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 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 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 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 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 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 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 } 104 105 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 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 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 } 147 148 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 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 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 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