*
* 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., 59 Temple Place - Suite 330,
- * Boston, MA 02111-1307, USA.
+ * 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.
gint size;
gpointer *array;
volatile gint head;
- volatile gint tail;
+ volatile gint tail_write;
+ volatile gint tail_read;
GstAQueueMem *next;
GstAQueueMem *free;
};
mem = g_new (GstAQueueMem, 1);
/* we keep the size as a mask for performance */
- mem->size = clp2 (size) - 1;
- mem->array = g_new0 (gpointer, mem->size);
+ mem->size = clp2 (MAX (size, 16)) - 1;
+ mem->array = g_new0 (gpointer, mem->size + 1);
mem->head = pos;
- mem->tail = pos;
+ mem->tail_write = pos;
+ mem->tail_read = pos;
mem->next = NULL;
mem->free = NULL;
struct _GstAtomicQueue
{
+ volatile gint refcount;
#ifdef LOW_MEM
gint num_readers;
#endif
{
do {
mem->free = g_atomic_pointer_get (&queue->free_list);
- } while (!g_atomic_pointer_compare_and_exchange ((gpointer *) &
- queue->free_list, mem->free, mem));
+ } while (!g_atomic_pointer_compare_and_exchange (&queue->free_list,
+ mem->free, mem));
}
static void
free_list = g_atomic_pointer_get (&queue->free_list);
if (free_list == NULL)
return;
- } while (!g_atomic_pointer_compare_and_exchange ((gpointer *) &
- queue->free_list, free_list, NULL));
+ } while (!g_atomic_pointer_compare_and_exchange (&queue->free_list, free_list,
+ NULL));
while (free_list) {
GstAQueueMem *next = free_list->free;
}
}
+/**
+ * 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)
{
queue = g_new (GstAtomicQueue, 1);
+ queue->refcount = 1;
#ifdef LOW_MEM
queue->num_readers = 0;
#endif
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);
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);
+ tail = g_atomic_int_get (&head_mem->tail_read);
size = head_mem->size;
/* when we are not empty, we can continue */
/* 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 ((gpointer *) &
- queue->head_mem, head_mem, next))
+ 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
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)
{
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
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);
+ 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;
+ if G_LIKELY
+ (head != tail)
+ break;
/* else array empty, try to take next */
next = g_atomic_pointer_get (&head_mem->next);
/* 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 ((gpointer *) &
- queue->head_mem, head_mem, next))
- continue;
+ 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
}
ret = head_mem->array[head & size];
- } while (!g_atomic_int_compare_and_exchange (&head_mem->head, head,
- head + 1));
+ } 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
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);
+ tail = g_atomic_int_get (&tail_mem->tail_write);
size = tail_mem->size;
/* we're not full, continue */
- if (tail - head < size)
- break;
+ 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_atomic_pointer_compare_and_exchange ((gpointer *) &
- queue->tail_mem, tail_mem, mem)) {
+ 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_atomic_int_compare_and_exchange (&tail_mem->tail, tail,
- tail + 1));
+ } 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 = g_atomic_int_get (&head_mem->head);
tail_mem = g_atomic_pointer_get (&queue->tail_mem);
- tail = g_atomic_int_get (&tail_mem->tail);
+ tail = g_atomic_int_get (&tail_mem->tail_read);
#ifdef LOW_MEM
if (g_atomic_int_dec_and_test (&queue->num_readers))
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