1 /*
2 * Copyright 2014 Jaidev Sridhar.
3 * Copyright 2014 Samy Al Bahra.
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28 #ifndef CK_SWLOCK_H
29 #define CK_SWLOCK_H
30
31 #include <ck_elide.h>
32 #include <ck_limits.h>
33 #include <ck_pr.h>
34 #include <ck_stdbool.h>
35 #include <ck_stddef.h>
36
37 struct ck_swlock {
38 uint32_t value;
39 };
40 typedef struct ck_swlock ck_swlock_t;
41
42 #define CK_SWLOCK_INITIALIZER {0}
43 #define CK_SWLOCK_WRITER_BIT (1UL << 31)
44 #define CK_SWLOCK_LATCH_BIT (1UL << 30)
45 #define CK_SWLOCK_WRITER_MASK (CK_SWLOCK_LATCH_BIT | CK_SWLOCK_WRITER_BIT)
46 #define CK_SWLOCK_READER_MASK (UINT32_MAX ^ CK_SWLOCK_WRITER_MASK)
47
48 CK_CC_INLINE static void
ck_swlock_init(struct ck_swlock * rw)49 ck_swlock_init(struct ck_swlock *rw)
50 {
51
52 rw->value = 0;
53 ck_pr_barrier();
54 return;
55 }
56
57 CK_CC_INLINE static void
ck_swlock_write_unlock(ck_swlock_t * rw)58 ck_swlock_write_unlock(ck_swlock_t *rw)
59 {
60
61 ck_pr_fence_unlock();
62 ck_pr_and_32(&rw->value, CK_SWLOCK_READER_MASK);
63 return;
64 }
65
66 CK_CC_INLINE static bool
ck_swlock_locked_writer(ck_swlock_t * rw)67 ck_swlock_locked_writer(ck_swlock_t *rw)
68 {
69 bool r;
70
71 r = ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT;
72 ck_pr_fence_acquire();
73 return r;
74 }
75
76 CK_CC_INLINE static void
ck_swlock_write_downgrade(ck_swlock_t * rw)77 ck_swlock_write_downgrade(ck_swlock_t *rw)
78 {
79
80 ck_pr_inc_32(&rw->value);
81 ck_swlock_write_unlock(rw);
82 return;
83 }
84
85 CK_CC_INLINE static bool
ck_swlock_locked(ck_swlock_t * rw)86 ck_swlock_locked(ck_swlock_t *rw)
87 {
88 bool r;
89
90 r = ck_pr_load_32(&rw->value);
91 ck_pr_fence_acquire();
92 return r;
93 }
94
95 CK_CC_INLINE static bool
ck_swlock_write_trylock(ck_swlock_t * rw)96 ck_swlock_write_trylock(ck_swlock_t *rw)
97 {
98 bool r;
99
100 r = ck_pr_cas_32(&rw->value, 0, CK_SWLOCK_WRITER_BIT);
101 ck_pr_fence_lock();
102 return r;
103 }
104
CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_write,ck_swlock_t,ck_swlock_locked,ck_swlock_write_trylock)105 CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_write, ck_swlock_t,
106 ck_swlock_locked, ck_swlock_write_trylock)
107
108 CK_CC_INLINE static void
109 ck_swlock_write_lock(ck_swlock_t *rw)
110 {
111
112 ck_pr_or_32(&rw->value, CK_SWLOCK_WRITER_BIT);
113 while (ck_pr_load_32(&rw->value) & CK_SWLOCK_READER_MASK)
114 ck_pr_stall();
115
116 ck_pr_fence_lock();
117 return;
118 }
119
120 CK_CC_INLINE static void
ck_swlock_write_latch(ck_swlock_t * rw)121 ck_swlock_write_latch(ck_swlock_t *rw)
122 {
123
124 /* Publish intent to acquire lock. */
125 ck_pr_or_32(&rw->value, CK_SWLOCK_WRITER_BIT);
126
127 /* Stall until readers have seen the writer and cleared. */
128 while (ck_pr_cas_32(&rw->value, CK_SWLOCK_WRITER_BIT,
129 CK_SWLOCK_WRITER_MASK) == false) {
130 do {
131 ck_pr_stall();
132 } while (ck_pr_load_32(&rw->value) != CK_SWLOCK_WRITER_BIT);
133 }
134
135 ck_pr_fence_lock();
136 return;
137 }
138
139 CK_CC_INLINE static void
ck_swlock_write_unlatch(ck_swlock_t * rw)140 ck_swlock_write_unlatch(ck_swlock_t *rw)
141 {
142
143 ck_pr_fence_unlock();
144 ck_pr_store_32(&rw->value, 0);
145 return;
146 }
147
CK_ELIDE_PROTOTYPE(ck_swlock_write,ck_swlock_t,ck_swlock_locked,ck_swlock_write_lock,ck_swlock_locked_writer,ck_swlock_write_unlock)148 CK_ELIDE_PROTOTYPE(ck_swlock_write, ck_swlock_t,
149 ck_swlock_locked, ck_swlock_write_lock,
150 ck_swlock_locked_writer, ck_swlock_write_unlock)
151
152 CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_read, ck_swlock_t,
153 ck_swlock_locked_writer, ck_swlock_read_trylock)
154
155 CK_CC_INLINE static bool
156 ck_swlock_read_trylock(ck_swlock_t *rw)
157 {
158 uint32_t l = ck_pr_load_32(&rw->value);
159
160 if (l & CK_SWLOCK_WRITER_BIT)
161 return false;
162
163 l = ck_pr_faa_32(&rw->value, 1) & CK_SWLOCK_WRITER_MASK;
164 if (l == CK_SWLOCK_WRITER_BIT)
165 ck_pr_dec_32(&rw->value);
166
167 ck_pr_fence_lock();
168 return l == 0;
169 }
170
171 CK_CC_INLINE static void
ck_swlock_read_lock(ck_swlock_t * rw)172 ck_swlock_read_lock(ck_swlock_t *rw)
173 {
174 uint32_t l;
175
176 for (;;) {
177 while (ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT)
178 ck_pr_stall();
179
180 l = ck_pr_faa_32(&rw->value, 1) & CK_SWLOCK_WRITER_MASK;
181 if (l == 0)
182 break;
183
184 /*
185 * If the latch bit has not been set, then the writer would
186 * have observed the reader and will wait to completion of
187 * read-side critical section.
188 */
189 if (l == CK_SWLOCK_WRITER_BIT)
190 ck_pr_dec_32(&rw->value);
191 }
192
193 ck_pr_fence_lock();
194 return;
195 }
196
197 CK_CC_INLINE static bool
ck_swlock_locked_reader(ck_swlock_t * rw)198 ck_swlock_locked_reader(ck_swlock_t *rw)
199 {
200
201 ck_pr_fence_load();
202 return ck_pr_load_32(&rw->value) & CK_SWLOCK_READER_MASK;
203 }
204
205 CK_CC_INLINE static void
ck_swlock_read_unlock(ck_swlock_t * rw)206 ck_swlock_read_unlock(ck_swlock_t *rw)
207 {
208
209 ck_pr_fence_unlock();
210 ck_pr_dec_32(&rw->value);
211 return;
212 }
213
214 CK_ELIDE_PROTOTYPE(ck_swlock_read, ck_swlock_t,
215 ck_swlock_locked_writer, ck_swlock_read_lock,
216 ck_swlock_locked_reader, ck_swlock_read_unlock)
217
218 #endif /* CK_SWLOCK_H */
219