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406 lines
14 KiB
C
406 lines
14 KiB
C
4 years ago
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/*
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ChibiOS - Copyright (C) 2006..2018 Giovanni Di Sirio.
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This file is part of ChibiOS.
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ChibiOS is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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ChibiOS is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* @file rt/src/chsem.c
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* @brief Semaphores code.
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*
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* @addtogroup semaphores
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* @details Semaphores related APIs and services.
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* <h2>Operation mode</h2>
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* Semaphores are a flexible synchronization primitive, ChibiOS/RT
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* implements semaphores in their "counting semaphores" variant as
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* defined by Edsger Dijkstra plus several enhancements like:
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* - Wait operation with timeout.
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* - Reset operation.
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* - Atomic wait+signal operation.
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* - Return message from the wait operation (OK, RESET, TIMEOUT).
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* .
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* The binary semaphores variant can be easily implemented using
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* counting semaphores.<br>
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* Operations defined for semaphores:
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* - <b>Signal</b>: The semaphore counter is increased and if the
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* result is non-positive then a waiting thread is removed from
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* the semaphore queue and made ready for execution.
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* - <b>Wait</b>: The semaphore counter is decreased and if the result
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* becomes negative the thread is queued in the semaphore and
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* suspended.
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* - <b>Reset</b>: The semaphore counter is reset to a non-negative
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* value and all the threads in the queue are released.
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* .
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* Semaphores can be used as guards for mutual exclusion zones
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* (note that mutexes are recommended for this kind of use) but
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* also have other uses, queues guards and counters for example.<br>
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* Semaphores usually use a FIFO queuing strategy but it is possible
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* to make them order threads by priority by enabling
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* @p CH_CFG_USE_SEMAPHORES_PRIORITY in @p chconf.h.
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* @pre In order to use the semaphore APIs the @p CH_CFG_USE_SEMAPHORES
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* option must be enabled in @p chconf.h.
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* @{
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*/
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#include "ch.h"
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#if (CH_CFG_USE_SEMAPHORES == TRUE) || defined(__DOXYGEN__)
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/*===========================================================================*/
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/* Module exported variables. */
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/*===========================================================================*/
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/*===========================================================================*/
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/* Module local types. */
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/*===========================================================================*/
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/*===========================================================================*/
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/* Module local variables. */
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/*===========================================================================*/
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/*===========================================================================*/
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/* Module local functions. */
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/*===========================================================================*/
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#if CH_CFG_USE_SEMAPHORES_PRIORITY == TRUE
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#define sem_insert(tp, qp) queue_prio_insert(tp, qp)
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#else
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#define sem_insert(tp, qp) queue_insert(tp, qp)
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#endif
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/*===========================================================================*/
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/* Module exported functions. */
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/*===========================================================================*/
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/**
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* @brief Initializes a semaphore with the specified counter value.
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*
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* @param[out] sp pointer to a @p semaphore_t structure
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* @param[in] n initial value of the semaphore counter. Must be
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* non-negative.
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*
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* @init
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*/
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void chSemObjectInit(semaphore_t *sp, cnt_t n) {
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chDbgCheck((sp != NULL) && (n >= (cnt_t)0));
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queue_init(&sp->queue);
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sp->cnt = n;
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}
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/**
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* @brief Performs a reset operation on the semaphore.
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* @post After invoking this function all the threads waiting on the
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* semaphore, if any, are released and the semaphore counter is set
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* to the specified, non negative, value.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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* @param[in] n the new value of the semaphore counter. The value must
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* be non-negative.
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* @param[in] msg message to be sent
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*
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* @api
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*/
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void chSemResetWithMessage(semaphore_t *sp, cnt_t n, msg_t msg) {
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chSysLock();
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chSemResetWithMessageI(sp, n, msg);
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chSchRescheduleS();
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chSysUnlock();
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}
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/**
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* @brief Performs a reset operation on the semaphore.
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* @post After invoking this function all the threads waiting on the
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* semaphore, if any, are released and the semaphore counter is set
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* to the specified, non negative, value.
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* @post This function does not reschedule so a call to a rescheduling
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* function must be performed before unlocking the kernel. Note that
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* interrupt handlers always reschedule on exit so an explicit
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* reschedule must not be performed in ISRs.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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* @param[in] n the new value of the semaphore counter. The value must
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* be non-negative.
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* @param[in] msg message to be sent
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*
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* @iclass
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*/
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void chSemResetWithMessageI(semaphore_t *sp, cnt_t n, msg_t msg) {
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chDbgCheckClassI();
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chDbgCheck((sp != NULL) && (n >= (cnt_t)0));
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chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
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((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
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"inconsistent semaphore");
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sp->cnt = n;
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while (queue_notempty(&sp->queue)) {
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chSchReadyI(queue_lifo_remove(&sp->queue))->u.rdymsg = msg;
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}
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}
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/**
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* @brief Performs a wait operation on a semaphore.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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* @return A message specifying how the invoking thread has been
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* released from the semaphore.
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* @retval MSG_OK if the thread has not stopped on the semaphore or the
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* semaphore has been signaled.
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* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
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*
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* @api
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*/
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msg_t chSemWait(semaphore_t *sp) {
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msg_t msg;
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chSysLock();
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msg = chSemWaitS(sp);
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chSysUnlock();
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return msg;
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}
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/**
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* @brief Performs a wait operation on a semaphore.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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* @return A message specifying how the invoking thread has been
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* released from the semaphore.
