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Diffstat (limited to 'nuttx/sched/sem_post.c')
| -rw-r--r-- | nuttx/sched/sem_post.c | 178 |
1 files changed, 178 insertions, 0 deletions
diff --git a/nuttx/sched/sem_post.c b/nuttx/sched/sem_post.c new file mode 100644 index 000000000..b3780db1f --- /dev/null +++ b/nuttx/sched/sem_post.c @@ -0,0 +1,178 @@ +/**************************************************************************** + * sched/sem_post.c + * + * Copyright (C) 2007-2009, 2012 Gregory Nutt. All rights reserved. + * Author: Gregory Nutt <gnutt@nuttx.org> + * + * 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 <nuttx/config.h> + +#include <limits.h> +#include <semaphore.h> +#include <sched.h> +#include <nuttx/arch.h> + +#include "os_internal.h" +#include "sem_internal.h" + +/**************************************************************************** + * Definitions + ****************************************************************************/ + +/**************************************************************************** + * Private Type Declarations + ****************************************************************************/ + +/**************************************************************************** + * Global Variables + ****************************************************************************/ + +/**************************************************************************** + * Private Variables + ****************************************************************************/ + +/**************************************************************************** + * Private Functions + ****************************************************************************/ + +/**************************************************************************** + * Public Functions + ****************************************************************************/ + +/**************************************************************************** + * 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 sem_wait(). + * + * Parameters: + * sem - Semaphore descriptor + * + * Return Value: + * 0 (OK) or -1 (ERROR) if unsuccessful + * + * Assumptions: + * This function cannot be called from an interrupt handler. + * It assumes the currently executing task is the one that + * is performing the unlock. + * + ****************************************************************************/ + +int sem_post(FAR sem_t *sem) +{ + FAR _TCB *stcb = NULL; + int ret = ERROR; + irqstate_t saved_state; + + /* Make sure we were supplied with a valid semaphore. */ + + if (sem) + { + /* The following operations must be performed with interrupts + * disabled because sem_post() may be called from an interrupt + * handler. + */ + + saved_state = irqsave(); + + /* Perform the semaphore unlock operation. */ + + ASSERT(sem->semcount < SEM_VALUE_MAX); + sem_releaseholder(sem); + sem->semcount++; + + /* If the result of of semaphore unlock is non-positive, then + * there must be some task waiting for the semaphore. + */ + +#ifdef CONFIG_PRIORITY_INHERITANCE + /* Don't let it run until we complete the priority restoration + * steps. + */ + + sched_lock(); +#endif + 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 _TCB*)g_waitingforsemaphore.head; + (stcb && stcb->waitsem != sem); + stcb = stcb->flink); + + if (stcb) + { + /* It is, let the task take the semaphore */ + + stcb->waitsem = NULL; + + /* Restart the waiting task. */ + + up_unblock_task(stcb); + } + } + + /* 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 + sem_restorebaseprio(stcb, sem); + sched_unlock(); +#endif + ret = OK; + + /* Interrupts may now be enabled. */ + + irqrestore(saved_state); + } + + return ret; +} |