/**************************************************************************** * sched/semaphore/sem_post.c * * Copyright (C) 2007-2009, 2012-2013, 2016-2017 Gregory Nutt. All rights * reserved. * Author: Gregory Nutt * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * 3. Neither the name NuttX nor the names of its contributors may be * used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * ****************************************************************************/ /**************************************************************************** * Included Files ****************************************************************************/ #include #include #include #include #include #include #include #include "sched/sched.h" #include "semaphore/semaphore.h" /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Name: nxsem_post * * Description: * When a kernel thread has finished with a semaphore, it will call * nxsem_post(). This function unlocks the semaphore referenced by sem * by performing the semaphore unlock operation on that semaphore. * * If the semaphore value resulting from this operation is positive, then * no tasks were blocked waiting for the semaphore to become unlocked; the * semaphore is simply incremented. * * If the value of the semaphore resulting from this operation is zero, * then one of the tasks blocked waiting for the semaphore shall be * allowed to return successfully from its call to nxsem_wait(). * * Input Parameters: * sem - Semaphore descriptor * * Returned Value: * This is an internal OS interface and should not be used by applications. * It follows the NuttX internal error return policy: Zero (OK) is * returned on success. A negated errno value is returned on failure. * * Assumptions: * This function may be called from an interrupt handler. * ****************************************************************************/ int nxsem_post(FAR sem_t *sem) { FAR struct tcb_s *stcb = NULL; irqstate_t flags; int ret = -EINVAL; /* Make sure we were supplied with a valid semaphore. */ if (sem != NULL) { /* The following operations must be performed with interrupts * disabled because sem_post() may be called from an interrupt * handler. */ flags = enter_critical_section(); /* Perform the semaphore unlock operation, releasing this task as a * holder then also incrementing the count on the semaphore. * * NOTE: When semaphores are used for signaling purposes, the holder * of the semaphore may not be this thread! In this case, * nxsem_releaseholder() will do nothing. * * In the case of a mutex this could be simply resolved since there is * only one holder but for the case of counting semaphores, there may * be many holders and if the holder is not this thread, then it is * not possible to know which thread/holder should be released. * * For this reason, it is recommended that priority inheritance be * disabled via nxsem_setprotocol(SEM_PRIO_NONE) when the semaphore is * initialized if the semaphore is to used for signaling purposes. */ DEBUGASSERT(sem->semcount < SEM_VALUE_MAX); nxsem_releaseholder(sem); sem->semcount++; #ifdef CONFIG_PRIORITY_INHERITANCE /* Don't let any unblocked tasks run until we complete any priority * restoration steps. Interrupts are disabled, but we do not want * the head of the read-to-run list to be modified yet. * * NOTE: If this sched_lock is called from an interrupt handler, it * will do nothing. */ sched_lock(); #endif /* If the result of of semaphore unlock is non-positive, then * there must be some task waiting for the semaphore. */ if (sem->semcount <= 0) { /* Check if there are any tasks in the waiting for semaphore * task list that are waiting for this semaphore. This is a * prioritized list so the first one we encounter is the one * that we want. */ for (stcb = (FAR struct tcb_s *)g_waitingforsemaphore.head; (stcb && stcb->waitsem != sem); stcb = stcb->flink); if (stcb != NULL) { /* The task will be the new holder of the semaphore when * it is awakened. */ nxsem_addholder_tcb(stcb, sem); /* It is, let the task take the semaphore */ stcb->waitsem = NULL; /* Restart the waiting task. */ up_unblock_task(stcb); } #if 0 /* REVISIT: This can fire on IOB throttle semaphore */ else { /* This should not happen. */ DEBUGPANIC(); } #endif } /* Check if we need to drop the priority of any threads holding * this semaphore. The priority could have been boosted while they * held the semaphore. */ #ifdef CONFIG_PRIORITY_INHERITANCE nxsem_restorebaseprio(stcb, sem); sched_unlock(); #endif ret = OK; /* Interrupts may now be enabled. */ leave_critical_section(flags); } return ret; } /**************************************************************************** * Name: sem_post * * Description: * When a task has finished with a semaphore, it will call sem_post(). * This function unlocks the semaphore referenced by sem by performing the * semaphore unlock operation on that semaphore. * * If the semaphore value resulting from this operation is positive, then * no tasks were blocked waiting for the semaphore to become unlocked; the * semaphore is simply incremented. * * If the value of the semaphore resulting from this operation is zero, * then one of the tasks blocked waiting for the semaphore shall be * allowed to return successfully from its call to nxsem_wait(). * * Input Parameters: * sem - Semaphore descriptor * * Returned Value: * This function is a standard, POSIX application interface. It will * return zero (OK) if successful. Otherwise, -1 (ERROR) is returned and * the errno value is set appropriately. * * Assumptions: * This function may be called from an interrupt handler. * ****************************************************************************/ int sem_post(FAR sem_t *sem) { int ret; ret = nxsem_post(sem); if (ret < 0) { set_errno(-ret); ret = ERROR; } return ret; }