/**************************************************************************** * sched/sem_trywait.c * * Copyright (C) 2007-2009 Gregory Nutt. All rights reserved. * Author: Gregory Nutt <spudmonkey@racsa.co.cr> * * 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 <stdbool.h> #include <semaphore.h> #include <sched.h> #include <errno.h> #include <nuttx/arch.h> #include "os_internal.h" #include "sem_internal.h" /**************************************************************************** * Pre-processor Definitions ****************************************************************************/ /**************************************************************************** * Private Type Declarations ****************************************************************************/ /**************************************************************************** * Global Variables ****************************************************************************/ /**************************************************************************** * Private Variables ****************************************************************************/ /**************************************************************************** * Private Functions ****************************************************************************/ /**************************************************************************** * Public Functions ****************************************************************************/ /**************************************************************************** * Function: sem_trywait * * Description: * This function locks the specified semaphore only if the * semaphore is currently not locked. Otherwise, it locks * the semaphore. In either case, the call returns without * blocking. * * Parameters: * sem - the semaphore descriptor * * Return Value: * 0 (OK) or -1 (ERROR) if unsuccessful * If this function returns -1 (ERROR), then the cause * of the failure will be reported in "errno" as: * - EINVAL: Invalid attempt to get the semaphore * - EAGAIN: The semaphore is not available. * * Assumptions: * ****************************************************************************/ int sem_trywait(FAR sem_t *sem) { FAR _TCB *rtcb = (FAR _TCB*)g_readytorun.head; irqstate_t saved_state; int ret = ERROR; /* This API should not be called from interrupt handlers */ DEBUGASSERT(up_interrupt_context() == false) /* Assume any errors reported are due to invalid arguments. */ *get_errno_ptr() = EINVAL; if (sem) { /* The following operations must be performed with interrupts * disabled because sem_post() may be called from an interrupt * handler. */ saved_state = irqsave(); /* Any further errors could only be occurred because the semaphore * is not available. */ *get_errno_ptr() = EAGAIN; /* If the semaphore is available, give it to the requesting task */ if (sem->semcount > 0) { /* It is, let the task take the semaphore */ sem->semcount--; rtcb->waitsem = NULL; ret = OK; } /* Interrupts may now be enabled. */ irqrestore(saved_state); } return ret; }