Cleanup: Re-organise source dir

[userspace-rcu.git] / include / urcu / static / rculfstack.h

diff --git a/include/urcu/static/rculfstack.h b/include/urcu/static/rculfstack.h
new file mode 100644 (file)
index 0000000..3473cce
--- /dev/null
+++ b/include/urcu/static/rculfstack.h
@@ -0,0 +1,128 @@
+#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 */