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
34 struct ck_sequence {
35 unsigned int sequence;
36 };
37 typedef struct ck_sequence ck_sequence_t;
38
39 #define CK_SEQUENCE_INITIALIZER { .sequence = 0 }
40
41 CK_CC_INLINE static void
ck_sequence_init(struct ck_sequence * sq)42 ck_sequence_init(struct ck_sequence *sq)
43 {
44
45 ck_pr_store_uint(&sq->sequence, 0);
46 return;
47 }
48
49 CK_CC_INLINE static unsigned int
ck_sequence_read_begin(const struct ck_sequence * sq)50 ck_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
76 CK_CC_INLINE static bool
ck_sequence_read_retry(const struct ck_sequence * sq,unsigned int version)77 ck_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 */
96 CK_CC_INLINE static void
ck_sequence_write_begin(struct ck_sequence * sq)97 ck_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 */
112 CK_CC_INLINE static void
ck_sequence_write_end(struct ck_sequence * sq)113 ck_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