1 | /*
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2 | * Copyright (c) 2001-2004 Jakub Jermar
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3 | * Copyright (c) 2025 Jiří Zárevúcky
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4 | * All rights reserved.
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5 | *
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6 | * Redistribution and use in source and binary forms, with or without
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7 | * modification, are permitted provided that the following conditions
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8 | * are met:
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9 | *
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10 | * - Redistributions of source code must retain the above copyright
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11 | * notice, this list of conditions and the following disclaimer.
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12 | * - Redistributions in binary form must reproduce the above copyright
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13 | * notice, this list of conditions and the following disclaimer in the
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14 | * documentation and/or other materials provided with the distribution.
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15 | * - The name of the author may not be used to endorse or promote products
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16 | * derived from this software without specific prior written permission.
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17 | *
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18 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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19 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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20 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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21 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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22 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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23 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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24 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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25 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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26 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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27 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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28 | */
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29 |
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30 | /** @addtogroup kernel_sync
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31 | * @{
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32 | */
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33 |
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34 | /**
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35 | * @file
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36 | * @brief Mutexes.
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37 | */
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38 |
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39 | #include <assert.h>
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40 | #include <errno.h>
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41 | #include <proc/thread.h>
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42 | #include <stdatomic.h>
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43 | #include <synch/mutex.h>
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44 | #include <synch/semaphore.h>
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45 |
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46 | /** Initialize mutex.
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47 | *
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48 | * @param mtx Mutex.
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49 | * @param type Type of the mutex.
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50 | */
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51 | void mutex_initialize(mutex_t *mtx, mutex_type_t type)
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52 | {
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53 | *mtx = MUTEX_INITIALIZER(*mtx, type);
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54 | }
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55 |
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56 | /** A race in mtx->owner access is unavoidable, so we have to make
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57 | * access to it formally atomic. These are convenience functions to
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58 | * read/write the variable without memory barriers, since we don't need
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59 | * them and C11 atomics default to the strongest possible memory ordering
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60 | * by default, which is utterly ridiculous.
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61 | */
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62 | static inline thread_t *_get_owner(mutex_t *mtx)
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63 | {
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64 | return atomic_load_explicit(&mtx->owner, memory_order_relaxed);
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65 | }
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66 |
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67 | /** Counterpart to _get_owner(). */
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68 | static inline void _set_owner(mutex_t *mtx, thread_t *owner)
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69 | {
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70 | atomic_store_explicit(&mtx->owner, owner, memory_order_relaxed);
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71 | }
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72 |
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73 | /** Find out whether the mutex is currently locked.
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74 | *
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75 | * @param mtx Mutex.
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76 | *
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77 | * @return True if the mutex is locked, false otherwise.
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78 | */
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79 | bool mutex_locked(mutex_t *mtx)
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80 | {
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81 | if (!THREAD)
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82 | return mtx->nesting > 0;
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83 |
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84 | return _get_owner(mtx) == THREAD;
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85 | }
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86 |
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87 | /** Acquire mutex.
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88 | *
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89 | * This operation is uninterruptible and cannot fail.
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90 | */
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91 | void mutex_lock(mutex_t *mtx)
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92 | {
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93 | if (!THREAD) {
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94 | assert(mtx->type == MUTEX_RECURSIVE || mtx->nesting == 0);
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95 | mtx->nesting++;
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96 | return;
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97 | }
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98 |
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99 | if (_get_owner(mtx) == THREAD) {
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100 | /* This will also detect nested locks on a non-recursive mutex. */
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101 | assert(mtx->type == MUTEX_RECURSIVE);
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102 | assert(mtx->nesting > 0);
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103 | mtx->nesting++;
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104 | return;
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105 | }
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106 |
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107 | semaphore_down(&mtx->sem);
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108 |
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109 | _set_owner(mtx, THREAD);
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110 | assert(mtx->nesting == 0);
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111 | mtx->nesting = 1;
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112 | }
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113 |
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114 | /** Acquire mutex with timeout.
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115 | *
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116 | * @param mtx Mutex.
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117 | * @param usec Timeout in microseconds.
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118 | *
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119 | * @return EOK if lock was successfully acquired, something else otherwise.
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120 | */
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121 | errno_t mutex_lock_timeout(mutex_t *mtx, uint32_t usec)
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122 | {
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123 | if (!THREAD) {
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124 | assert(mtx->type == MUTEX_RECURSIVE || mtx->nesting == 0);
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125 | mtx->nesting++;
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126 | return EOK;
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127 | }
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128 |
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129 | if (_get_owner(mtx) == THREAD) {
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130 | assert(mtx->type == MUTEX_RECURSIVE);
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131 | assert(mtx->nesting > 0);
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132 | mtx->nesting++;
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133 | return EOK;
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134 | }
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135 |
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136 | errno_t rc = semaphore_down_timeout(&mtx->sem, usec);
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137 | if (rc != EOK)
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138 | return rc;
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139 |
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140 | _set_owner(mtx, THREAD);
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141 | assert(mtx->nesting == 0);
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142 | mtx->nesting = 1;
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143 | return EOK;
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144 | }
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145 |
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146 | /** Attempt to acquire mutex without blocking.
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147 | *
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148 | * @return EOK if lock was successfully acquired, something else otherwise.
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149 | */
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150 | errno_t mutex_trylock(mutex_t *mtx)
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151 | {
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152 | return mutex_lock_timeout(mtx, 0);
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153 | }
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154 |
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155 | /** Release mutex.
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156 | *
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157 | * @param mtx Mutex.
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158 | */
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159 | void mutex_unlock(mutex_t *mtx)
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160 | {
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161 | if (--mtx->nesting > 0) {
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162 | assert(mtx->type == MUTEX_RECURSIVE);
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163 | return;
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164 | }
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165 |
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166 | assert(mtx->nesting == 0);
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167 |
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168 | if (!THREAD)
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169 | return;
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170 |
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171 | assert(_get_owner(mtx) == THREAD);
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172 | _set_owner(mtx, NULL);
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173 |
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174 | semaphore_up(&mtx->sem);
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175 | }
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176 |
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177 | /** @}
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178 | */
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