#define _URCU_WFSTACK_H
/*
- * rcuwfstack.h
+ * urcu/wfstack.h
*
- * Userspace RCU library - Stack with Wait-Free push, Blocking pop.
+ * Userspace RCU library - Stack with wait-free push, blocking traversal.
*
- * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
#include <pthread.h>
#include <assert.h>
+#include <stdbool.h>
#include <urcu/compiler.h>
#ifdef __cplusplus
extern "C" {
#endif
-#if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
-#error "Dynamic loader LGPL wrappers not implemented yet"
-#endif
+/*
+ * Stack with wait-free push, blocking traversal.
+ *
+ * Stack implementing push, pop, pop_all operations, as well as iterator
+ * on the stack head returned by pop_all.
+ *
+ * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all, cds_wfs_empty,
+ * cds_wfs_first.
+ * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next,
+ * iteration on 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_wfs_push __cds_wfs_pop __cds_wfs_pop_all
+ * cds_wfs_push - - -
+ * __cds_wfs_pop - X X
+ * __cds_wfs_pop_all - X -
+ *
+ * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
+ * synchronization.
+ */
-#define WF_STACK_END ((void *)0x1UL)
-#define WFS_ADAPT_ATTEMPTS 10 /* Retry if being set */
-#define WFS_WAIT 10 /* Wait 10 ms if being set */
+#define CDS_WFS_WOULDBLOCK ((void *) -1UL)
-struct wfs_node {
- struct wfs_node *next;
+enum cds_wfs_state {
+ CDS_WFS_STATE_LAST = (1U << 0),
};
-struct wfs_stack {
- struct wfs_node *head;
+/*
+ * struct cds_wfs_node is returned by __cds_wfs_pop, and also used as
+ * iterator on stack. It is not safe to dereference the node next
+ * pointer when returned by __cds_wfs_pop_blocking.
+ */
+struct cds_wfs_node {
+ struct cds_wfs_node *next;
+};
+
+/*
+ * struct cds_wfs_head is returned by __cds_wfs_pop_all, and can be used
+ * to begin iteration on the stack. "node" needs to be the first field of
+ * cds_wfs_head, so the end-of-stack pointer value can be used for both
+ * types.
+ */
+struct cds_wfs_head {
+ struct cds_wfs_node node;
+};
+
+struct __cds_wfs_stack {
+ struct cds_wfs_head *head;
+};
+
+struct cds_wfs_stack {
+ struct cds_wfs_head *head;
pthread_mutex_t lock;
};
-void wfs_node_init(struct wfs_node *node)
-{
- node->next = NULL;
-}
+/*
+ * The transparent union allows calling functions that work on both
+ * struct cds_wfs_stack and struct __cds_wfs_stack on any of those two
+ * types.
+ */
+typedef union {
+ struct __cds_wfs_stack *_s;
+ struct cds_wfs_stack *s;
+} __attribute__((__transparent_union__)) cds_wfs_stack_ptr_t;
-void wfs_init(struct wfs_stack *s)
-{
- int ret;
+#ifdef _LGPL_SOURCE
- s->head = WF_STACK_END;
- ret = pthread_mutex_init(&s->lock, NULL);
- assert(!ret);
-}
+#include <urcu/static/wfstack.h>
-void wfs_push(struct wfs_stack *s, struct wfs_node *node)
-{
- struct wfs_node *old_head;
-
- assert(node->next == NULL);
- /*
- * uatomic_xchg() implicit memory barrier orders earlier stores to node
- * (setting it to NULL) before publication.
- */
- old_head = uatomic_xchg(&s->head, node);
- /*
- * At this point, dequeuers see a NULL node->next, they should busy-wait
- * until node->next is set to old_head.
- */
- STORE_SHARED(node->next, old_head);
-}
+#define cds_wfs_node_init _cds_wfs_node_init
+#define cds_wfs_init _cds_wfs_init
+#define cds_wfs_destroy _cds_wfs_destroy
+#define __cds_wfs_init ___cds_wfs_init
+#define cds_wfs_empty _cds_wfs_empty
+#define cds_wfs_push _cds_wfs_push
+
+/* Locking performed internally */
+#define cds_wfs_pop_blocking _cds_wfs_pop_blocking
+#define cds_wfs_pop_with_state_blocking _cds_wfs_pop_with_state_blocking
+#define cds_wfs_pop_all_blocking _cds_wfs_pop_all_blocking
+
+/*
+ * For iteration on cds_wfs_head returned by __cds_wfs_pop_all or
+ * cds_wfs_pop_all_blocking.
