/*
ChibiOS - Copyright (C) 2006..2018 Giovanni Di Sirio.
This file is part of ChibiOS.
ChibiOS 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 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/>.
*/
/**
* @file chsem.c
* @brief Semaphores code.
*
* @addtogroup semaphores
* @details Semaphores related APIs and services.
* <h2>Operation mode</h2>
* 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.<br>
* Operations defined for semaphores:
* - <b>Signal</b>: 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.
* - <b>Wait</b>: The semaphore counter is decreased and if the result
* becomes negative the thread is queued in the semaphore and
* suspended.
* - <b>Reset</b>: 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 for example.<br>
* Semaphores usually use a FIFO queuing strategy but it is possible
* to make them order threads by priority by enabling
* @p CH_CFG_USE_SEMAPHORES_PRIORITY in @p chconf.h.
* @pre In order to use the semaphore APIs the @p CH_CFG_USE_SEMAPHORES
* option must be enabled in @p chconf.h.
* @{
*/
#include "ch.h"
#if (CH_CFG_USE_SEMAPHORES == TRUE) || defined(__DOXYGEN__)
/*===========================================================================*/
/* Module exported variables. */
/*===========================================================================*/
/*===========================================================================*/
/* Module local types. */
/*===========================================================================*/
/*===========================================================================*/
/* Module local variables. */
/*===========================================================================*/
/*===========================================================================*/
/* Module local functions. */
/*===========================================================================*/
#if CH_CFG_USE_SEMAPHORES_PRIORITY == TRUE
#define sem_insert(tp, qp) queue_prio_insert(tp, qp)
#else
#define sem_insert(tp, qp) queue_insert(tp, qp)
#endif
/*===========================================================================*/
/* Module exported functions. */
/*===========================================================================*/
/**
* @brief Initializes a semaphore with the specified counter value.
*
* @param[out] sp pointer to a @p semaphore_t structure
* @param[in] n initial value of the semaphore counter. Must be
* non-negative.
*
* @init
*/
void chSemObjectInit(semaphore_t *sp, cnt_t n) {
chDbgCheck((sp != NULL) && (n >= (cnt_t)0));
queue_init(&sp->queue);
sp->cnt = n;
}
/**
* @brief Performs a reset operation on the semaphore.
* @post After invoking this function all the threads waiting on the
* semaphore, if any, are released and the semaphore counter is set
* to the specified, non negative, value.
* @note The released threads can recognize they were waked up by a reset
* rather than a signal because the @p chSemWait() will return
* @p MSG_RESET instead of @p MSG_OK.
*
* @param[in] sp pointer to a @p semaphore_t structure
* @param[in] n the new value of the semaphore counter. The value must
* be non-negative.
*
* @api
*/
void chSemReset(semaphore_t *sp, cnt_t n) {
chSysLock();
chSemResetI(sp, n);
chSchRescheduleS();
chSysUnlock();
}
/**
* @brief Performs a reset operation on the semaphore.
* @post After invoking this function all the threads waiting on the
* semaphore, if any, are released and the semaphore counter is set
* to the specified, non negative, value.
* @post This function does not reschedule so a call to a rescheduling
* function must be performed before unlocking the kernel. Note that
* interrupt handlers always reschedule on exit so an explicit
* reschedule must not be performed in ISRs.
* @note The released threads can recognize they were waked up by a reset
* rather than a signal because the @p chSemWait() will return
* @p MSG_RESET instead of @p MSG_OK.
*
* @param[in] sp pointer to a @p semaphore_t structure
* @param[in] n the new value of the semaphore counter. The value must
* be non-negative.
*
* @iclass
*/
void chSemResetI(semaphore_t *sp, cnt_t n) {
cnt_t cnt;
chDbgCheckClassI();
chDbgCheck((sp != NULL) && (n >= (cnt_t)0));
chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
"inconsistent semaphore");
cnt = sp->cnt;
sp->cnt = n;
while (++cnt <= (cnt_t)0) {
chSchReadyI(queue_lifo_remove(&sp->queue))->u.rdymsg = MSG_RESET;
}
}
/**
* @brief Performs a wait operation on a semaphore.
*
* @param[in] sp pointer to a @p semaphore_t structure
* @return A message specifying how the invoking thread has been
* released from the semaphore.
* @retval MSG_OK if the thread has not stopped on the semaphore or the
* semaphore has been signaled.
* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
*
* @api
*/
msg_t chSemWait(semaphore_t *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_t structure
* @return A message specifying how the invoking thread has been
* released from the semaphore.
* @retval MSG_OK if the thread has not stopped on the semaphore or the
* semaphore has been signaled.
* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
*
* @sclass
*/
msg_t chSemWaitS(semaphore_t *sp) {
chDbgCheckClassS();
chDbgCheck(sp != NULL);
chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
"inconsistent semaphore");
if (--sp->cnt < (cnt_t)0) {
currp->u.wtsemp = sp;
sem_insert(currp, &sp->queue);
chSchGoSleepS(CH_STATE_WTSEM);
return currp->u.rdymsg;
}
return MSG_OK;
}
/**
* @brief Performs a wait operation on a semaphore with timeout specification.
*
* @param[in] sp pointer to a @p semaphore_t structure
* @param[in] timeout the number of ticks before the operation timeouts,
* the following special values are allowed:
* - @a TIME_IMMEDIATE immediate timeout.
* - @a TIME_INFINITE no timeout.
* .
* @return A message specifying how the invoking thread has been
* released from the semaphore.
