gst/gstatomicqueue.c - mtk-gstreamer-debian - Git at Google

 /* GStreamer
  * Copyright (C) 2009 Edward Hervey <bilboed@bilboed.com>
  *               2011 Wim Taymans <wim.taymans@gmail.com>
  *
  * gstatomicqueue.c:
  *
  * 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.
  */

 #include "gst_private.h"

 #include <string.h>

 #include <gst/gst.h>
 #include "gstatomicqueue.h"
 #include "glib-compat-private.h"

 /**
  * SECTION:gstatomicqueue
  * @title: GstAtomicQueue
  * @short_description: An atomic queue implementation
  *
  * The #GstAtomicQueue object implements a queue that can be used from multiple
  * threads without performing any blocking operations.
  */

 G_DEFINE_BOXED_TYPE (GstAtomicQueue, gst_atomic_queue,
     (GBoxedCopyFunc) gst_atomic_queue_ref,
     (GBoxedFreeFunc) gst_atomic_queue_unref);

 /* By default the queue uses 2 * sizeof(gpointer) * clp2 (max_items) of
  * memory. clp2(x) is the next power of two >= than x.
  *
  * The queue can operate in low memory mode, in which it consumes almost
  * half the memory at the expense of extra overhead in the readers. This
  * is disabled by default because even without LOW_MEM mode, the memory
  * consumption is still lower than a plain GList.
  */
 #undef LOW_MEM

 typedef struct _GstAQueueMem GstAQueueMem;

 struct _GstAQueueMem
 {
   gint size;
   gpointer *array;
   volatile gint head;
   volatile gint tail_write;
   volatile gint tail_read;
   GstAQueueMem *next;
   GstAQueueMem *free;
 };

 static guint
 clp2 (guint n)
 {
   guint res = 1;

   while (res < n)
     res <<= 1;

   return res;
 }

 static GstAQueueMem *
 new_queue_mem (guint size, gint pos)
 {
   GstAQueueMem *mem;

   mem = g_new (GstAQueueMem, 1);

   /* we keep the size as a mask for performance */
   mem->size = clp2 (MAX (size, 16)) - 1;
   mem->array = g_new0 (gpointer, mem->size + 1);
   mem->head = pos;
   mem->tail_write = pos;
   mem->tail_read = pos;
   mem->next = NULL;
   mem->free = NULL;

   return mem;
 }

 static void
 free_queue_mem (GstAQueueMem * mem)
 {
   g_free (mem->array);
   g_free (mem);
 }

 struct _GstAtomicQueue
 {
   volatile gint refcount;
 #ifdef LOW_MEM
   gint num_readers;
 #endif
   GstAQueueMem *head_mem;
   GstAQueueMem *tail_mem;
   GstAQueueMem *free_list;
 };

 static void
 add_to_free_list (GstAtomicQueue * queue, GstAQueueMem * mem)
 {
   do {
     mem->free = g_atomic_pointer_get (&queue->free_list);
   } while (!g_atomic_pointer_compare_and_exchange (&queue->free_list,
           mem->free, mem));
 }

 static void
 clear_free_list (GstAtomicQueue * queue)
 {
   GstAQueueMem *free_list;

   /* take the free list and replace with NULL */
   do {
     free_list = g_atomic_pointer_get (&queue->free_list);
     if (free_list == NULL)
       return;
   } while (!g_atomic_pointer_compare_and_exchange (&queue->free_list, free_list,
           NULL));

   while (free_list) {
     GstAQueueMem *next = free_list->free;

     free_queue_mem (free_list);

     free_list = next;
   }
 }

 /**
  * gst_atomic_queue_new:
  * @initial_size: initial queue size
  *
  * Create a new atomic queue instance. @initial_size will be rounded up to the
  * nearest power of 2 and used as the initial size of the queue.
  *
  * Returns: a new #GstAtomicQueue
  */
 GstAtomicQueue *
 gst_atomic_queue_new (guint initial_size)
 {
   GstAtomicQueue *queue;