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* @retval MSG_OK if the thread has not stopped on the semaphore or the
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* semaphore has been signaled.
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* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
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*
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* @sclass
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*/
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msg_t chSemWaitS(semaphore_t *sp) {
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chDbgCheckClassS();
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chDbgCheck(sp != NULL);
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chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
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((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
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"inconsistent semaphore");
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if (--sp->cnt < (cnt_t)0) {
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currp->u.wtsemp = sp;
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sem_insert(currp, &sp->queue);
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chSchGoSleepS(CH_STATE_WTSEM);
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return currp->u.rdymsg;
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}
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return MSG_OK;
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}
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/**
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* @brief Performs a wait operation on a semaphore with timeout specification.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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* @param[in] timeout the number of ticks before the operation timeouts,
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* the following special values are allowed:
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* - @a TIME_IMMEDIATE immediate timeout.
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* - @a TIME_INFINITE no timeout.
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* .
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* @return A message specifying how the invoking thread has been
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* released from the semaphore.
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* @retval MSG_OK if the thread has not stopped on the semaphore or the
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* semaphore has been signaled.
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* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
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* @retval MSG_TIMEOUT if the semaphore has not been signaled or reset within
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* the specified timeout.
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*
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* @api
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*/
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msg_t chSemWaitTimeout(semaphore_t *sp, sysinterval_t timeout) {
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msg_t msg;
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chSysLock();
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msg = chSemWaitTimeoutS(sp, timeout);
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chSysUnlock();
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return msg;
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}
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/**
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* @brief Performs a wait operation on a semaphore with timeout specification.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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* @param[in] timeout the number of ticks before the operation timeouts,
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* the following special values are allowed:
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* - @a TIME_IMMEDIATE immediate timeout.
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* - @a TIME_INFINITE no timeout.
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* .
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* @return A message specifying how the invoking thread has been
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* released from the semaphore.
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* @retval MSG_OK if the thread has not stopped on the semaphore or the
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* semaphore has been signaled.
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* @retval MSG_RESET if the semaphore has been reset using @p chSemReset().
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* @retval MSG_TIMEOUT if the semaphore has not been signaled or reset within
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* the specified timeout.
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*
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* @sclass
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*/
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msg_t chSemWaitTimeoutS(semaphore_t *sp, sysinterval_t timeout) {
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chDbgCheckClassS();
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chDbgCheck(sp != NULL);
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chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
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((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
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"inconsistent semaphore");
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if (--sp->cnt < (cnt_t)0) {
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if (TIME_IMMEDIATE == timeout) {
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sp->cnt++;
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return MSG_TIMEOUT;
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}
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currp->u.wtsemp = sp;
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sem_insert(currp, &sp->queue);
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return chSchGoSleepTimeoutS(CH_STATE_WTSEM, timeout);
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}
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return MSG_OK;
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}
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/**
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* @brief Performs a signal operation on a semaphore.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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*
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* @api
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*/
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void chSemSignal(semaphore_t *sp) {
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chDbgCheck(sp != NULL);
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chSysLock();
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chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
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((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
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"inconsistent semaphore");
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if (++sp->cnt <= (cnt_t)0) {
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chSchWakeupS(queue_fifo_remove(&sp->queue), MSG_OK);
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}
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chSysUnlock();
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}
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/**
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* @brief Performs a signal operation on a semaphore.
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* @post This function does not reschedule so a call to a rescheduling
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* function must be performed before unlocking the kernel. Note that
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* interrupt handlers always reschedule on exit so an explicit
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* reschedule must not be performed in ISRs.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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*
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* @iclass
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*/
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void chSemSignalI(semaphore_t *sp) {
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chDbgCheckClassI();
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chDbgCheck(sp != NULL);
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chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
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((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
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"inconsistent semaphore");
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if (++sp->cnt <= (cnt_t)0) {
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/* Note, it is done this way in order to allow a tail call on
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chSchReadyI().*/
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thread_t *tp = queue_fifo_remove(&sp->queue);
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tp->u.rdymsg = MSG_OK;
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(void) chSchReadyI(tp);
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}
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}
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/**
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* @brief Adds the specified value to the semaphore counter.
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* @post This function does not reschedule so a call to a rescheduling
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* function must be performed before unlocking the kernel. Note that
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* interrupt handlers always reschedule on exit so an explicit
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* reschedule must not be performed in ISRs.
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*
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* @param[in] sp pointer to a @p semaphore_t structure
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* @param[in] n value to be added to the semaphore counter. The value
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* must be positive.
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*
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* @iclass
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*/
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void chSemAddCounterI(semaphore_t *sp, cnt_t n) {
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chDbgCheckClassI();
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chDbgCheck((sp != NULL) && (n > (cnt_t)0));
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chDbgAssert(((sp->cnt >= (cnt_t)0) && queue_isempty(&sp->queue)) ||
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((sp->cnt < (cnt_t)0) && queue_notempty(&sp->queue)),
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"inconsistent semaphore");
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while (n > (cnt_t)0) {
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if (++sp->cnt <= (cnt_t)0) {
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chSchReadyI(queue_fifo_remove(&sp->queue))->u.rdymsg = MSG_OK;
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}
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n--;
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}
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}
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/**
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* @brief Performs atomic signal and wait operations on two semaphores.
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*
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* @param[in] sps pointer to a @p semaphore_t structure to be signaled
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||
|
|
* @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 */
|
||
|
|
|
||
|
|
/** @} */
|