uint32_t *free_entries)
{
const uint32_t capacity = r->capacity;
+ uint32_t cons_tail;
unsigned int max = n;
int success;
+ *old_head = __atomic_load_n(&r->prod.head, __ATOMIC_RELAXED);
do {
/* Reset n to the initial burst count */
n = max;
- *old_head = __atomic_load_n(&r->prod.head,
+ /* Ensure the head is read before tail */
+ __atomic_thread_fence(__ATOMIC_ACQUIRE);
+
+ /* load-acquire synchronize with store-release of ht->tail
+ * in update_tail.
+ */
+ cons_tail = __atomic_load_n(&r->cons.tail,
__ATOMIC_ACQUIRE);
- const uint32_t cons_tail = r->cons.tail;
- /*
- * The subtraction is done between two unsigned 32bits value
+
+ /* The subtraction is done between two unsigned 32bits value
* (the result is always modulo 32 bits even if we have
* *old_head > cons_tail). So 'free_entries' is always between 0
* and capacity (which is < size).
if (is_sp)
r->prod.head = *new_head, success = 1;
else
+ /* on failure, *old_head is updated */
success = __atomic_compare_exchange_n(&r->prod.head,
old_head, *new_head,
- 0, __ATOMIC_ACQUIRE,
+ 0, __ATOMIC_RELAXED,
__ATOMIC_RELAXED);
} while (unlikely(success == 0));
return n;
uint32_t *entries)
{
unsigned int max = n;
+ uint32_t prod_tail;
int success;
/* move cons.head atomically */
+ *old_head = __atomic_load_n(&r->cons.head, __ATOMIC_RELAXED);
do {
/* Restore n as it may change every loop */
n = max;
- *old_head = __atomic_load_n(&r->cons.head,
+
+ /* Ensure the head is read before tail */
+ __atomic_thread_fence(__ATOMIC_ACQUIRE);
+
+ /* this load-acquire synchronize with store-release of ht->tail
+ * in update_tail.
+ */
+ prod_tail = __atomic_load_n(&r->prod.tail,
__ATOMIC_ACQUIRE);
- const uint32_t prod_tail = r->prod.tail;
+
/* The subtraction is done between two unsigned 32bits value
* (the result is always modulo 32 bits even if we have
* cons_head > prod_tail). So 'entries' is always between 0
if (is_sc)
r->cons.head = *new_head, success = 1;
else
+ /* on failure, *old_head will be updated */
success = __atomic_compare_exchange_n(&r->cons.head,
old_head, *new_head,
- 0, __ATOMIC_ACQUIRE,
+ 0, __ATOMIC_RELAXED,
__ATOMIC_RELAXED);
} while (unlikely(success == 0));
return n;