   queue = g_new (GstAtomicQueue, 1);

   queue->refcount = 1;
 #ifdef LOW_MEM
   queue->num_readers = 0;
 #endif
   queue->head_mem = queue->tail_mem = new_queue_mem (initial_size, 0);
   queue->free_list = NULL;

   return queue;
 }

 /**
  * gst_atomic_queue_ref:
  * @queue: a #GstAtomicQueue
  *
  * Increase the refcount of @queue.
  */
 void
 gst_atomic_queue_ref (GstAtomicQueue * queue)
 {
   g_return_if_fail (queue != NULL);

   g_atomic_int_inc (&queue->refcount);
 }

 static void
 gst_atomic_queue_free (GstAtomicQueue * queue)
 {
   free_queue_mem (queue->head_mem);
   if (queue->head_mem != queue->tail_mem)
     free_queue_mem (queue->tail_mem);
   clear_free_list (queue);
   g_free (queue);
 }

 /**
  * gst_atomic_queue_unref:
  * @queue: a #GstAtomicQueue
  *
  * Unref @queue and free the memory when the refcount reaches 0.
  */
 void
 gst_atomic_queue_unref (GstAtomicQueue * queue)
 {
   g_return_if_fail (queue != NULL);

   if (g_atomic_int_dec_and_test (&queue->refcount))
     gst_atomic_queue_free (queue);
 }

 /**
  * gst_atomic_queue_peek:
  * @queue: a #GstAtomicQueue
  *
  * Peek the head element of the queue without removing it from the queue.
  *
  * Returns: (transfer none) (nullable): the head element of @queue or
  * %NULL when the queue is empty.
  */
 gpointer
 gst_atomic_queue_peek (GstAtomicQueue * queue)
 {
   GstAQueueMem *head_mem;
   gint head, tail, size;

   g_return_val_if_fail (queue != NULL, NULL);

   while (TRUE) {
     GstAQueueMem *next;

     head_mem = g_atomic_pointer_get (&queue->head_mem);

     head = g_atomic_int_get (&head_mem->head);
     tail = g_atomic_int_get (&head_mem->tail_read);
     size = head_mem->size;

     /* when we are not empty, we can continue */
     if (G_LIKELY (head != tail))
       break;

     /* else array empty, try to take next */
     next = g_atomic_pointer_get (&head_mem->next);
     if (next == NULL)
       return NULL;

     /* now we try to move the next array as the head memory. If we fail to do that,
      * some other reader managed to do it first and we retry */
     if (!g_atomic_pointer_compare_and_exchange (&queue->head_mem, head_mem,
             next))
       continue;

     /* when we managed to swing the head pointer the old head is now
      * useless and we add it to the freelist. We can't free the memory yet
      * because we first need to make sure no reader is accessing it anymore. */
     add_to_free_list (queue, head_mem);
   }

   return head_mem->array[head & size];
 }

 /**
  * gst_atomic_queue_pop:
  * @queue: a #GstAtomicQueue
  *
  * Get the head element of the queue.
  *
  * Returns: (transfer full): the head element of @queue or %NULL when
  * the queue is empty.
  */
 gpointer
 gst_atomic_queue_pop (GstAtomicQueue * queue)
 {
   gpointer ret;
   GstAQueueMem *head_mem;
   gint head, tail, size;

   g_return_val_if_fail (queue != NULL, NULL);

 #ifdef LOW_MEM
   g_atomic_int_inc (&queue->num_readers);
 #endif

   do {
     while (TRUE) {
       GstAQueueMem *next;

       head_mem = g_atomic_pointer_get (&queue->head_mem);

       head = g_atomic_int_get (&head_mem->head);
       tail = g_atomic_int_get (&head_mem->tail_read);
       size = head_mem->size;

       /* when we are not empty, we can continue */
       if G_LIKELY
         (head != tail)
             break;

       /* else array empty, try to take next */
       next = g_atomic_pointer_get (&head_mem->next);
       if (next == NULL)
         return NULL;

