1 #ifndef _URCU_RCUWFSTACK_H
2 #define _URCU_RCUWFSTACK_H
7 * Userspace RCU library - RCU Stack with Wait-Free push, Blocking pop.
9 * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
11 * This library is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU Lesser General Public
13 * License as published by the Free Software Foundation; either
14 * version 2.1 of the License, or (at your option) any later version.
16 * This library is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * Lesser General Public License for more details.
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this library; if not, write to the Free Software
23 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
28 #if (!defined(_GNU_SOURCE) && !defined(_LGPL_SOURCE))
29 #error "Dynamic loader LGPL wrappers not implemented yet"
32 #define RCU_WF_STACK_END ((void *)0x1UL)
35 struct rcu_wfs_node
*next
;
38 struct rcu_wfs_stack
{
39 struct rcu_wfs_node
*head
;
42 void rcu_wfs_node_init(struct rcu_wfs_node
*node
)
47 void rcu_wfs_init(struct rcu_wfs_stack
*s
)
49 s
->head
= RCU_WF_STACK_END
;
52 void rcu_wfs_push(struct rcu_wfs_stack
*s
, struct rcu_wfs_node
*node
)
54 struct rcu_wfs_node
*old_head
;
56 assert(node
->next
== NULL
);
58 * uatomic_xchg() implicit memory barrier orders earlier stores to node
59 * (setting it to NULL) before publication.
61 old_head
= uatomic_xchg(&s
->head
, node
);
63 * At this point, dequeuers see a NULL node->next, they should busy-wait
64 * until node->next is set to old_head.
66 STORE_SHARED(node
->next
, old_head
);
70 * The caller must wait for a grace period before:
71 * - freeing the returned node.
72 * - modifying the ->next pointer of the returned node. (be careful with unions)
73 * - passing the returned node back to push() on the same stack they got it
76 * Returns NULL if stack is empty.
78 * cmpxchg is protected from ABA races by holding a RCU read lock between
79 * s->head read and cmpxchg modifying s->head and requiring that dequeuers wait
80 * for a grace period before freeing the returned node.
82 * TODO: implement adaptative busy-wait and wait/wakeup scheme rather than busy
83 * loops. Better for UP.
86 rcu_wfs_pop_blocking(struct rcu_wfs_stack
*s
)
89 struct rcu_wfs_node
*head
;
92 head
= rcu_dereference(s
->head
);
93 if (head
!= RCU_WF_STACK_END
) {
94 struct rcu_wfs_node
*next
= rcu_dereference(head
->next
);
96 /* Retry while head is being set by push(). */
101 if (uatomic_cmpxchg(&s
->head
, head
, next
) == head
) {
105 /* Concurrent modification. Retry. */
117 #endif /* _URCU_RCUWFSTACK_H */
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