root / prex-0.9.0 / sys / sync / sem.c @ 03e9c04a
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1 | 03e9c04a | Brad Neuman | /*-
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2 | * Copyright (c) 2005-2007, Kohsuke Ohtani
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3 | * All rights reserved.
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4 | *
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5 | * Redistribution and use in source and binary forms, with or without
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6 | * modification, are permitted provided that the following conditions
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7 | * are met:
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8 | * 1. Redistributions of source code must retain the above copyright
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9 | * notice, this list of conditions and the following disclaimer.
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10 | * 2. Redistributions in binary form must reproduce the above copyright
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11 | * notice, this list of conditions and the following disclaimer in the
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12 | * documentation and/or other materials provided with the distribution.
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13 | * 3. Neither the name of the author nor the names of any co-contributors
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14 | * may be used to endorse or promote products derived from this software
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15 | * without specific prior written permission.
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16 | *
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17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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18 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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19 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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20 | * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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21 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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22 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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23 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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24 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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25 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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26 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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27 | * SUCH DAMAGE.
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28 | */
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29 | |||
30 | /*
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31 | * sem.c - semaphore support
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32 | */
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33 | |||
34 | #include <kernel.h> |
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35 | #include <event.h> |
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36 | #include <sched.h> |
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37 | #include <kmem.h> |
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38 | #include <task.h> |
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39 | #include <sync.h> |
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40 | |||
41 | /* forward declarations */
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42 | static int sem_valid(sem_t); |
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43 | static void sem_release(sem_t); |
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44 | static void sem_reference(sem_t); |
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45 | static int sem_copyin(sem_t *, sem_t *); |
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46 | |||
47 | static struct sem *sem_list = NULL; /* list head of semaphore list */ |
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48 | |||
49 | /*
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50 | * sem_init - initialize a semaphore; required before use.
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51 | *
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52 | * sem_init() creates a new semaphore if the specified
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53 | * semaphore does not exist yet. If the semaphore already
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54 | * exists, it is re-initialized only if nobody is waiting for
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55 | * it. The initial semaphore value is set to the requested
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56 | * value. A semaphore can be shared among different tasks.
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57 | */
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58 | int
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59 | sem_init(sem_t *sp, u_int value) |
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60 | { |
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61 | task_t self = curtask; |
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62 | sem_t s; |
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63 | |||
64 | /*
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65 | * A couple of quick sanity checks.
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66 | */
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67 | if (self->nsyncs >= MAXSYNCS)
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68 | return EAGAIN;
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69 | if (value > MAXSEMVAL)
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70 | return EINVAL;
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71 | if (copyin(sp, &s, sizeof(sp))) |
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72 | return EFAULT;
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73 | |||
74 | /*
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75 | * An application can call sem_init() to reset the
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76 | * value of existing semaphore. So, we have to check
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77 | * whether the semaphore is already allocated.
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78 | */
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79 | sched_lock(); |
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80 | if (sem_valid(s)) {
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81 | /*
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82 | * Semaphore already exists.
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83 | */
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84 | if (s->owner != self) {
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85 | sched_unlock(); |
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86 | return EINVAL;
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87 | } |
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88 | if (event_waiting(&s->event)) {
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89 | sched_unlock(); |
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90 | return EBUSY;
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91 | } |
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92 | s->value = value; |
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93 | |||
94 | } else {
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95 | /*
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96 | * Create new semaphore.
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97 | */
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98 | if ((s = kmem_alloc(sizeof(struct sem))) == NULL) { |
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99 | sched_unlock(); |
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100 | return ENOSPC;
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101 | } |
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102 | if (copyout(&s, sp, sizeof(s))) { |
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103 | kmem_free(s); |
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104 | sched_unlock(); |
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105 | return EFAULT;
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106 | } |
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107 | event_init(&s->event, "semaphore");
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108 | s->owner = self; |
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109 | s->refcnt = 1;
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110 | s->value = value; |
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111 | |||
112 | list_insert(&self->sems, &s->task_link); |
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113 | self->nsyncs++; |
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114 | s->next = sem_list; |
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115 | sem_list = s; |
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116 | } |
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117 | sched_unlock(); |
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118 | return 0; |
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119 | } |
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120 | |||
121 | /*
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122 | * Destroy a semaphore.
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123 | * If some thread is waiting for the specified semaphore,
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124 | * this routine fails with EBUSY.
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125 | */
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126 | int
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127 | sem_destroy(sem_t *sp) |
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128 | { |
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129 | sem_t s; |
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130 | |||
131 | sched_lock(); |
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132 | if (sem_copyin(sp, &s) || s->owner != curtask) {
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133 | sched_unlock(); |
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134 | return EINVAL;
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135 | } |
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136 | if (event_waiting(&s->event) || s->value == 0) { |
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137 | sched_unlock(); |
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138 | return EBUSY;
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139 | } |
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140 | sem_release(s); |
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141 | sched_unlock(); |
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142 | return 0; |
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143 | } |
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144 | |||
145 | /*
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146 | * sem_wait - lock a semaphore.
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147 | *
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148 | * The value of timeout is msec unit. 0 for no timeout.
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149 | *
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150 | * sem_wait() locks the semaphore referred by sem only if the
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151 | * semaphore value is currently positive. The thread will
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152 | * sleep while the semaphore value is zero. It decrements the
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153 | * semaphore value in return.
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154 | *
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155 | * If waiting thread receives any exception, this routine
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156 | * returns with EINTR in order to invoke exception
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157 | * handler. But, an application assumes this call does NOT
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158 | * return with an error. So, the system call stub routine will
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159 | * automatically call sem_wait again if it gets EINTR.
