/usr/include/urcu/static/wfqueue.h is in liburcu-dev 0.7.12-0ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 | #ifndef _URCU_WFQUEUE_STATIC_H
#define _URCU_WFQUEUE_STATIC_H
/*
* wfqueue-static.h
*
* Userspace RCU library - Queue with Wait-Free Enqueue/Blocking Dequeue
*
* TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See wfqueue.h for linking
* dynamically with the userspace rcu library.
*
* Copyright 2010 - 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
* 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 <pthread.h>
#include <assert.h>
#include <poll.h>
#include <urcu/compiler.h>
#include <urcu/uatomic.h>
#ifdef __cplusplus
extern "C" {
#endif
/*
* Queue with wait-free enqueue/blocking dequeue.
* This implementation adds a dummy head node when the queue is empty to ensure
* we can always update the queue locklessly.
*
* Inspired from half-wait-free/half-blocking queue implementation done by
* Paul E. McKenney.
*/
#define WFQ_ADAPT_ATTEMPTS 10 /* Retry if being set */
#define WFQ_WAIT 10 /* Wait 10 ms if being set */
static inline void _cds_wfq_node_init(struct cds_wfq_node *node)
{
node->next = NULL;
}
static inline void _cds_wfq_init(struct cds_wfq_queue *q)
{
int ret;
_cds_wfq_node_init(&q->dummy);
/* Set queue head and tail */
q->head = &q->dummy;
q->tail = &q->dummy.next;
ret = pthread_mutex_init(&q->lock, NULL);
assert(!ret);
}
static inline void _cds_wfq_enqueue(struct cds_wfq_queue *q,
struct cds_wfq_node *node)
{
struct cds_wfq_node **old_tail;
/*
* uatomic_xchg() implicit memory barrier orders earlier stores to data
* structure containing node and setting node->next to NULL before
* publication.
*/
old_tail = uatomic_xchg(&q->tail, &node->next);
/*
* At this point, dequeuers see a NULL old_tail->next, which indicates
* that the queue is being appended to. The following store will append
* "node" to the queue from a dequeuer perspective.
*/
CMM_STORE_SHARED(*old_tail, node);
}
/*
* Waiting for enqueuer to complete enqueue and return the next node
*/
static inline struct cds_wfq_node *
___cds_wfq_node_sync_next(struct cds_wfq_node *node)
{
struct cds_wfq_node *next;
int attempt = 0;
/*
* Adaptative busy-looping waiting for enqueuer to complete enqueue.
*/
while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
if (++attempt >= WFQ_ADAPT_ATTEMPTS) {
poll(NULL, 0, WFQ_WAIT); /* Wait for 10ms */
attempt = 0;
} else
caa_cpu_relax();
}
return next;
}
/*
* It is valid to reuse and free a dequeued node immediately.
*
* No need to go on a waitqueue here, as there is no possible state in which the
* list could cause dequeue to busy-loop needlessly while waiting for another
* thread to be scheduled. The queue appears empty until tail->next is set by
* enqueue.
*/
static inline struct cds_wfq_node *
___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
{
struct cds_wfq_node *node, *next;
/*
* Queue is empty if it only contains the dummy node.
*/
if (q->head == &q->dummy && CMM_LOAD_SHARED(q->tail) == &q->dummy.next)
return NULL;
node = q->head;
next = ___cds_wfq_node_sync_next(node);
/*
* Move queue head forward.
*/
q->head = next;
/*
* Requeue dummy node if we just dequeued it.
*/
if (node == &q->dummy) {
_cds_wfq_node_init(node);
_cds_wfq_enqueue(q, node);
return ___cds_wfq_dequeue_blocking(q);
}
return node;
}
static inline struct cds_wfq_node *
_cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
{
struct cds_wfq_node *retnode;
int ret;
ret = pthread_mutex_lock(&q->lock);
assert(!ret);
retnode = ___cds_wfq_dequeue_blocking(q);
ret = pthread_mutex_unlock(&q->lock);
assert(!ret);
return retnode;
}
#ifdef __cplusplus
}
#endif
#endif /* _URCU_WFQUEUE_STATIC_H */
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