gstreamer/gst/gstpromise.c

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/* GStreamer
* Copyright (C) 2017 Matthew Waters <matthew@centricular.com>
*
* 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.
*/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#define GST_DISABLE_MINIOBJECT_INLINE_FUNCTIONS
#include "gst_private.h"
#include "gstpromise.h"
#define GST_CAT_DEFAULT gst_promise_debug
GST_DEBUG_CATEGORY_STATIC (GST_CAT_DEFAULT);
/**
* SECTION:gstpromise
* @title: GstPromise
* @short_description: a miniobject for future/promise-like functionality
*
* The #GstPromise object implements the container for values that may
* be available later. i.e. a Future or a Promise in
* <https://en.wikipedia.org/wiki/Futures_and_promises>.
* As with all Future/Promise-like functionality, there is the concept of the
* producer of the value and the consumer of the value.
*
* A #GstPromise is created with gst_promise_new() by the consumer and passed
* to the producer to avoid thread safety issues with the change callback.
* A #GstPromise can be replied to with a value (or an error) by the producer
* with gst_promise_reply(). The exact value returned is defined by the API
* contract of the producer and %NULL may be a valid reply.
* gst_promise_interrupt() is for the consumer to
* indicate to the producer that the value is not needed anymore and producing
* that value can stop. The @GST_PROMISE_RESULT_EXPIRED state set by a call
* to gst_promise_expire() indicates to the consumer that a value will never
* be produced and is intended to be called by a third party that implements
* some notion of message handling such as #GstBus.
* A callback can also be installed at #GstPromise creation for
* result changes with gst_promise_new_with_change_func().
* The change callback can be used to chain #GstPromises's together as in the
* following example.
* |[<!-- language="C" -->
* const GstStructure *reply;
* GstPromise *p;
* if (gst_promise_wait (promise) != GST_PROMISE_RESULT_REPLIED)
* return; // interrupted or expired value
* reply = gst_promise_get_reply (promise);
* if (error in reply)
* return; // propagate error
* p = gst_promise_new_with_change_func (another_promise_change_func, user_data, notify);
* pass p to promise-using API
* ]|
*
* Each #GstPromise starts out with a #GstPromiseResult of
* %GST_PROMISE_RESULT_PENDING and only ever transitions once
* into one of the other #GstPromiseResult's.
*
* In order to support multi-threaded code, gst_promise_reply(),
* gst_promise_interrupt() and gst_promise_expire() may all be from
* different threads with some restrictions and the final result of the promise
* is whichever call is made first. There are two restrictions on ordering:
*
* 1. That gst_promise_reply() and gst_promise_interrupt() cannot be called
* after gst_promise_expire()
* 2. That gst_promise_reply() and gst_promise_interrupt()
* cannot be called twice.
*
* The change function set with gst_promise_new_with_change_func() is
* called directly from either the gst_promise_reply(),
* gst_promise_interrupt() or gst_promise_expire() and can be called
* from an arbitrary thread. #GstPromise using APIs can restrict this to
* a single thread or a subset of threads but that is entirely up to the API
* that uses #GstPromise.
*/
static const int immutable_structure_refcount = 2;
#define GST_PROMISE_REPLY(p) (((GstPromiseImpl *)(p))->reply)
#define GST_PROMISE_RESULT(p) (((GstPromiseImpl *)(p))->result)
#define GST_PROMISE_LOCK(p) (&(((GstPromiseImpl *)(p))->lock))
#define GST_PROMISE_COND(p) (&(((GstPromiseImpl *)(p))->cond))
#define GST_PROMISE_CHANGE_FUNC(p) (((GstPromiseImpl *)(p))->change_func)
#define GST_PROMISE_CHANGE_DATA(p) (((GstPromiseImpl *)(p))->user_data)
#define GST_PROMISE_CHANGE_NOTIFY(p) (((GstPromiseImpl *)(p))->notify)
typedef struct
{
GstPromise promise;
GstPromiseResult result;
GstStructure *reply;
GMutex lock;
GCond cond;
GstPromiseChangeFunc change_func;
gpointer user_data;
GDestroyNotify notify;
} GstPromiseImpl;
/**
* gst_promise_wait:
* @promise: a #GstPromise
*
* Wait for @promise to move out of the %GST_PROMISE_RESULT_PENDING state.
* If @promise is not in %GST_PROMISE_RESULT_PENDING then it will return
* immediately with the current result.
*
* Returns: the result of the promise
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*
* Since: 1.14
*/
GstPromiseResult
gst_promise_wait (GstPromise * promise)
{
GstPromiseResult ret;
g_return_val_if_fail (promise != NULL, GST_PROMISE_RESULT_EXPIRED);
g_mutex_lock (GST_PROMISE_LOCK (promise));
ret = GST_PROMISE_RESULT (promise);
while (ret == GST_PROMISE_RESULT_PENDING) {
GST_LOG ("%p waiting", promise);
g_cond_wait (GST_PROMISE_COND (promise), GST_PROMISE_LOCK (promise));
ret = GST_PROMISE_RESULT (promise);
}
GST_LOG ("%p waited", promise);
g_mutex_unlock (GST_PROMISE_LOCK (promise));
return ret;
}
/**
* gst_promise_reply:
* @promise: (allow-none): a #GstPromise
* @s: (transfer full) (nullable): a #GstStructure with the the reply contents
*
* Set a reply on @promise. This will wake up any waiters with
* %GST_PROMISE_RESULT_REPLIED. Called by the producer of the value to
* indicate success (or failure).
