* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
+#include <stdbool.h>
+#include <pthread.h>
+#include <assert.h>
#include <urcu/uatomic.h>
#include <urcu-pointer.h>
extern "C" {
#endif
+/*
+ * Lock-free stack.
+ *
+ * Stack implementing push, pop, pop_all operations, as well as iterator
+ * on the stack head returned by pop_all.
+ *
+ * Synchronization table:
+ *
+ * External synchronization techniques described in the API below is
+ * required between pairs marked with "X". No external synchronization
+ * required between pairs marked with "-".
+ *
+ * cds_lfs_push __cds_lfs_pop __cds_lfs_pop_all
+ * cds_lfs_push - - -
+ * __cds_lfs_pop - X X
+ * __cds_lfs_pop_all - X -
+ *
+ * cds_lfs_pop_blocking and cds_lfs_pop_all_blocking use an internal
+ * mutex to provide synchronization.
+ */
+
+/*
+ * cds_lfs_node_init: initialize lock-free stack node.
+ */
static inline
void _cds_lfs_node_init(struct cds_lfs_node *node)
{
}
+/*
+ * cds_lfs_init: initialize lock-free stack.
+ */
static inline
void _cds_lfs_init(struct cds_lfs_stack *s)
{
+ int ret;
+
s->head = NULL;
+ ret = pthread_mutex_init(&s->lock, NULL);
+ assert(!ret);
+}
+
+static inline
+bool ___cds_lfs_empty_head(struct cds_lfs_head *head)
+{
+ return head == NULL;
+}
+
+/*
+ * cds_lfs_empty: return whether lock-free stack is empty.
+ *
+ * No memory barrier is issued. No mutual exclusion is required.
+ */
+static inline
+bool _cds_lfs_empty(struct cds_lfs_stack *s)
+{
+ return ___cds_lfs_empty_head(CMM_LOAD_SHARED(s->head));
}
/*
* Returns non-zero otherwise.
*/
static inline
-int _cds_lfs_push(struct cds_lfs_stack *s,
+bool _cds_lfs_push(struct cds_lfs_stack *s,
struct cds_lfs_node *node)
{
- struct cds_lfs_node *head = NULL;
+ struct cds_lfs_head *head = NULL;
+ struct cds_lfs_head *new_head =
+ caa_container_of(node, struct cds_lfs_head, node);
for (;;) {
- struct cds_lfs_node *old_head = head;
+ struct cds_lfs_head *old_head = head;
/*
* node->next is still private at this point, no need to
* perform a _CMM_STORE_SHARED().
*/
- node->next = head;
+ node->next = &head->node;
/*
* uatomic_cmpxchg() implicit memory barrier orders earlier
* stores to node before publication.
*/
- head = uatomic_cmpxchg(&s->head, old_head, node);
+ head = uatomic_cmpxchg(&s->head, old_head, new_head);
if (old_head == head)
break;
}
- return (int) !!((unsigned long) head);
+ return ___cds_lfs_empty_head(head);
}
/*
- * cds_lfs_pop: pop a node from the stack.
+ * __cds_lfs_pop: pop a node from the stack.
*
* Returns NULL if stack is empty.
*
- * cds_lfs_pop needs to be synchronized using one of the following
+ * __cds_lfs_pop needs to be synchronized using one of the following
* techniques:
*
- * 1) Calling cds_lfs_pop under rcu read lock critical section. The
+ * 1) Calling __cds_lfs_pop under rcu read lock critical section. The
* caller must wait for a grace period to pass before freeing the
* returned node or modifying the cds_lfs_node structure.
- * 2) Using mutual exclusion (e.g. mutexes) to protect cds_lfs_pop
- * callers.
- * 3) Ensuring that only ONE thread can call cds_lfs_pop().
- * (multi-provider/single-consumer scheme).
+ * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop
+ * and __cds_lfs_pop_all callers.
+ * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and
+ * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme).
*/
static inline
-struct cds_lfs_node *_cds_lfs_pop(struct cds_lfs_stack *s)
+struct cds_lfs_node *___cds_lfs_pop(struct cds_lfs_stack *s)
{
for (;;) {
- struct cds_lfs_node *head;
+ struct cds_lfs_head *head, *next_head;
+ struct cds_lfs_node *next;
head = _CMM_LOAD_SHARED(s->head);
- if (head) {
- struct cds_lfs_node *next;
-
- /*
- * Read head before head->next. Matches the
- * implicit memory barrier before
- * uatomic_cmpxchg() in cds_lfs_push.