+ */
+#define cds_wfs_first _cds_wfs_first
+#define cds_wfs_next_blocking _cds_wfs_next_blocking
+#define cds_wfs_next_nonblocking _cds_wfs_next_nonblocking
+
+/* Pop locking with internal mutex */
+#define cds_wfs_pop_lock _cds_wfs_pop_lock
+#define cds_wfs_pop_unlock _cds_wfs_pop_unlock
+
+/* Synchronization ensured by the caller. See synchronization table. */
+#define __cds_wfs_pop_blocking ___cds_wfs_pop_blocking
+#define __cds_wfs_pop_with_state_blocking \
+ ___cds_wfs_pop_with_state_blocking
+#define __cds_wfs_pop_nonblocking ___cds_wfs_pop_nonblocking
+#define __cds_wfs_pop_with_state_nonblocking \
+ ___cds_wfs_pop_with_state_nonblocking
+#define __cds_wfs_pop_all ___cds_wfs_pop_all
+
+#else /* !_LGPL_SOURCE */
+
+/*
+ * cds_wfs_node_init: initialize wait-free stack node.
+ */
+extern void cds_wfs_node_init(struct cds_wfs_node *node);
+
+/*
+ * cds_wfs_init: initialize wait-free stack (with lock). Pair with
+ * cds_wfs_destroy().
+ */
+extern void cds_wfs_init(struct cds_wfs_stack *s);
+
+/*
+ * cds_wfs_destroy: destroy wait-free stack (with lock). Pair with
+ * cds_wfs_init().
+ */
+extern void cds_wfs_destroy(struct cds_wfs_stack *s);
+
+/*
+ * __cds_wfs_init: initialize wait-free stack (no lock). Don't pair with
+ * any destroy function.
+ */
+extern void __cds_wfs_init(struct __cds_wfs_stack *s);
+
+/*
+ * cds_wfs_empty: return whether wait-free stack is empty.
+ *
+ * No memory barrier is issued. No mutual exclusion is required.
+ */
+extern bool cds_wfs_empty(cds_wfs_stack_ptr_t u_stack);
+
+/*
+ * cds_wfs_push: push a node into the stack.
+ *
+ * Issues a full memory barrier before push. No mutual exclusion is
+ * required.
+ *
+ * Returns 0 if the stack was empty prior to adding the node.
+ * Returns non-zero otherwise.
+ */
+extern int cds_wfs_push(cds_wfs_stack_ptr_t u_stack, struct cds_wfs_node *node);
+
+/*
+ * cds_wfs_pop_blocking: pop a node from the stack.
+ *
+ * Calls __cds_wfs_pop_blocking with an internal pop mutex held.
+ */
+extern struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s);
+
+/*
+ * cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
+ *
+ * Same as cds_wfs_pop_blocking, but stores whether the stack was
+ * empty into state (CDS_WFS_STATE_LAST).
+ */
+extern struct cds_wfs_node *
+ cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state);
+
+/*
+ * cds_wfs_pop_all_blocking: pop all nodes from a stack.
+ *
+ * Calls __cds_wfs_pop_all with an internal pop mutex held.
+ */
+extern struct cds_wfs_head *cds_wfs_pop_all_blocking(struct cds_wfs_stack *s);
/*
+ * cds_wfs_first: get first node of a popped stack.
+ *
+ * Content written into the node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ *
+ * Used by for-like iteration macros in urcu/wfstack.h:
+ * cds_wfs_for_each_blocking()
+ * cds_wfs_for_each_blocking_safe()
+ *
+ * Returns NULL if popped stack is empty, top stack node otherwise.
+ */
+extern struct cds_wfs_node *cds_wfs_first(struct cds_wfs_head *head);
+
+/*
+ * cds_wfs_next_blocking: get next node of a popped stack.
+ *
+ * Content written into the node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ *
+ * Used by for-like iteration macros in urcu/wfstack.h:
+ * cds_wfs_for_each_blocking()
+ * cds_wfs_for_each_blocking_safe()
+ *
+ * Returns NULL if reached end of popped stack, non-NULL next stack
+ * node otherwise.
+ */
+extern struct cds_wfs_node *cds_wfs_next_blocking(struct cds_wfs_node *node);
+
+/*
+ * cds_wfs_next_nonblocking: get next node of a popped stack.
+ *
+ * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
+ * needs to block.
+ */
+extern struct cds_wfs_node *cds_wfs_next_nonblocking(struct cds_wfs_node *node);
+
+/*
+ * cds_wfs_pop_lock: lock stack pop-protection mutex.
+ */
+extern void cds_wfs_pop_lock(struct cds_wfs_stack *s);
+
+/*
+ * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
+ */
+extern void cds_wfs_pop_unlock(struct cds_wfs_stack *s);
+
+/*
+ * __cds_wfs_pop_blocking: pop a node from the stack.
+ *
* Returns NULL if stack is empty.
