1 #ifndef _URCU_RCULFSTACK_STATIC_H
2 #define _URCU_RCULFSTACK_STATIC_H
7 * Userspace RCU library - Lock-Free RCU Stack
9 * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
11 * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See rculfstack.h for linking
12 * dynamically with the userspace rcu library.
14 * This library is free software; you can redistribute it and/or
15 * modify it under the terms of the GNU Lesser General Public
16 * License as published by the Free Software Foundation; either
17 * version 2.1 of the License, or (at your option) any later version.
19 * This library is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
22 * Lesser General Public License for more details.
24 * You should have received a copy of the GNU Lesser General Public
25 * License along with this library; if not, write to the Free Software
26 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
29 #include <urcu/uatomic.h>
36 void _cds_lfs_node_init_rcu(struct cds_lfs_node_rcu
*node
)
41 void _cds_lfs_init_rcu(struct cds_lfs_stack_rcu
*s
)
47 * Lock-free stack push is not subject to ABA problem, so no need to
48 * take the RCU read-side lock. Even if "head" changes between two
49 * uatomic_cmpxchg() invocations here (being popped, and then pushed
50 * again by one or more concurrent threads), the second
51 * uatomic_cmpxchg() invocation only cares about pushing a new entry at
52 * the head of the stack, ensuring consistency by making sure the new
53 * node->next is the same pointer value as the value replaced as head.
54 * It does not care about the content of the actual next node, so it can
55 * very well be reallocated between the two uatomic_cmpxchg().
57 * We take the approach of expecting the stack to be usually empty, so
58 * we first try an initial uatomic_cmpxchg() on a NULL old_head, and
59 * retry if the old head was non-NULL (the value read by the first
60 * uatomic_cmpxchg() is used as old head for the following loop). The
61 * upside of this scheme is to minimize the amount of cacheline traffic,
62 * always performing an exclusive cacheline access, rather than doing
63 * non-exclusive followed by exclusive cacheline access (which would be
64 * required if we first read the old head value). This design decision
65 * might be revisited after more throrough benchmarking on various
68 * Returns 0 if the stack was empty prior to adding the node.
69 * Returns non-zero otherwise.
72 int _cds_lfs_push_rcu(struct cds_lfs_stack_rcu
*s
,
73 struct cds_lfs_node_rcu
*node
)
75 struct cds_lfs_node_rcu
*head
= NULL
;
78 struct cds_lfs_node_rcu
*old_head
= head
;
82 * uatomic_cmpxchg() implicit memory barrier orders earlier
83 * stores to node before publication.
85 head
= uatomic_cmpxchg(&s
->head
, old_head
, node
);
89 return (int) !!((unsigned long) head
);
93 * Acts as a RCU reader.
95 * The caller must wait for a grace period to pass before freeing the returned
96 * node or modifying the cds_lfs_node_rcu structure.
97 * Returns NULL if stack is empty.
100 struct cds_lfs_node_rcu
*
101 _cds_lfs_pop_rcu(struct cds_lfs_stack_rcu
*s
)
104 struct cds_lfs_node_rcu
*head
;
107 head
= rcu_dereference(s
->head
);
109 struct cds_lfs_node_rcu
*next
= rcu_dereference(head
->next
);
111 if (uatomic_cmpxchg(&s
->head
, head
, next
) == head
) {
115 /* Concurrent modification. Retry. */
131 #endif /* _URCU_RCULFSTACK_STATIC_H */
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