       /* now we try to move the next array as the head memory. If we fail to do that,
        * some other reader managed to do it first and we retry */
       if G_UNLIKELY
         (!g_atomic_pointer_compare_and_exchange (&queue->head_mem, head_mem,
                 next))
             continue;

       /* when we managed to swing the head pointer the old head is now
        * useless and we add it to the freelist. We can't free the memory yet
        * because we first need to make sure no reader is accessing it anymore. */
       add_to_free_list (queue, head_mem);
     }

     ret = head_mem->array[head & size];
   } while G_UNLIKELY
   (!g_atomic_int_compare_and_exchange (&head_mem->head, head, head + 1));

 #ifdef LOW_MEM
   /* decrement number of readers, when we reach 0 readers we can be sure that
    * none is accessing the memory in the free list and we can try to clean up */
   if (g_atomic_int_dec_and_test (&queue->num_readers))
     clear_free_list (queue);
 #endif

   return ret;
 }

 /**
  * gst_atomic_queue_push:
  * @queue: a #GstAtomicQueue
  * @data: the data
  *
  * Append @data to the tail of the queue.
  */
 void
 gst_atomic_queue_push (GstAtomicQueue * queue, gpointer data)
 {
   GstAQueueMem *tail_mem;
   gint head, tail, size;

   g_return_if_fail (queue != NULL);

   do {
     while (TRUE) {
       GstAQueueMem *mem;

       tail_mem = g_atomic_pointer_get (&queue->tail_mem);
       head = g_atomic_int_get (&tail_mem->head);
       tail = g_atomic_int_get (&tail_mem->tail_write);
       size = tail_mem->size;

       /* we're not full, continue */
       if G_LIKELY
         (tail - head <= size)
             break;

       /* else we need to grow the array, we store a mask so we have to add 1 */
       mem = new_queue_mem ((size << 1) + 1, tail);

       /* try to make our new array visible to other writers */
       if G_UNLIKELY
         (!g_atomic_pointer_compare_and_exchange (&queue->tail_mem, tail_mem,
                 mem)) {
         /* we tried to swap the new writer array but something changed. This is
          * because some other writer beat us to it, we free our memory and try
          * again */
         free_queue_mem (mem);
         continue;
         }
       /* make sure that readers can find our new array as well. The one who
        * manages to swap the pointer is the only one who can set the next
        * pointer to the new array */
       g_atomic_pointer_set (&tail_mem->next, mem);
     }
   } while G_UNLIKELY
   (!g_atomic_int_compare_and_exchange (&tail_mem->tail_write, tail, tail + 1));

   tail_mem->array[tail & size] = data;

   /* now wait until all writers have completed their write before we move the
    * tail_read to this new item. It is possible that other writers are still
    * updating the previous array slots and we don't want to reveal their changes
    * before they are done. FIXME, it would be nice if we didn't have to busy
    * wait here. */
   while G_UNLIKELY
     (!g_atomic_int_compare_and_exchange (&tail_mem->tail_read, tail, tail + 1));
 }

 /**
  * gst_atomic_queue_length:
  * @queue: a #GstAtomicQueue
  *
  * Get the amount of items in the queue.
  *
  * Returns: the number of elements in the queue.
  */
 guint
 gst_atomic_queue_length (GstAtomicQueue * queue)
 {
   GstAQueueMem *head_mem, *tail_mem;
   gint head, tail;

   g_return_val_if_fail (queue != NULL, 0);

 #ifdef LOW_MEM
   g_atomic_int_inc (&queue->num_readers);
 #endif

   head_mem = g_atomic_pointer_get (&queue->head_mem);
   head = g_atomic_int_get (&head_mem->head);

   tail_mem = g_atomic_pointer_get (&queue->tail_mem);
   tail = g_atomic_int_get (&tail_mem->tail_read);

