1/*
2 * Copyright 2010-2015 Samy Al Bahra.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27#ifndef CK_SEQUENCE_H
28#define CK_SEQUENCE_H
29
30#include <ck_cc.h>
31#include <ck_pr.h>
32#include <ck_stdbool.h>
33
34struct ck_sequence {
35	unsigned int sequence;
36};
37typedef struct ck_sequence ck_sequence_t;
38
39#define CK_SEQUENCE_INITIALIZER { .sequence = 0 }
40
41CK_CC_INLINE static void
42ck_sequence_init(struct ck_sequence *sq)
43{
44
45	ck_pr_store_uint(&sq->sequence, 0);
46	return;
47}
48
49CK_CC_INLINE static unsigned int
50ck_sequence_read_begin(const struct ck_sequence *sq)
51{
52	unsigned int version;
53
54	for (;;) {
55		version = ck_pr_load_uint(&sq->sequence);
56
57		/*
58		 * If a sequence is even then associated data may be in a
59		 * consistent state.
60		 */
61		if (CK_CC_LIKELY((version & 1) == 0))
62			break;
63
64		/*
65		 * If a sequence is odd then a thread is in the middle of an
66		 * update. Retry the read to avoid operating on inconsistent
67		 * data.
68		 */
69		ck_pr_stall();
70	}
71
72	ck_pr_fence_load();
73	return version;
74}
75
76CK_CC_INLINE static bool
77ck_sequence_read_retry(const struct ck_sequence *sq, unsigned int version)
78{
79
80	/*
81	 * If the sequence number was updated then a read should be
82	 * re-attempted.
83	 */
84	ck_pr_fence_load();
85	return ck_pr_load_uint(&sq->sequence) != version;
86}
87
88#define CK_SEQUENCE_READ(seqlock, version) 						\
89	for (*(version) = 1;								\
90	    (*(version) != 0) && (*(version) = ck_sequence_read_begin(seqlock), 1);	\
91	    *(version) = ck_sequence_read_retry(seqlock, *(version)))
92
93/*
94 * This must be called after a successful mutex acquisition.
95 */
96CK_CC_INLINE static void
97ck_sequence_write_begin(struct ck_sequence *sq)
98{
99
100	/*
101	 * Increment the sequence to an odd number to indicate
102	 * the beginning of a write update.
103	 */
104	ck_pr_store_uint(&sq->sequence, sq->sequence + 1);
105	ck_pr_fence_store();
106	return;
107}
108
109/*
110 * This must be called before mutex ownership is relinquished.
111 */
112CK_CC_INLINE static void
113ck_sequence_write_end(struct ck_sequence *sq)
114{
115
116	/*
117	 * Increment the sequence to an even number to indicate
118	 * completion of a write update.
119	 */
120	ck_pr_fence_store();
121	ck_pr_store_uint(&sq->sequence, sq->sequence + 1);
122	return;
123}
124
125#endif /* CK_SEQUENCE_H */
126