lfstack: relax constraints on node re-use

[urcu.git] / urcu / lfstack.h

diff --git a/urcu/lfstack.h b/urcu/lfstack.h
index eddff0ef519be68d97776b3195054a07c845f2af..11a63d95cd3322a00c052a79080f1f93dd99e31c 100644 (file)
--- a/urcu/lfstack.h
+++ b/urcu/lfstack.h
@@ -70,17 +70,32 @@ struct cds_lfs_head {
        struct cds_lfs_node node;
 };
 
+struct __cds_lfs_stack {
+       struct cds_lfs_head *head;
+};
+
 struct cds_lfs_stack {
        struct cds_lfs_head *head;
        pthread_mutex_t lock;
 };
 
+/*
+ * The transparent union allows calling functions that work on both
+ * struct cds_lfs_stack and struct __cds_lfs_stack on any of those two
+ * types.
+ */
+typedef union {
+       struct __cds_lfs_stack *_s;
+       struct cds_lfs_stack *s;
+} __attribute__((__transparent_union__)) cds_lfs_stack_ptr_t;
+
 #ifdef _LGPL_SOURCE
 
 #include <urcu/static/lfstack.h>
 
 #define cds_lfs_node_init              _cds_lfs_node_init
 #define cds_lfs_init                   _cds_lfs_init
+#define __cds_lfs_init                 ___cds_lfs_init
 #define cds_lfs_empty                  _cds_lfs_empty
 #define cds_lfs_push                   _cds_lfs_push
 
@@ -108,12 +123,17 @@ extern void cds_lfs_node_init(struct cds_lfs_node *node);
  */
 extern void cds_lfs_init(struct cds_lfs_stack *s);
 
+/*
+ * __cds_lfs_init: initialize lock-free stack.
+ */
+extern void __cds_lfs_init(struct __cds_lfs_stack *s);
+
 /*
  * cds_lfs_empty: return whether lock-free stack is empty.
  *
  * No memory barrier is issued. No mutual exclusion is required.
  */
-extern bool cds_lfs_empty(struct cds_lfs_stack *s);
+extern bool cds_lfs_empty(cds_lfs_stack_ptr_t s);
 
 /*
  * cds_lfs_push: push a node into the stack.
@@ -123,7 +143,7 @@ extern bool cds_lfs_empty(struct cds_lfs_stack *s);
  * Returns 0 if the stack was empty prior to adding the node.
  * Returns non-zero otherwise.
  */
-extern bool cds_lfs_push(struct cds_lfs_stack *s,
+extern bool cds_lfs_push(cds_lfs_stack_ptr_t s,
                        struct cds_lfs_node *node);
 
 /*
@@ -158,15 +178,18 @@ extern void cds_lfs_pop_unlock(struct cds_lfs_stack *s);
  * __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
- *    caller must wait for a grace period to pass before freeing the
- *    returned node or modifying the cds_lfs_node structure.
+ * 1) Calling __cds_lfs_pop 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 pushing
+ *    the node back into the stack. It is valid to overwrite the content
+ *    of cds_lfs_node immediately after __cds_lfs_pop and
+ *    __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_node *__cds_lfs_pop(cds_lfs_stack_ptr_t s);
 
 /*
  * __cds_lfs_pop_all: pop all nodes from a stack.
@@ -176,16 +199,18 @@ extern struct cds_lfs_node *__cds_lfs_pop(struct cds_lfs_stack *s);
  * 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.
+ *    both __cds_lfs_pop and __cds_lfs_pop_all callers must wait for a
+ *    grace period to pass before freeing the returned node or pushing
+ *    the node back into the stack. It is valid to overwrite the content
+ *    of cds_lfs_node immediately after __cds_lfs_pop and
+ *    __cds_lfs_pop_all. 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_head *__cds_lfs_pop_all(struct cds_lfs_stack *s);
+extern struct cds_lfs_head *__cds_lfs_pop_all(cds_lfs_stack_ptr_t s);
 
 #endif /* !_LGPL_SOURCE */