*
* If @promise has already been interrupted by the consumer, then this reply
* is not visible to the consumer.
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*
* Since: 1.14
*/
void
gst_promise_reply (GstPromise * promise, GstStructure * s)
{
GstPromiseChangeFunc change_func = NULL;
gpointer change_data = NULL;
/* Caller requested that no reply is necessary */
if (promise == NULL)
return;
g_mutex_lock (GST_PROMISE_LOCK (promise));
if (GST_PROMISE_RESULT (promise) != GST_PROMISE_RESULT_PENDING &&
GST_PROMISE_RESULT (promise) != GST_PROMISE_RESULT_INTERRUPTED) {
GstPromiseResult result = GST_PROMISE_RESULT (promise);
g_mutex_unlock (GST_PROMISE_LOCK (promise));
g_return_if_fail (result == GST_PROMISE_RESULT_PENDING ||
result == GST_PROMISE_RESULT_INTERRUPTED);
}
/* XXX: is this necessary and valid? */
if (GST_PROMISE_REPLY (promise) && GST_PROMISE_REPLY (promise) != s)
gst_structure_free (GST_PROMISE_REPLY (promise));
/* Only reply iff we are currently in pending */
if (GST_PROMISE_RESULT (promise) == GST_PROMISE_RESULT_PENDING) {
if (s
&& !gst_structure_set_parent_refcount (s,
(int *) &immutable_structure_refcount)) {
g_critical ("Input structure has a parent already!");
g_mutex_unlock (GST_PROMISE_LOCK (promise));
return;
}
GST_PROMISE_RESULT (promise) = GST_PROMISE_RESULT_REPLIED;
GST_LOG ("%p replied", promise);
GST_PROMISE_REPLY (promise) = s;
change_func = GST_PROMISE_CHANGE_FUNC (promise);
change_data = GST_PROMISE_CHANGE_DATA (promise);
} else {
/* eat the value */
if (s)
gst_structure_free (s);
}
g_cond_broadcast (GST_PROMISE_COND (promise));
g_mutex_unlock (GST_PROMISE_LOCK (promise));
if (change_func)
change_func (promise, change_data);
}
/**
* gst_promise_get_reply:
* @promise: a #GstPromise
*
* Retrieve the reply set on @promise. @promise must be in
* %GST_PROMISE_RESULT_REPLIED and the returned structure is owned by @promise
*
* Returns: (transfer none) (nullable): The reply set on @promise
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*
* Since: 1.14
*/
const GstStructure *
gst_promise_get_reply (GstPromise * promise)
{
g_return_val_if_fail (promise != NULL, NULL);
g_mutex_lock (GST_PROMISE_LOCK (promise));
if (GST_PROMISE_RESULT (promise) != GST_PROMISE_RESULT_REPLIED) {
GstPromiseResult result = GST_PROMISE_RESULT (promise);
g_mutex_unlock (GST_PROMISE_LOCK (promise));
g_return_val_if_fail (result == GST_PROMISE_RESULT_REPLIED, NULL);
}
g_mutex_unlock (GST_PROMISE_LOCK (promise));
return GST_PROMISE_REPLY (promise);
}
/**
* gst_promise_interrupt:
* @promise: a #GstPromise
*
* Interrupt waiting for a @promise. This will wake up any waiters with
* %GST_PROMISE_RESULT_INTERRUPTED. Called when the consumer does not want
* the value produced anymore.
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*
* Since: 1.14
*/
void
gst_promise_interrupt (GstPromise * promise)
{
GstPromiseChangeFunc change_func = NULL;
gpointer change_data = NULL;
g_return_if_fail (promise != NULL);
g_mutex_lock (GST_PROMISE_LOCK (promise));
if (GST_PROMISE_RESULT (promise) != GST_PROMISE_RESULT_PENDING &&
GST_PROMISE_RESULT (promise) != GST_PROMISE_RESULT_REPLIED) {
GstPromiseResult result = GST_PROMISE_RESULT (promise);
g_mutex_unlock (GST_PROMISE_LOCK (promise));
g_return_if_fail (result == GST_PROMISE_RESULT_PENDING ||
result == GST_PROMISE_RESULT_REPLIED);
}
/* only interrupt if we are currently in pending */
if (GST_PROMISE_RESULT (promise) == GST_PROMISE_RESULT_PENDING) {
GST_PROMISE_RESULT (promise) = GST_PROMISE_RESULT_INTERRUPTED;
g_cond_broadcast (GST_PROMISE_COND (promise));
GST_LOG ("%p interrupted", promise);
change_func = GST_PROMISE_CHANGE_FUNC (promise);
change_data = GST_PROMISE_CHANGE_DATA (promise);
}
g_mutex_unlock (GST_PROMISE_LOCK (promise));
if (change_func)
change_func (promise, change_data);
}
/**
* gst_promise_expire:
* @promise: a #GstPromise
*
* Expire a @promise. This will wake up any waiters with
* %GST_PROMISE_RESULT_EXPIRED. Called by a message loop when the parent
* message is handled and/or destroyed (possibly unanswered).
