X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=blobdiff_plain;f=include%2Furcu%2Fstatic%2Frculfstack.h;fp=include%2Furcu%2Fstatic%2Frculfstack.h;h=3473ccef82299b0b41559734e75377b2ac0f1941;hp=0000000000000000000000000000000000000000;hb=6893800a4d1cc14dff0395ddcd660a5138db183d;hpb=a59f39055b5ecb77b68cf78b9839aa9e8e4ec332

diff --git a/include/urcu/static/rculfstack.h b/include/urcu/static/rculfstack.h
new file mode 100644
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+++ b/include/urcu/static/rculfstack.h
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+#ifndef _URCU_RCULFSTACK_STATIC_H
+#define _URCU_RCULFSTACK_STATIC_H
+
+/*
+ * rculfstack-static.h
+ *
+ * Userspace RCU library - Lock-Free RCU Stack
+ *
+ * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See rculfstack.h for linking
+ * dynamically with the userspace rcu library.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <urcu/uatomic.h>
+#include <urcu-pointer.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static inline
+void _cds_lfs_node_init_rcu(struct cds_lfs_node_rcu *node)
+{
+}
+
+static inline
+void _cds_lfs_init_rcu(struct cds_lfs_stack_rcu *s)
+{
+	s->head = NULL;
+}
+
+/*
+ * Lock-free stack push is not subject to ABA problem, so no need to
+ * take the RCU read-side lock. Even if "head" changes between two
+ * uatomic_cmpxchg() invocations here (being popped, and then pushed
+ * again by one or more concurrent threads), the second
+ * uatomic_cmpxchg() invocation only cares about pushing a new entry at
+ * the head of the stack, ensuring consistency by making sure the new
+ * node->next is the same pointer value as the value replaced as head.
+ * It does not care about the content of the actual next node, so it can
+ * very well be reallocated between the two uatomic_cmpxchg().
+ *
+ * We take the approach of expecting the stack to be usually empty, so
+ * we first try an initial uatomic_cmpxchg() on a NULL old_head, and
+ * retry if the old head was non-NULL (the value read by the first
+ * uatomic_cmpxchg() is used as old head for the following loop). The
+ * upside of this scheme is to minimize the amount of cacheline traffic,
+ * always performing an exclusive cacheline access, rather than doing
+ * non-exclusive followed by exclusive cacheline access (which would be
+ * required if we first read the old head value). This design decision
+ * might be revisited after more throrough benchmarking on various
+ * platforms.
+ *
+ * Returns 0 if the stack was empty prior to adding the node.
+ * Returns non-zero otherwise.
+ */
+static inline
+int _cds_lfs_push_rcu(struct cds_lfs_stack_rcu *s,
+			  struct cds_lfs_node_rcu *node)
+{
+	struct cds_lfs_node_rcu *head = NULL;
+
+	for (;;) {
+		struct cds_lfs_node_rcu *old_head = head;
+
+		node->next = head;
+		/*
+		 * uatomic_cmpxchg() implicit memory barrier orders earlier
+		 * stores to node before publication.
+		 */
+		head = uatomic_cmpxchg(&s->head, old_head, node);
+		if (old_head == head)
+			break;
+	}
+	return (int) !!((unsigned long) head);
+}
+
+/*
+ * Should be called under rcu read-side lock.
+ *
+ * The caller must wait for a grace period to pass before freeing the returned
+ * node or modifying the cds_lfs_node_rcu structure.
+ * Returns NULL if stack is empty.
+ */
+static inline
+struct cds_lfs_node_rcu *
+_cds_lfs_pop_rcu(struct cds_lfs_stack_rcu *s)
+{
+	for (;;) {
+		struct cds_lfs_node_rcu *head;
+
+		head = rcu_dereference(s->head);
+		if (head) {
+			struct cds_lfs_node_rcu *next = rcu_dereference(head->next);
+
+			if (uatomic_cmpxchg(&s->head, head, next) == head) {
+				return head;
+			} else {
+				/* Concurrent modification. Retry. */
+				continue;
+			}
+		} else {
+			/* Empty stack */
+			return NULL;
+		}
+	}
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _URCU_RCULFSTACK_STATIC_H */