 #ifdef LOW_MEM
   if (g_atomic_int_dec_and_test (&queue->num_readers))
     clear_free_list (queue);
 #endif

   return tail - head;
 }
	/* GStreamer
	* Copyright (C) 2009 Edward Hervey <bilboed@bilboed.com>
	* 2011 Wim Taymans <wim.taymans@gmail.com>
	*
	* gstatomicqueue.c:
	*
	* 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.
	*/

	#include "gst_private.h"

	#include <string.h>

	#include <gst/gst.h>
	#include "gstatomicqueue.h"
	#include "glib-compat-private.h"

	/**
	* SECTION:gstatomicqueue
	* @title: GstAtomicQueue
	* @short_description: An atomic queue implementation
	*
	* The #GstAtomicQueue object implements a queue that can be used from multiple
	* threads without performing any blocking operations.
	*/

	G_DEFINE_BOXED_TYPE (GstAtomicQueue, gst_atomic_queue,
	(GBoxedCopyFunc) gst_atomic_queue_ref,
	(GBoxedFreeFunc) gst_atomic_queue_unref);

	/* By default the queue uses 2 * sizeof(gpointer) * clp2 (max_items) of
	* memory. clp2(x) is the next power of two >= than x.
	*
	* The queue can operate in low memory mode, in which it consumes almost
	* half the memory at the expense of extra overhead in the readers. This
	* is disabled by default because even without LOW_MEM mode, the memory
	* consumption is still lower than a plain GList.
	*/
	#undef LOW_MEM

	typedef struct _GstAQueueMem GstAQueueMem;

	struct _GstAQueueMem
	{
	gint size;
	gpointer *array;
	volatile gint head;
	volatile gint tail_write;
	volatile gint tail_read;
	GstAQueueMem *next;
	GstAQueueMem *free;
	};

	static guint
	clp2 (guint n)
	{
	guint res = 1;

	while (res < n)
	res <<= 1;

	return res;
	}

	static GstAQueueMem *
	new_queue_mem (guint size, gint pos)
	{
	GstAQueueMem *mem;

	mem = g_new (GstAQueueMem, 1);

	/* we keep the size as a mask for performance */
	mem->size = clp2 (MAX (size, 16)) - 1;
	mem->array = g_new0 (gpointer, mem->size + 1);
	mem->head = pos;
	mem->tail_write = pos;
	mem->tail_read = pos;
	mem->next = NULL;
	mem->free = NULL;

	return mem;
	}

	static void
	free_queue_mem (GstAQueueMem * mem)
	{
	g_free (mem->array);
	g_free (mem);
	}

	struct _GstAtomicQueue
	{
	volatile gint refcount;
	#ifdef LOW_MEM
	gint num_readers;
	#endif
	GstAQueueMem *head_mem;
	GstAQueueMem *tail_mem;
	GstAQueueMem *free_list;
	};

	static void
	add_to_free_list (GstAtomicQueue * queue, GstAQueueMem * mem)
	{
	do {
	mem->free = g_atomic_pointer_get (&queue->free_list);
	} while (!g_atomic_pointer_compare_and_exchange (&queue->free_list,
	mem->free, mem));
	}

	static void
	clear_free_list (GstAtomicQueue * queue)
	{
	GstAQueueMem *free_list;

	/* take the free list and replace with NULL */
	do {
	free_list = g_atomic_pointer_get (&queue->free_list);
	if (free_list == NULL)
	return;
	} while (!g_atomic_pointer_compare_and_exchange (&queue->free_list, free_list,
	NULL));

	while (free_list) {
	GstAQueueMem *next = free_list->free;

	free_queue_mem (free_list);

	free_list = next;
	}
	}

	/**
	* gst_atomic_queue_new:
	* @initial_size: initial queue size
	*
	* Create a new atomic queue instance. @initial_size will be rounded up to the
	* nearest power of 2 and used as the initial size of the queue.
	*
	* Returns: a new #GstAtomicQueue
	*/
	GstAtomicQueue *
	gst_atomic_queue_new (guint initial_size)
	{
	GstAtomicQueue *queue;

