2 * Copyright 2014 Jaidev Sridhar.
3 * Copyright 2014 Samy Al Bahra.
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
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.
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
32 #include <ck_limits.h>
34 #include <ck_stdbool.h>
35 #include <ck_stddef.h>
40 typedef struct ck_swlock ck_swlock_t;
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)
48 CK_CC_INLINE static void
49 ck_swlock_init(struct ck_swlock *rw)
57 CK_CC_INLINE static void
58 ck_swlock_write_unlock(ck_swlock_t *rw)
62 ck_pr_and_32(&rw->value, CK_SWLOCK_READER_MASK);
66 CK_CC_INLINE static bool
67 ck_swlock_locked_writer(ck_swlock_t *rw)
71 r = ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT;
72 ck_pr_fence_acquire();
76 CK_CC_INLINE static void
77 ck_swlock_write_downgrade(ck_swlock_t *rw)
80 ck_pr_inc_32(&rw->value);
81 ck_swlock_write_unlock(rw);
85 CK_CC_INLINE static bool
86 ck_swlock_locked(ck_swlock_t *rw)
90 r = ck_pr_load_32(&rw->value);
91 ck_pr_fence_acquire();
95 CK_CC_INLINE static bool
96 ck_swlock_write_trylock(ck_swlock_t *rw)
100 r = ck_pr_cas_32(&rw->value, 0, CK_SWLOCK_WRITER_BIT);
105 CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_write, ck_swlock_t,
106 ck_swlock_locked, ck_swlock_write_trylock)
108 CK_CC_INLINE static void
109 ck_swlock_write_lock(ck_swlock_t *rw)
112 ck_pr_or_32(&rw->value, CK_SWLOCK_WRITER_BIT);
113 while (ck_pr_load_32(&rw->value) & CK_SWLOCK_READER_MASK)
120 CK_CC_INLINE static void
121 ck_swlock_write_latch(ck_swlock_t *rw)
124 /* Publish intent to acquire lock. */
125 ck_pr_or_32(&rw->value, CK_SWLOCK_WRITER_BIT);
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) {
132 } while (ck_pr_load_32(&rw->value) != CK_SWLOCK_WRITER_BIT);
139 CK_CC_INLINE static void
140 ck_swlock_write_unlatch(ck_swlock_t *rw)
143 ck_pr_fence_unlock();
144 ck_pr_store_32(&rw->value, 0);
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)
152 CK_ELIDE_TRYLOCK_PROTOTYPE(ck_swlock_read, ck_swlock_t,
153 ck_swlock_locked_writer, ck_swlock_read_trylock)
155 CK_CC_INLINE static bool
156 ck_swlock_read_trylock(ck_swlock_t *rw)
158 uint32_t l = ck_pr_load_32(&rw->value);
160 if (l & CK_SWLOCK_WRITER_BIT)
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);
171 CK_CC_INLINE static void
172 ck_swlock_read_lock(ck_swlock_t *rw)
177 while (ck_pr_load_32(&rw->value) & CK_SWLOCK_WRITER_BIT)
180 l = ck_pr_faa_32(&rw->value, 1) & CK_SWLOCK_WRITER_MASK;
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.
189 if (l == CK_SWLOCK_WRITER_BIT)
190 ck_pr_dec_32(&rw->value);
197 CK_CC_INLINE static bool
198 ck_swlock_locked_reader(ck_swlock_t *rw)
202 return ck_pr_load_32(&rw->value) & CK_SWLOCK_READER_MASK;
205 CK_CC_INLINE static void
206 ck_swlock_read_unlock(ck_swlock_t *rw)
209 ck_pr_fence_unlock();
210 ck_pr_dec_32(&rw->value);
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)
218 #endif /* CK_SWLOCK_H */