/* ChibiOS/RT - Copyright (C) 2006,2007,2008,2009,2010 Giovanni Di Sirio. This file is part of ChibiOS/RT. ChibiOS/RT is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. ChibiOS/RT is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . */ /** * @file chsem.c * @brief Semaphores code. * * @addtogroup semaphores * @details Semaphores related APIs and services. * *

Operation mode

* Semaphores are a flexible synchronization primitive, ChibiOS/RT * implements semaphores in their "counting semaphores" variant as * defined by Edsger Dijkstra plus several enhancements like: * - Wait operation with timeout. * - Reset operation. * - Atomic wait+signal operation. * - Return message from the wait operation (OK, RESET, TIMEOUT). * . * The binary semaphores variant can be easily implemented using * counting semaphores.
* Operations defined for semaphores: * - Signal: The semaphore counter is increased and if the * result is non-positive then a waiting thread is removed from * the semaphore queue and made ready for execution. * - Wait: The semaphore counter is decreased and if the result * becomes negative the thread is queued in the semaphore and * suspended. * - Reset: The semaphore counter is reset to a non-negative * value and all the threads in the queue are released. * . * Semaphores can be used as guards for mutual exclusion zones * (note that mutexes are recommended for this kind of use) but * also have other uses, queues guards and counters as example.
* Semaphores usually use a FIFO queuing strategy but it is possible * to make them order threads by priority by enabling * @p CH_USE_SEMAPHORES_PRIORITY in @p chconf.h.
* In order to use the Semaphores APIs the @p CH_USE_SEMAPHORES * option must be enabled in @p chconf.h. * @{ */ #include "ch.h" #if CH_USE_SEMAPHORES #if CH_USE_SEMAPHORES_PRIORITY #define sem_insert(tp, qp) prio_insert(tp, qp) #else #define sem_insert(tp, qp) queue_insert(tp, qp) #endif /** * @brief Initializes a semaphore with the specified counter value. * * @param[out] sp pointer to a @p Semaphore structure * @param[in] n initial value of the semaphore counter. Must be * non-negative. */ void chSemInit(Semaphore *sp, cnt_t n) { chDbgCheck((sp != NULL) && (n >= 0), "chSemInit"); queue_init(&sp->s_queue); sp->s_cnt = n; } /** * @brief Performs a reset operation on the semaphore. * @note The released threads can recognize they were waked up by a reset * rather than a signal because the @p chSemWait() will return * @p RDY_RESET instead of @p RDY_OK. * * @param[in] sp pointer to a @p Semaphore structure * @param[in] n the new value of the semaphore counter. The value must * be non-negative. */ void chSemReset(Semaphore *sp, cnt_t n) { chSysLock(); chSemResetI(sp, n); chSchRescheduleS(); chSysUnlock(); } /** * @brief Performs a reset operation on the semaphore. * @note The released threads can recognize they were waked up by a reset * rather than a signal because the @p chSemWait() will return * @p RDY_RESET instead of @p RDY_OK. * @note This function does not reschedule. * * @param[in] sp pointer to a @p Semaphore structure * @param[in] n the new value of the semaphore counter. The value must * be non-negative. */ void chSemResetI(Semaphore *sp, cnt_t n) { cnt_t cnt; chDbgCheck((sp != NULL) && (n >= 0), "chSemResetI"); cnt = sp->s_cnt; sp->s_cnt = n; while (cnt++ < 0) chSchReadyI(lifo_remove(&sp->s_queue))->p_u.rdymsg = RDY_RESET; } /** * @brief Performs a wait operation on a semaphore. * * @param[in] sp pointer to a @p Semaphore structure * @retval RDY_OK if the semaphore was signaled or not taken. * @retval RDY_RESET if the semaphore was reset using @p chSemReset(). */ msg_t chSemWait(Semaphore *sp) { msg_t msg; chSysLock(); msg = chSemWaitS(sp); chSysUnlock(); return msg; } /** * @brief Performs a