	queue = g_new (GstAtomicQueue, 1);

	queue->refcount = 1;
	#ifdef LOW_MEM
	queue->num_readers = 0;
	#endif
	queue->head_mem = queue->tail_mem = new_queue_mem (initial_size, 0);
	queue->free_list = NULL;

	return queue;
	}

	/**
	* gst_atomic_queue_ref:
	* @queue: a #GstAtomicQueue
	*
	* Increase the refcount of @queue.
	*/
	void
	gst_atomic_queue_ref (GstAtomicQueue * queue)
	{
	g_return_if_fail (queue != NULL);

	g_atomic_int_inc (&queue->refcount);
	}

	static void
	gst_atomic_queue_free (GstAtomicQueue * queue)
	{
	free_queue_mem (queue->head_mem);
	if (queue->head_mem != queue->tail_mem)
	free_queue_mem (queue->tail_mem);
	clear_free_list (queue);
	g_free (queue);
	}

	/**
	* gst_atomic_queue_unref:
	* @queue: a #GstAtomicQueue
	*
	* Unref @queue and free the memory when the refcount reaches 0.
	*/
	void
	gst_atomic_queue_unref (GstAtomicQueue * queue)
	{
	g_return_if_fail (queue != NULL);

	if (g_atomic_int_dec_and_test (&queue->refcount))
	gst_atomic_queue_free (queue);
	}

	/**
	* gst_atomic_queue_peek:
	* @queue: a #GstAtomicQueue
	*
	* Peek the head element of the queue without removing it from the queue.
	*
	* Returns: (transfer none) (nullable): the head element of @queue or
	* %NULL when the queue is empty.
	*/
	gpointer
	gst_atomic_queue_peek (GstAtomicQueue * queue)
	{
	GstAQueueMem *head_mem;
	gint head, tail, size;

	g_return_val_if_fail (queue != NULL, NULL);

	while (TRUE) {
	GstAQueueMem *next;

	head_mem = g_atomic_pointer_get (&queue->head_mem);

	head = g_atomic_int_get (&head_mem->head);
	tail = g_atomic_int_get (&head_mem->tail_read);
	size = head_mem->size;

	/* when we are not empty, we can continue */
	if (G_LIKELY (head != tail))
	break;

	/* else array empty, try to take next */
	next = g_atomic_pointer_get (&head_mem->next);
	if (next == NULL)
	return NULL;

	/* now we try to move the next array as the head memory. If we fail to do that,
	* some other reader managed to do it first and we retry */
	if (!g_atomic_pointer_compare_and_exchange (&queue->head_mem, head_mem,
	next))
	continue;

	/* when we managed to swing the head pointer the old head is now
	* useless and we add it to the freelist. We can't free the memory yet
	* because we first need to make sure no reader is accessing it anymore. */
	add_to_free_list (queue, head_mem);
	}

	return head_mem->array[head & size];
	}

	/**
	* gst_atomic_queue_pop:
	* @queue: a #GstAtomicQueue
	*
	* Get the head element of the queue.
	*
	* Returns: (transfer full): the head element of @queue or %NULL when
	* the queue is empty.
	*/
	gpointer
	gst_atomic_queue_pop (GstAtomicQueue * queue)
	{
	gpointer ret;
	GstAQueueMem *head_mem;
	gint head, tail, size;

	g_return_val_if_fail (queue != NULL, NULL);

	#ifdef LOW_MEM
	g_atomic_int_inc (&queue->num_readers);
	#endif

	do {
	while (TRUE) {
	GstAQueueMem *next;

	head_mem = g_atomic_pointer_get (&queue->head_mem);

	head = g_atomic_int_get (&head_mem->head);
	tail = g_atomic_int_get (&head_mem->tail_read);
	size = head_mem->size;

	/* when we are not empty, we can continue */
	if G_LIKELY
	(head != tail)
	break;

	/* else array empty, try to take next */
	next = g_atomic_pointer_get (&head_mem->next);
	if (next == NULL)
	return NULL;