* @retval MSG_OK if the thread has not stopped on the semaphore or the
* semaphore has been signaled.
* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
* @retval MSG_TIMEOUT if the semaphore has not been signaled or reset within
* the specified timeout.
*
* @api
*/
msg_t chSemWaitTimeout(semaphore_t *sp, sysinterval_t timeout) {
msg_t msg;
chSysLock();
msg = chSemWaitTimeoutS(sp, timeout);
chSysUnlock();
return msg;
}
/**
* @brief Performs a wait operation on a semaphore with timeout specification.
*
* @param[in] sp pointer to a @p semaphore_t structure
* @param[in] timeout the number of ticks before the operation timeouts,
* the following special values are allowed:
* - @a TIME_IMMEDIATE immediate timeout.
* - @a TIME_INFINITE no timeout.
* .
* @return A message specifying how the invoking thread has been
* released from the semaphore.
* @retval MSG_OK if the thread has not stopped on the semaphore or the
* semaphore has been signaled.
* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
* @retval MSG_TIMEOUT if the semaphore has not been signaled or reset within
* the specified timeout.
*
* @sclass
*/
msg_t chSemWaitTimeoutS(semaphore_t *sp, sysinterval_t timeout) {
chDbgCheckClassS();
chDbgCheck(sp != NULL);
chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
"inconsistent semaphore");
if (--sp->cnt < (cnt_t)0) {
if (TIME_IMMEDIATE == timeout) {
sp->cnt++;
return MSG_TIMEOUT;
}
currp->u.wtsemp = sp;
sem_insert(currp, &sp->queue);
return chSchGoSleepTimeoutS(CH_STATE_WTSEM, timeout);
}
return MSG_OK;
}
/**
* @brief Performs a signal operation on a semaphore.
*
* @param[in] sp pointer to a @p semaphore_t structure
*
* @api
*/
void chSemSignal(semaphore_t *sp) {
chDbgCheck(sp != NULL);
chSysLock();
chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
"inconsistent semaphore");
if (++sp->cnt <= (cnt_t)0) {
chSchWakeupS(queue_fifo_remove(&sp->queue), MSG_OK);
}
chSysUnlock();
}
/**
* @brief Performs a signal operation on a semaphore.
* @post This function does not reschedule so a call to a rescheduling
* function must be performed before unlocking the kernel. Note that
* interrupt handlers always reschedule on exit so an explicit
* reschedule must not be performed in ISRs.
*
* @param[in] sp pointer to a @p semaphore_t structure
*
* @iclass
*/
void chSemSignalI(semaphore_t *sp) {
chDbgCheckClassI();
chDbgCheck(sp != NULL);
chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
"inconsistent semaphore");
if (++sp->cnt <= (cnt_t)0) {
/* Note, it is done this way in order to allow a tail call on
chSchReadyI().*/
thread_t *tp = queue_fifo_remove(&sp->queue);
tp->u.rdymsg = MSG_OK;
(void) chSchReadyI(tp);
}
}
/**
* @brief Adds the specified value to the semaphore counter.
* @post This function does not reschedule so a call to a rescheduling
* function must be performed before unlocking the kernel. Note that
* interrupt handlers always reschedule on exit so an explicit
* reschedule must not be performed in ISRs.
*
* @param[in] sp pointer to a @p semaphore_t structure
* @param[in] n value to be added to the semaphore counter. The value
* must be positive.
*
* @iclass
*/
void chSemAddCounterI(semaphore_t *sp, cnt_t n) {
chDbgCheckClassI();
chDbgCheck((sp != NULL) && (n > (cnt_t)0));
chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
"inconsistent semaphore");
while (n > (cnt_t)0) {
if (++sp->cnt <= (cnt_t)0) {
chSchReadyI(queue_fifo_remove(&sp->queue))->u.rdymsg = MSG_OK;
}
n--;
}
}
/**
* @brief Performs atomic signal and wait operations on two semaphores.
*
* @param[in] sps pointer to a @p semaphore_t structure to be signaled
* @param[in] spw pointer to a @p semaphore_t structure to wait on
* @return A message specifying how the invoking thread has been
* released from the semaphore.
* @retval MSG_OK if the thread has not stopped on the semaphore or the
* semaphore has been signaled.
* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
*
* @api
*/
msg_t chSemSignalWait(semaphore_t *sps, semaphore_t *spw) {
msg_t msg;
chDbgCheck((sps != NULL) && (spw != NULL));
chSysLock();
chDbgAssert(((sps->cnt >= (cnt_t)0) && queue_isempty(&sps->queue)) ||
((sps->cnt < (cnt_t)0) && queue_notempty(&sps->queue)),
"inconsistent semaphore");
chDbgAssert(((spw->cnt >= (cnt_t)0) && queue_isempty(&spw->queue)) ||
((spw->cnt < (cnt_t)0) && queue_notempty(&spw->queue)),
"inconsistent semaphore");
if (++sps->cnt <= (cnt_t)0) {
chSchReadyI(queue_fifo_remove(&sps->queue))->u.rdymsg = MSG_OK;
}
if (--spw->cnt < (cnt_t)0) {
thread_t *ctp = currp;
sem_insert(ctp, &spw->queue);
ctp->u.wtsemp = spw;
chSchGoSleepS(CH_STATE_WTSEM);
msg = ctp->u.rdymsg;
}
else {
chSchRescheduleS();
msg = MSG_OK;
}
chSysUnlock();
return msg;
}
#endif /* CH_CFG_USE_SEMAPHORES == TRUE */
/** @} */