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160 | */
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161 | int
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162 | sem_wait(sem_t *sp, u_long timeout) |
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163 | { |
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164 | sem_t s; |
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165 | int rc, error = 0; |
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166 | |||
167 | sched_lock(); |
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168 | if (sem_copyin(sp, &s)) {
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169 | sched_unlock(); |
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170 | return EINVAL;
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171 | } |
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172 | sem_reference(s); |
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173 | |||
174 | while (s->value == 0) { |
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175 | rc = sched_tsleep(&s->event, timeout); |
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176 | if (rc == SLP_TIMEOUT) {
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177 | error = ETIMEDOUT; |
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178 | break;
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179 | } |
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180 | if (rc == SLP_INTR) {
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181 | error = EINTR; |
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182 | break;
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183 | } |
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184 | /*
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185 | * We have to check the semaphore value again
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186 | * because another thread may run and acquire
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187 | * the semaphore before us.
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188 | */
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189 | } |
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190 | if (!error)
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191 | s->value--; |
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192 | |||
193 | sem_release(s); |
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194 | sched_unlock(); |
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195 | return error;
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196 | } |
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197 | |||
198 | /*
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199 | * Try to lock a semaphore.
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200 | * If the semaphore is already locked, it just returns EAGAIN.
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201 | */
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202 | int
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203 | sem_trywait(sem_t *sp) |
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204 | { |
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205 | sem_t s; |
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206 | |||
207 | sched_lock(); |
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208 | if (sem_copyin(sp, &s)) {
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209 | sched_unlock(); |
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210 | return EINVAL;
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211 | } |
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212 | if (s->value == 0) { |
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213 | sched_unlock(); |
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214 | return EAGAIN;
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215 | } |
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216 | s->value--; |
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217 | sched_unlock(); |
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218 | return 0; |
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219 | } |
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220 | |||
221 | /*
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222 | * Unlock a semaphore.
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223 | *
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224 | * If the semaphore value becomes non zero, then one of
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225 | * the threads blocked waiting for the semaphore will be
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226 | * unblocked. This is non-blocking operation.
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227 | */
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228 | int
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229 | sem_post(sem_t *sp) |
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230 | { |
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231 | sem_t s; |
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232 | |||
233 | sched_lock(); |
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234 | if (sem_copyin(sp, &s)) {
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235 | sched_unlock(); |
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236 | return EINVAL;
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237 | } |
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238 | if (s->value >= MAXSEMVAL) {
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239 | sched_unlock(); |
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240 | return ERANGE;
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241 | } |
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242 | s->value++; |
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243 | if (s->value > 0) |
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244 | sched_wakeone(&s->event); |
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245 | |||
246 | sched_unlock(); |
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247 | return 0; |
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248 | } |
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249 | |||
250 | /*
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251 | * Get the semaphore value.
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252 | */
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253 | int
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254 | sem_getvalue(sem_t *sp, u_int *value) |
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255 | { |
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256 | sem_t s; |
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257 | |||
258 | sched_lock(); |
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259 | if (sem_copyin(sp, &s)) {
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260 | sched_unlock(); |
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261 | return EINVAL;
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262 | } |
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263 | if (copyout(&s->value, value, sizeof(s->value))) { |
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264 | sched_unlock(); |
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265 | return EFAULT;
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266 | } |
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267 | sched_unlock(); |
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268 | return 0; |
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269 | } |
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270 | |||
271 | /*
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272 | * Take out a reference on a semaphore.
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273 | */
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274 | static void |
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275 | sem_reference(sem_t s) |
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276 | { |
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277 | |||
278 | s->refcnt++; |
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279 | } |
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280 | |||
281 | /*
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282 | * Release a reference on a semaphore. If this is the last
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283 | * reference, the semaphore data structure is deallocated.
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284 | */
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285 | static void |
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286 | sem_release(sem_t s) |
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287 | { |
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288 | sem_t *sp; |
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289 | |||
290 | if (--s->refcnt > 0) |
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291 | return;
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292 | |||
293 | list_remove(&s->task_link); |
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294 | s->owner->nsyncs--; |
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295 | |||
296 | for (sp = &sem_list; *sp; sp = &(*sp)->next) {
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297 | if (*sp == s) {
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298 | *sp = s->next; |
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299 | break;
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300 | } |
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301 | } |
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302 | kmem_free(s); |
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303 | } |
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304 | |||
305 | void
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306 | sem_cleanup(task_t task) |
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307 | { |
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308 | list_t head, n; |
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309 | sem_t s; |
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310 | |||
311 | head = &task->sems; |
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312 | for (n = list_first(head); n != head; n = list_next(n)) {
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313 | s = list_entry(n, struct sem, task_link);
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314 | sem_release(s); |
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315 | } |
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316 | } |
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317 | |||
318 | static int |
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319 | sem_valid(sem_t s) |
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320 | { |
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321 | sem_t tmp; |
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322 | |||
323 | for (tmp = sem_list; tmp; tmp = tmp->next) {
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324 | if (tmp == s)
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325 | return 1; |
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326 | } |
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327 | return 0; |
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328 | } |
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329 | |||
330 | /*
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331 | * sem_copyin - copy a semaphore from user space.
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332 | *
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333 | * It also checks whether the passed semaphore is valid.
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334 | */
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335 | static int |
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336 | sem_copyin(sem_t *usp, sem_t *ksp) |
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337 | { |
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338 | sem_t s; |
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339 | |||
340 | if (copyin(usp, &s, sizeof(usp)) || !sem_valid(s)) |
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341 | return EINVAL;
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342 | |||
343 | *ksp = s; |
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344 | return 0; |
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345 | } |