+ *
+ * __cds_wfs_pop_blocking needs to be synchronized using one of the
+ * following techniques:
+ *
+ * 1) Calling __cds_wfs_pop_blocking 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_wfs_node structure.
+ * 2) Using mutual exclusion (e.g. mutexes) to protect
+ * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
+ * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
+ * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
*/
-struct wfs_node *
-__wfs_pop_blocking(struct wfs_stack *s)
-{
- struct wfs_node *head, *next;
- int attempt = 0;
-
-retry:
- head = LOAD_SHARED(s->head);
- if (head == WF_STACK_END)
- return NULL;
- /*
- * Adaptative busy-looping waiting for push to complete.
- */
- while ((next = LOAD_SHARED(head->next)) == NULL) {
- if (++attempt >= WFS_ADAPT_ATTEMPTS) {
- poll(NULL, 0, WFS_WAIT); /* Wait for 10ms */
- attempt = 0;
- } else
- cpu_relax();
- }
- if (uatomic_cmpxchg(&s->head, head, next) == head)
- return head;
- else
- goto retry; /* Concurrent modification. Retry. */
-}
+extern struct cds_wfs_node *__cds_wfs_pop_blocking(cds_wfs_stack_ptr_t u_stack);
-struct wfs_node *
-wfs_pop_blocking(struct wfs_stack *s)
-{
- struct wfs_node *retnode;
- int ret;
-
- ret = pthread_mutex_lock(&s->lock);
- assert(!ret);
- retnode = __wfs_pop_blocking(s);
- ret = pthread_mutex_unlock(&s->lock);
- assert(!ret);
- return retnode;
-}
+/*
+ * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
+ *
+ * Same as __cds_wfs_pop_blocking, but stores whether the stack was
+ * empty into state (CDS_WFS_STATE_LAST).
+ */
+extern struct cds_wfs_node *
+ __cds_wfs_pop_with_state_blocking(cds_wfs_stack_ptr_t u_stack,
+ int *state);
+
+/*
+ * __cds_wfs_pop_nonblocking: pop a node from the stack.
+ *
+ * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
+ * it needs to block.
+ */
+extern struct cds_wfs_node *__cds_wfs_pop_nonblocking(cds_wfs_stack_ptr_t u_stack);
+
+/*
+ * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack, with state.
+ *
+ * Same as __cds_wfs_pop_nonblocking, but stores whether the stack was
+ * empty into state (CDS_WFS_STATE_LAST).
+ */
+extern struct cds_wfs_node *
+ __cds_wfs_pop_with_state_nonblocking(cds_wfs_stack_ptr_t u_stack,
+ int *state);
+
+/*
+ * __cds_wfs_pop_all: pop all nodes from a stack.
+ *
+ * __cds_wfs_pop_all does not require any synchronization with other
+ * push, nor with other __cds_wfs_pop_all, but requires synchronization
+ * matching the technique used to synchronize __cds_wfs_pop_blocking:
+ *
+ * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical
+ * section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers
+ * must wait for a grace period to pass before freeing the returned
+ * node or modifying the cds_wfs_node structure. However, no RCU
+ * read-side critical section is needed around __cds_wfs_pop_all.
+ * 2) Using mutual exclusion (e.g. mutexes) to protect
+ * __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
+ * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
+ * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
+ */
+extern struct cds_wfs_head *__cds_wfs_pop_all(cds_wfs_stack_ptr_t u_stack);
+
+#endif /* !_LGPL_SOURCE */
#ifdef __cplusplus
}
#endif
+/*
+ * cds_wfs_for_each_blocking: Iterate over all nodes returned by
+ * __cds_wfs_pop_all().
+ * @head: head of the queue (struct cds_wfs_head pointer).
+ * @node: iterator (struct cds_wfs_node pointer).
+ *
+ * Content written into each node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ */
+#define cds_wfs_for_each_blocking(head, node) \
+ for (node = cds_wfs_first(head); \
+ node != NULL; \
+ node = cds_wfs_next_blocking(node))
+
+/*
+ * cds_wfs_for_each_blocking_safe: Iterate over all nodes returned by
+ * __cds_wfs_pop_all(). Safe against deletion.
+ * @head: head of the queue (struct cds_wfs_head pointer).
+ * @node: iterator (struct cds_wfs_node pointer).
+ * @n: struct cds_wfs_node pointer holding the next pointer (used
+ * internally).
+ *
+ * Content written into each node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ */
+#define cds_wfs_for_each_blocking_safe(head, node, n) \
+ for (node = cds_wfs_first(head), \
+ n = (node ? cds_wfs_next_blocking(node) : NULL); \
+ node != NULL; \
+ node = n, n = (node ? cds_wfs_next_blocking(node) : NULL))
+
#endif /* _URCU_WFSTACK_H */
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