[lttng-dev] [RFC PATCH urcu] lfstack: implement pop_all and iterators
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Fri Oct 12 10:17:33 EDT 2012
Please note that this code is currently developed in a volatile branch:
git://git.dorsal.polymtl.ca/~compudj/userspace-rcu
branch: urcu/lfstack
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
---
diff --git a/lfstack.c b/lfstack.c
index 74ffd4f..7e2011d 100644
--- a/lfstack.c
+++ b/lfstack.c
@@ -45,7 +45,12 @@ int cds_lfs_push(struct cds_lfs_stack *s, struct cds_lfs_node *node)
return _cds_lfs_push(s, node);
}
-struct cds_lfs_node *cds_lfs_pop(struct cds_lfs_stack *s)
+struct cds_lfs_node *__cds_lfs_pop(struct cds_lfs_stack *s)
{
- return _cds_lfs_pop(s);
+ return ___cds_lfs_pop(s);
+}
+
+struct cds_lfs_head *__cds_lfs_pop_all(struct cds_lfs_stack *s)
+{
+ return ___cds_lfs_pop_all(s);
}
diff --git a/tests/test_urcu_lfs.c b/tests/test_urcu_lfs.c
index a29dc94..8350e65 100644
--- a/tests/test_urcu_lfs.c
+++ b/tests/test_urcu_lfs.c
@@ -244,7 +244,7 @@ void *thr_dequeuer(void *_count)
struct test *node;
rcu_read_lock();
- snode = cds_lfs_pop(&s);
+ snode = __cds_lfs_pop(&s);
node = caa_container_of(snode, struct test, list);
rcu_read_unlock();
if (node) {
@@ -275,7 +275,7 @@ void test_end(struct cds_lfs_stack *s, unsigned long long *nr_dequeues)
struct cds_lfs_node *snode;
do {
- snode = cds_lfs_pop(s);
+ snode = __cds_lfs_pop(s);
if (snode) {
struct test *node;
diff --git a/urcu/lfstack.h b/urcu/lfstack.h
index d068739..463b0d9 100644
--- a/urcu/lfstack.h
+++ b/urcu/lfstack.h
@@ -27,14 +27,40 @@
extern "C" {
#endif
+/*
+ * struct cds_lfs_node is returned by cds_lfs_pop, and also used as
+ * iterator on stack. It is not safe to dereference the node next
+ * pointer when returned by cds_lfs_pop.
+ */
struct cds_lfs_node {
struct cds_lfs_node *next;
};
+/*
+ * struct cds_lfs_head is returned by __cds_lfs_pop_all, and can be used
+ * to begin iteration on the stack.
+ */
+struct cds_lfs_head {
+ struct cds_lfs_node node;
+};
+
struct cds_lfs_stack {
- struct cds_lfs_node *head;
+ struct cds_lfs_head *head;
};
+/*
+ * 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 -
+ */
+
#ifdef _LGPL_SOURCE
#include <urcu/static/lfstack.h>
@@ -42,7 +68,8 @@ struct cds_lfs_stack {
#define cds_lfs_node_init _cds_lfs_node_init
#define cds_lfs_init _cds_lfs_init
#define cds_lfs_push _cds_lfs_push
-#define cds_lfs_pop _cds_lfs_pop
+#define __cds_lfs_pop ___cds_lfs_pop
+#define __cds_lfs_pop_all ___cds_lfs_pop_all
#else /* !_LGPL_SOURCE */
@@ -61,25 +88,74 @@ extern int cds_lfs_push(struct cds_lfs_stack *s,
struct cds_lfs_node *node);
/*
- * 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).
+ */
+extern struct cds_lfs_node *__cds_lfs_pop(struct cds_lfs_stack *s);
+
+/*
+ * __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).
*/
-extern struct cds_lfs_node *cds_lfs_pop(struct cds_lfs_stack *s);
+extern struct cds_lfs_head *__cds_lfs_pop_all(struct cds_lfs_stack *s);
#endif /* !_LGPL_SOURCE */
+/*
+ * cds_lfs_for_each: Iterate over all nodes returned by
+ * __cds_lfs_pop_all.
+ * @__head: node returned by __cds_lfs_pop_all (struct cds_lfs_node pointer).
+ * @__node: node to use as iterator (struct cds_lfs_node pointer).
+ *
+ * Content written into each node before push is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ */
+#define cds_lfs_for_each(__head, __node) \
+ for (__node = &__head->node; \
+ __node != NULL; \
+ __node = __node->next)
+
+/*
+ * cds_lfs_for_each_safe: Iterate over all nodes returned by
+ * __cds_lfs_pop_all, safe against node deletion.
+ * @__head: node returned by __cds_lfs_pop_all (struct cds_lfs_node pointer).
+ * @__node: node to use as iterator (struct cds_lfs_node pointer).
+ * @__n: struct cds_lfs_node pointer holding the next pointer (used
+ * internally).
+ *
+ * Content written into each node before push is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ */
+#define cds_lfs_for_each_safe(__head, __node, __n) \
+ for (__node = &__head->node, __n = (__node ? __node->next : NULL); \
+ __node != NULL; \
+ __node = __n, __n = (__node ? __node->next : NULL))
+
#ifdef __cplusplus
}
#endif
diff --git a/urcu/static/lfstack.h b/urcu/static/lfstack.h
index 7acbf54..479c8c3 100644
--- a/urcu/static/lfstack.h
+++ b/urcu/static/lfstack.h
@@ -33,6 +33,19 @@
extern "C" {
#endif
+/*
+ * 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 -
+ */
+
static inline
void _cds_lfs_node_init(struct cds_lfs_node *node)
{
@@ -77,21 +90,23 @@ static inline
int _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;
}
@@ -99,30 +114,31 @@ int _cds_lfs_push(struct cds_lfs_stack *s,
}
/*
- * 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;
head = _CMM_LOAD_SHARED(s->head);
if (head) {
struct cds_lfs_node *next;
+ struct cds_lfs_head *next_head;
/*
* Read head before head->next. Matches the
@@ -130,9 +146,12 @@ struct cds_lfs_node *_cds_lfs_pop(struct cds_lfs_stack *s)
* 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;
+ 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;
} else {
/* Concurrent modification. Retry. */
continue;
@@ -144,6 +163,39 @@ struct cds_lfs_node *_cds_lfs_pop(struct cds_lfs_stack *s)
}
}
+/*
+ * __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);
+}
+
#ifdef __cplusplus
}
#endif
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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