- */
- cmm_smp_read_barrier_depends();
- next = _CMM_LOAD_SHARED(head->next);
- if (uatomic_cmpxchg(&s->head, head, next) == head) {
- return head;
- } else {
- /* Concurrent modification. Retry. */
- continue;
- }
- } else {
- /* Empty stack */
- return NULL;
- }
+ if (___cds_lfs_empty_head(head))
+ return NULL; /* Empty stack */
+
+ /*
+ * Read head before head->next. Matches the implicit
+ * memory barrier before uatomic_cmpxchg() in
+ * cds_lfs_push.
+ */
+ cmm_smp_read_barrier_depends();
+ next = _CMM_LOAD_SHARED(head->node.next);
+ next_head = caa_container_of(next,
+ struct cds_lfs_head, node);
+ if (uatomic_cmpxchg(&s->head, head, next_head) == head)
+ return &head->node;
+ /* busy-loop if head changed under us */
}
}
+/*
+ * __cds_lfs_pop_all: pop all nodes from a stack.
+ *
+ * __cds_lfs_pop_all does not require any synchronization with other
+ * push, nor with other __cds_lfs_pop_all, but requires synchronization
+ * matching the technique used to synchronize __cds_lfs_pop:
+ *
+ * 1) If __cds_lfs_pop is called under rcu read lock critical section,
+ * both __cds_lfs_pop and cds_lfs_pop_all callers must wait for a
+ * grace period to pass before freeing the returned node or modifying
+ * the cds_lfs_node structure. However, no RCU read-side critical
+ * section is needed around __cds_lfs_pop_all.
+ * 2) Using mutual exclusion (e.g. mutexes) to protect __cds_lfs_pop and
+ * __cds_lfs_pop_all callers.
+ * 3) Ensuring that only ONE thread can call __cds_lfs_pop() and
+ * __cds_lfs_pop_all(). (multi-provider/single-consumer scheme).
+ */
+static inline
+struct cds_lfs_head *___cds_lfs_pop_all(struct cds_lfs_stack *s)
+{
+ /*
+ * Implicit memory barrier after uatomic_xchg() matches implicit
+ * memory barrier before uatomic_cmpxchg() in cds_lfs_push. It
+ * ensures that all nodes of the returned list are consistent.
+ * There is no need to issue memory barriers when iterating on
+ * the returned list, because the full memory barrier issued
+ * prior to each uatomic_cmpxchg, which each write to head, are
+ * taking care to order writes to each node prior to the full
+ * memory barrier after this uatomic_xchg().
+ */
+ return uatomic_xchg(&s->head, NULL);
+}
+
+/*
+ * cds_lfs_pop_lock: lock stack pop-protection mutex.
+ */
+static inline void _cds_lfs_pop_lock(struct cds_lfs_stack *s)
+{
+ int ret;
+
+ ret = pthread_mutex_lock(&s->lock);
+ assert(!ret);
+}
+
+/*
+ * cds_lfs_pop_unlock: unlock stack pop-protection mutex.
+ */
+static inline void _cds_lfs_pop_unlock(struct cds_lfs_stack *s)
+{
+ int ret;
+
+ ret = pthread_mutex_unlock(&s->lock);
+ assert(!ret);
+}
+
+/*
+ * Call __cds_lfs_pop with an internal pop mutex held.
+ */
+static inline
+struct cds_lfs_node *
+_cds_lfs_pop_blocking(struct cds_lfs_stack *s)
+{
+ struct cds_lfs_node *retnode;
+
+ _cds_lfs_pop_lock(s);
+ retnode = ___cds_lfs_pop(s);
+ _cds_lfs_pop_unlock(s);
+ return retnode;
+}
+
+/*
+ * Call __cds_lfs_pop_all with an internal pop mutex held.
+ */
+static inline
+struct cds_lfs_head *
+_cds_lfs_pop_all_blocking(struct cds_lfs_stack *s)
+{
+ struct cds_lfs_head *rethead;
+
+ _cds_lfs_pop_lock(s);
+ rethead = ___cds_lfs_pop_all(s);
+ _cds_lfs_pop_unlock(s);
+ return rethead;
+}
+
#ifdef __cplusplus
}
#endif
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