diff options
Diffstat (limited to 'nuttx/sched/sem_trywait.c')
-rw-r--r-- | nuttx/sched/sem_trywait.c | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/nuttx/sched/sem_trywait.c b/nuttx/sched/sem_trywait.c new file mode 100644 index 000000000..cbd8dae69 --- /dev/null +++ b/nuttx/sched/sem_trywait.c @@ -0,0 +1,142 @@ +/**************************************************************************** + * sched/sem_trywait.c + * + * Copyright (C) 2007-2009 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 <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 + ****************************************************************************/ + +/**************************************************************************** + * 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. + * + * 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. */ + + set_errno(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. + */ + + set_errno(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; +} |