	/* now we try to move the next array as the head memory. If we fail to do that,
	* some other reader managed to do it first and we retry */
	if G_UNLIKELY
	(!g_atomic_pointer_compare_and_exchange (&queue->head_mem, head_mem,
	next))
	continue;

	/* when we managed to swing the head pointer the old head is now
	* useless and we add it to the freelist. We can't free the memory yet
	* because we first need to make sure no reader is accessing it anymore. */
	add_to_free_list (queue, head_mem);
	}

	ret = head_mem->array[head & size];
	} while G_UNLIKELY
	(!g_atomic_int_compare_and_exchange (&head_mem->head, head, head + 1));

	#ifdef LOW_MEM
	/* decrement number of readers, when we reach 0 readers we can be sure that
	* none is accessing the memory in the free list and we can try to clean up */
	if (g_atomic_int_dec_and_test (&queue->num_readers))
	clear_free_list (queue);
	#endif

	return ret;
	}

	/**
	* gst_atomic_queue_push:
	* @queue: a #GstAtomicQueue
	* @data: the data
	*
	* Append @data to the tail of the queue.
	*/
	void
	gst_atomic_queue_push (GstAtomicQueue * queue, gpointer data)
	{
	GstAQueueMem *tail_mem;
	gint head, tail, size;

	g_return_if_fail (queue != NULL);

	do {
	while (TRUE) {
	GstAQueueMem *mem;

	tail_mem = g_atomic_pointer_get (&queue->tail_mem);
	head = g_atomic_int_get (&tail_mem->head);
	tail = g_atomic_int_get (&tail_mem->tail_write);
	size = tail_mem->size;

	/* we're not full, continue */
	if G_LIKELY
	(tail - head <= size)
	break;

	/* else we need to grow the array, we store a mask so we have to add 1 */
	mem = new_queue_mem ((size << 1) + 1, tail);

	/* try to make our new array visible to other writers */
	if G_UNLIKELY
	(!g_atomic_pointer_compare_and_exchange (&queue->tail_mem, tail_mem,
	mem)) {
	/* we tried to swap the new writer array but something changed. This is
	* because some other writer beat us to it, we free our memory and try
	* again */
	free_queue_mem (mem);
	continue;
	}
	/* make sure that readers can find our new array as well. The one who
	* manages to swap the pointer is the only one who can set the next
	* pointer to the new array */
	g_atomic_pointer_set (&tail_mem->next, mem);
	}
	} while G_UNLIKELY
	(!g_atomic_int_compare_and_exchange (&tail_mem->tail_write, tail, tail + 1));

	tail_mem->array[tail & size] = data;

	/* now wait until all writers have completed their write before we move the
	* tail_read to this new item. It is possible that other writers are still
	* updating the previous array slots and we don't want to reveal their changes
	* before they are done. FIXME, it would be nice if we didn't have to busy
	* wait here. */
	while G_UNLIKELY
	(!g_atomic_int_compare_and_exchange (&tail_mem->tail_read, tail, tail + 1));
	}

	/**
	* gst_atomic_queue_length:
	* @queue: a #GstAtomicQueue
	*
	* Get the amount of items in the queue.
	*
	* Returns: the number of elements in the queue.
	*/
	guint
	gst_atomic_queue_length (GstAtomicQueue * queue)
	{
	GstAQueueMem head_mem, tail_mem;
	gint head, tail;

	g_return_val_if_fail (queue != NULL, 0);

	#ifdef LOW_MEM
	g_atomic_int_inc (&queue->num_readers);
	#endif

	head_mem = g_atomic_pointer_get (&queue->head_mem);
	head = g_atomic_int_get (&head_mem->head);

	tail_mem = g_atomic_pointer_get (&queue->tail_mem);
	tail = g_atomic_int_get (&tail_mem->tail_read);

	#ifdef LOW_MEM
	if (g_atomic_int_dec_and_test (&queue->num_readers))
	clear_free_list (queue);
	#endif

	return tail - head;
	}