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/*
ChibiOS/RT - Copyright (C) 2006-2007 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 <http://www.gnu.org/licenses/>.
*/
/**
* @addtogroup Semaphores
* @{
*/
#include <ch.h>
#ifdef CH_USE_SEMAPHORES
/**
* Initializes a semaphore with the specified counter value.
* @param sp pointer to a \p Semaphore structure
* @param n initial value of the semaphore counter. Must be non-negative.
* @note Can be called with interrupts disabled or enabled.
*/
void chSemInit(Semaphore *sp, cnt_t n) {
chDbgAssert(n >= 0, "chsem.c, chSemInit()");
fifo_init(&sp->s_queue);
sp->s_cnt = n;
}
/**
* Performs a reset operation on the semaphore.
* @param sp pointer to a \p Semaphore structure
* @param n the new value of the semaphore counter. The value must be non-negative.
* @note The released threads can recognize they were waked up by a reset
* instead than a signal because the \p chSemWait() will return
* \p RDY_RESET instead of \p RDY_OK.
*/
void chSemReset(Semaphore *sp, cnt_t n) {
chSysLock();
chSemResetI(sp, n);
chSchRescheduleS();
chSysUnlock();
}
/**
* Performs a reset operation on the semaphore.
* @param sp pointer to a \p Semaphore structure
* @param n the new value of the semaphore counter. The value must be non-negative.
* @note The released threads can recognize they were waked up by a reset
* instead than a signal because the \p chSemWait() will return
* \p RDY_RESET instead of \p RDY_OK.
* @note This function does not reschedule.
*/
void chSemResetI(Semaphore *sp, cnt_t n) {
cnt_t cnt;
chDbgAssert(n >= 0, "chsem.c, chSemResetI()");
cnt = sp->s_cnt;
sp->s_cnt = n;
while (cnt++ < 0)
chSchReadyI(lifo_remove(&sp->s_queue))->p_rdymsg = RDY_RESET;
}
/**
* Performs a wait operation on a semaphore.
* @param 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;
}
/**
* Performs a wait operation on a semaphore.
* @param 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().
* @note This function must be called with interrupts disabled.
* @note This function cannot be called by an interrupt handler.
*/
msg_t chSemWaitS(Semaphore *sp) {
if (--sp->s_cnt < 0) {
queue_insert(currp, &sp->s_queue);
currp->p_wtsemp = sp;
chSchGoSleepS(PRWTSEM);
return currp->p_rdymsg;
}
return RDY_OK;
}
#ifdef CH_USE_SEMAPHORES_TIMEOUT
/**
* Performs a wait operation on a semaphore with timeout specification.
* @param sp pointer to a \p Semaphore structure
* @param time the number of ticks before the operation fails
* @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.
* @note The function is available only if the \p CH_USE_SEMAPHORES_TIMEOUT
* option is enabled in \p chconf.h.
*/
msg_t chSemWaitTimeout(Semaphore *sp, systime_t time) {
msg_t msg;
chSysLock();
msg = chSemWaitTimeoutS(sp, time);
chSysUnlock();
return msg;
}
/**
* Performs a wait operation on a semaphore with timeout specification.
* @param sp pointer to a \p Semaphore structure
* @param time the number of ticks before the operation fails
* @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.
* @note The function is available only if the \p CH_USE_SEMAPHORES_TIMEOUT
* option is enabled in \p chconf.h.
*/
msg_t chSemWaitTimeoutS(Semaphore *sp, systime_t time) {
if (--sp->s_cnt < 0) {
queue_insert(currp, &sp->s_queue);
currp->p_wtsemp = sp;
return chSchGoSleepTimeoutS(PRWTSEM, time);
}
return RDY_OK;
}
#endif /* CH_USE_SEMAPHORES_TIMEOUT */
/**
* Performs a signal operation on a semaphore.
* @param sp pointer to a \p Semaphore structure
* @note The function is available only if the \p CH_USE_SEMAPHORES
* option is enabled in \p chconf.h.
*/
void chSemSignal(Semaphore *sp) {
chSysLock();
if (sp->s_cnt++ < 0)
chSchWakeupS(fifo_remove(&sp->s_queue), RDY_OK);
chSysUnlock();
}
/**
* Performs a signal operation on a semaphore.
* @param sp pointer to a \p Semaphore structure
* @note The function is available only if the \p CH_USE_SEMAPHORES
* option is enabled in \p chconf.h.
* @note This function does not reschedule.
*/
void chSemSignalI(Semaphore *sp) {
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_rdymsg = RDY_OK;
chSchReadyI(tp);
}
}
#ifdef CH_USE_SEMSW
/**
* Performs atomic signal and wait operations on two semaphores.
* @param sps pointer to a \p Semaphore structure to be signaled
* @param 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().
* @note The function is available only if the \p CH_USE_SEMSW
* option is enabled in \p chconf.h.
*/
msg_t chSemSignalWait(Semaphore *sps, Semaphore *spw) {
msg_t msg;
chSysLock();
if (sps->s_cnt++ < 0)
chSchReadyI(fifo_remove(&sps->s_queue))->p_rdymsg = RDY_OK;
if (--spw->s_cnt < 0) {
queue_insert(currp, &spw->s_queue);
currp->p_wtsemp = spw;
chSchGoSleepS(PRWTSEM);
msg = currp->p_rdymsg;
}
else {
chSchRescheduleS();
msg = RDY_OK;
}
chSysUnlock();
return msg;
}
#endif /* CH_USE_SEMSW */
#endif /* CH_USE_SEMAPHORES */
/** @} */
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