{
g_return_val_if_fail (GST_IS_CONTEXT (context), NULL);
return context->context_type;
}
/**
* gst_context_has_context_type:
* @context: The #GstContext.
* @context_type: Context type to check.
*
* Checks if @context has @context_type.
*
* Returns: %TRUE if @context has @context_type.
*
* Since: 1.2
*/
gboolean
gst_context_has_context_type (const GstContext * context,
const gchar * context_type)
{
g_return_val_if_fail (GST_IS_CONTEXT (context), FALSE);
g_return_val_if_fail (context_type != NULL, FALSE);
return strcmp (context->context_type, context_type) == 0;
}
/**
* gst_context_get_structure:
* @context: The #GstContext.
*
* Accesses the structure of the context.
*
* Returns: (transfer none): The structure of the context. The structure is
* still owned by the context, which means that you should not modify it,
* free it and that the pointer becomes invalid when you free the context.
*
* Since: 1.2
*/
const GstStructure *
gst_context_get_structure (const GstContext * context)
{
g_return_val_if_fail (GST_IS_CONTEXT (context), NULL);
return GST_CONTEXT_STRUCTURE (context);
}
/**
* gst_context_writable_structure:
* @context: The #GstContext.
*
* Gets a writable version of the structure.
*
* Returns: The structure of the context. The structure is still
* owned by the context, which means that you should not free it and
* that the pointer becomes invalid when you free the context.
* This function checks if @context is writable.
*
* Since: 1.2
*/
GstStructure *
gst_context_writable_structure (GstContext * context)
{
g_return_val_if_fail (GST_IS_CONTEXT (context), NULL);
g_return_val_if_fail (gst_context_is_writable (context), NULL);
return GST_CONTEXT_STRUCTURE (context);
}
/**
* gst_context_is_persistent:
* @context: The #GstContext.
*
* Checks if @context is persistent.
*
* Returns: %TRUE if the context is persistent.
*
* Since: 1.2
*/
gboolean
gst_context_is_persistent (const GstContext * context)
{
g_return_val_if_fail (GST_IS_CONTEXT (context), FALSE);
return context->persistent;
}
/**
* gst_context_ref:
* @context: the context to ref
*
* Convenience macro to increase the reference count of the context.
*
* Returns: @context (for convenience when doing assignments)
*
* Since: 1.2
*/
GstContext *
gst_context_ref (GstContext * context)
{
return (GstContext *) gst_mini_object_ref (GST_MINI_OBJECT_CAST (context));
}
/**
* gst_context_unref:
* @context: the context to unref
*
* Convenience macro to decrease the reference count of the context, possibly
* freeing it.
*
* Since: 1.2
*/
void
gst_context_unref (GstContext * context)
{
gst_mini_object_unref (GST_MINI_OBJECT_CAST (context));
}
/**
* gst_context_copy:
* @context: the context to copy
*
* Creates a copy of the context. Returns a copy of the context.
*
* Returns: (transfer full): a new copy of @context.
*
* MT safe
*
* Since: 1.2
*/
GstContext *
gst_context_copy (const GstContext * context)
{
return
GST_CONTEXT_CAST (gst_mini_object_copy (GST_MINI_OBJECT_CONST_CAST
(context)));
}
/**
* gst_context_replace:
* @old_context: (inout) (transfer full): pointer to a pointer to a #GstContext
* to be replaced.
* @new_context: (allow-none) (transfer none): pointer to a #GstContext that will
* replace the context pointed to by @old_context.
*
* Modifies a pointer to a #GstContext to point to a different #GstContext. The
* modification is done atomically (so this is useful for ensuring thread safety
* in some cases), and the reference counts are updated appropriately (the old
* context is unreffed, the new one is reffed).
*
* Either @new_context or the #GstContext pointed to by @old_context may be %NULL.
*
* Returns: %TRUE if @new_context was different from @old_context
*
* Since: 1.2
*/
gboolean
gst_context_replace (GstContext ** old_context, GstContext * new_context)
{
return gst_mini_object_replace ((GstMiniObject **) old_context,
(GstMiniObject *) new_context);
}