/**************************************************************************** * sched/semaphore/sem_trywait.c * * Copyright (C) 2007-2009, 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_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. * * Input Parameters: * sem - the 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. * Possible returned errors: * * EINVAL - Invalid attempt to get the semaphore * EAGAIN - The semaphore is not available. * * Assumptions: * ****************************************************************************/ int nxsem_trywait(FAR sem_t *sem) { FAR struct tcb_s *rtcb = this_task(); irqstate_t flags; int ret; /* This API should not be called from interrupt handlers */ DEBUGASSERT(sem != NULL && up_interrupt_context() == false); 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(); /* 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; } else { /* Semaphore is not available */ ret = -EAGAIN; } /* Interrupts may now be enabled. */ leave_critical_section(flags); } else { ret = -EINVAL; } return ret; } /**************************************************************************** * Name: 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. * * Input Parameters: * sem - the semaphore descriptor * * Returned Value: * Zero (OK) on success or -1 (ERROR) if unsuccessful. If this function * returns -1(ERROR), then the cause of the failure will be reported in * errno variable as: * * EINVAL - Invalid attempt to get the semaphore * EAGAIN - The semaphore is not available. * ****************************************************************************/ int sem_trywait(FAR sem_t *sem) { int ret; /* Let nxsem_trywait do the real work */ ret = nxsem_trywait(sem); if (ret < 0) { set_errno(-ret); ret = ERROR; } return ret; }