gint size;
gpointer *array;
volatile gint head;
- volatile gint tail;
+ volatile gint tail_write;
volatile gint tail_read;
GstAQueueMem *next;
GstAQueueMem *free;
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;
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 (&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
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 (&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;
- /* and now the readers can read */
- g_atomic_int_inc (&tail_mem->tail_read);
+ /* 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));
}
/**