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*
* Since: 1.14
*/
void
gst_promise_expire (GstPromise * promise)
{
GstPromiseChangeFunc change_func = NULL;
gpointer change_data = NULL;
g_return_if_fail (promise != NULL);
g_mutex_lock (GST_PROMISE_LOCK (promise));
if (GST_PROMISE_RESULT (promise) == GST_PROMISE_RESULT_PENDING) {
GST_PROMISE_RESULT (promise) = GST_PROMISE_RESULT_EXPIRED;
g_cond_broadcast (GST_PROMISE_COND (promise));
GST_LOG ("%p expired", promise);
change_func = GST_PROMISE_CHANGE_FUNC (promise);
change_data = GST_PROMISE_CHANGE_DATA (promise);
GST_PROMISE_CHANGE_FUNC (promise) = NULL;
GST_PROMISE_CHANGE_DATA (promise) = NULL;
}
g_mutex_unlock (GST_PROMISE_LOCK (promise));
if (change_func)
change_func (promise, change_data);
}
static void
gst_promise_free (GstMiniObject * object)
{
GstPromise *promise = (GstPromise *) object;
/* the promise *must* be dealt with in some way before destruction */
g_warn_if_fail (GST_PROMISE_RESULT (promise) != GST_PROMISE_RESULT_PENDING);
if (GST_PROMISE_CHANGE_NOTIFY (promise))
GST_PROMISE_CHANGE_NOTIFY (promise) (GST_PROMISE_CHANGE_DATA (promise));
if (GST_PROMISE_REPLY (promise)) {
gst_structure_set_parent_refcount (GST_PROMISE_REPLY (promise), NULL);
gst_structure_free (GST_PROMISE_REPLY (promise));
}
g_mutex_clear (GST_PROMISE_LOCK (promise));
g_cond_clear (GST_PROMISE_COND (promise));
GST_LOG ("%p finalized", promise);
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#ifdef USE_POISONING
memset (promise, 0xff, sizeof (GstPromiseImpl));
#endif
g_free (promise);
}
static void
gst_promise_init (GstPromise * promise)
{
static volatile gsize _init = 0;
if (g_once_init_enter (&_init)) {
GST_DEBUG_CATEGORY_INIT (gst_promise_debug, "gstpromise", 0, "gstpromise");
g_once_init_leave (&_init, 1);
}
gst_mini_object_init (GST_MINI_OBJECT (promise), 0, GST_TYPE_PROMISE, NULL,
NULL, gst_promise_free);
GST_PROMISE_REPLY (promise) = NULL;
GST_PROMISE_RESULT (promise) = GST_PROMISE_RESULT_PENDING;
g_mutex_init (GST_PROMISE_LOCK (promise));
g_cond_init (GST_PROMISE_COND (promise));
}
/**
* gst_promise_new:
*
* Returns: a new #GstPromise
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*
* Since: 1.14
*/
GstPromise *
gst_promise_new (void)
{
GstPromise *promise = GST_PROMISE (g_new0 (GstPromiseImpl, 1));
gst_promise_init (promise);
GST_LOG ("new promise %p", promise);
return promise;
}
/**
* gst_promise_new_with_change_func:
* @func: (scope notified): a #GstPromiseChangeFunc to call
* @user_data: (closure): argument to call @func with
* @notify: notification function that @user_data is no longer needed
*
* @func will be called exactly once when transitioning out of
* %GST_PROMISE_RESULT_PENDING into any of the other #GstPromiseResult
* states.
*
* Returns: a new #GstPromise
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*
* Since: 1.14
*/
GstPromise *
gst_promise_new_with_change_func (GstPromiseChangeFunc func, gpointer user_data,
GDestroyNotify notify)
{
GstPromise *promise = gst_promise_new ();
GST_PROMISE_CHANGE_FUNC (promise) = func;
GST_PROMISE_CHANGE_DATA (promise) = user_data;
GST_PROMISE_CHANGE_NOTIFY (promise) = notify;
return promise;
}
GST_DEFINE_MINI_OBJECT_TYPE (GstPromise, gst_promise);
/**
* gst_promise_ref:
* @promise: a #GstPromise.
*
* Increases the refcount of the given @promise by one.
*
* Returns: (transfer full): @promise
*
* Since: 1.14
*/
GstPromise *
gst_promise_ref (GstPromise * promise)
{
return (GstPromise *) gst_mini_object_ref (GST_MINI_OBJECT_CAST (promise));
}
/**
* gst_promise_unref:
* @promise: (transfer full): a #GstPromise.
*
* Decreases the refcount of the promise. If the refcount reaches 0, the
* promise will be freed.
*
* Since: 1.14
*/
void
gst_promise_unref (GstPromise * promise)
{
gst_mini_object_unref (GST_MINI_OBJECT_CAST (promise));
}