wait operation on a semaphore. * * @param[in] sp pointer to a @p Semaphore structure * @retval RDY_OK if the semaphore was signaled or not taken. * @retval RDY_RESET if the semaphore was reset using @p chSemReset(). */ msg_t chSemWaitS(Semaphore *sp) { chDbgCheck(sp != NULL, "chSemWaitS"); if (--sp->s_cnt < 0) { currp->p_u.wtobjp = sp; sem_insert(currp, &sp->s_queue); chSchGoSleepS(THD_STATE_WTSEM); return currp->p_u.rdymsg; } return RDY_OK; } /** * @brief Performs a wait operation on a semaphore with timeout specification. * * @param[in] sp pointer to a @p Semaphore structure * @param[in] time the number of ticks before the operation timeouts, * the following special values are allowed: * - @a TIME_IMMEDIATE immediate timeout. * - @a TIME_INFINITE no timeout. * . * @retval RDY_OK if the semaphore was signaled or not taken. * @retval RDY_RESET if the semaphore was reset using @p chSemReset(). * @retval RDY_TIMEOUT if the semaphore was not signaled or reset within the * specified timeout. */ msg_t chSemWaitTimeout(Semaphore *sp, systime_t time) { msg_t msg; chSysLock(); msg = chSemWaitTimeoutS(sp, time); chSysUnlock(); return msg; } /** * @brief Performs a wait operation on a semaphore with timeout specification. * * @param[in] sp pointer to a @p Semaphore structure * @param[in] time the number of ticks before the operation timeouts, * the following special values are allowed: * - @a TIME_IMMEDIATE immediate timeout. * - @a TIME_INFINITE no timeout. * . * @retval RDY_OK if the semaphore was signaled or not taken. * @retval RDY_RESET if the semaphore was reset using @p chSemReset(). * @retval RDY_TIMEOUT if the semaphore was not signaled or reset within the * specified timeout. */ msg_t chSemWaitTimeoutS(Semaphore *sp, systime_t time) { chDbgCheck(sp != NULL, "chSemWaitTimeoutS"); if (--sp->s_cnt < 0) { if (TIME_IMMEDIATE == time) { sp->s_cnt++; return RDY_TIMEOUT; } currp->p_u.wtobjp = sp; sem_insert(currp, &sp->s_queue); return chSchGoSleepTimeoutS(THD_STATE_WTSEM, time); } return RDY_OK; } /** * @brief Performs a signal operation on a semaphore. * * @param[in] sp pointer to a @p Semaphore structure */ void chSemSignal(Semaphore *sp) { chDbgCheck(sp != NULL, "chSemSignal"); chSysLock(); if (sp->s_cnt++ < 0) chSchWakeupS(fifo_remove(&sp->s_queue), RDY_OK); chSysUnlock(); } /** * @brief Performs a signal operation on a semaphore. * @note This function does not reschedule. * * @param[in] sp pointer to a @p Semaphore structure */ void chSemSignalI(Semaphore *sp) { chDbgCheck(sp != NULL, "chSemSignalI"); if (sp->s_cnt++ < 0) { /* note, it is done this way in order to allow a tail call on chSchReadyI().*/ Thread *tp = fifo_remove(&sp->s_queue); tp->p_u.rdymsg = RDY_OK; chSchReadyI(tp); } } #if CH_USE_SEMSW /** * @brief Performs atomic signal and wait operations on two semaphores. * @note The function is available only if the @p CH_USE_SEMSW * option is enabled in @p chconf.h. * * @param[in] sps pointer to a @p Semaphore structure to be signaled * @param[in] spw pointer to a @p Semaphore structure to be wait on * @retval RDY_OK if the semaphore was signaled or not taken. * @retval RDY_RESET if the semaphore was reset using @p chSemReset(). */ msg_t chSemSignalWait(Semaphore *sps, Semaphore *spw) { msg_t msg; chDbgCheck((sps != NULL) && (spw != NULL), "chSemSignalWait"); chSysLock(); if (sps->s_cnt++ < 0) chSchReadyI(fifo_remove(&sps->s_queue))->p_u.rdymsg = RDY_OK; if (--spw->s_cnt < 0) { Thread *ctp = currp; sem_insert(ctp, &spw->s_queue); ctp->p_u.wtobjp = spw; chSchGoSleepS(THD_STATE_WTSEM); msg = ctp->p_u.rdymsg; } else { chSchRescheduleS(); msg = RDY_OK; } chSysUnlock(); return msg; } #endif /* CH_USE_SEMSW */ #endif /* CH_USE_SEMAPHORES */ /** @} */ ref='#n167'>167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433