21c97b16cf
What was I thinking? I missed that litle minus sign and the possibility that the errno might be some positive non-zero value.
This reverts commit 43880878e4.
270 lines
8.7 KiB
C
270 lines
8.7 KiB
C
/****************************************************************************
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* sched/semaphore/sem_wait.c
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*
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* Copyright (C) 2007-2013, 2016 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <stdbool.h>
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#include <semaphore.h>
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#include <errno.h>
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#include <assert.h>
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#include <nuttx/irq.h>
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#include <nuttx/arch.h>
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#include <nuttx/cancelpt.h>
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#include "sched/sched.h"
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#include "semaphore/semaphore.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: nxsem_wait
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*
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* Description:
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* This function attempts to lock the semaphore referenced by 'sem'. If
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* the semaphore value is (<=) zero, then the calling task will not return
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* until it successfully acquires the lock.
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*
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* This is an internal OS interface. It is functionally equivalent to
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* sem_wait except that:
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*
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* - It is not a cancellaction point, and
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* - It does not modify the errno value.
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*
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* Parameters:
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* sem - Semaphore descriptor.
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*
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* Return Value:
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* This is an internal OS interface and should not be used by applications.
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* It follows the NuttX internal error return policy: Zero (OK) is
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* returned on success. A negated errno value is returned on failure.
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* Possible returned errors:
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*
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* - EINVAL: Invalid attempt to get the semaphore
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* - EINTR: The wait was interrupted by the receipt of a signal.
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*
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****************************************************************************/
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int nxsem_wait(FAR sem_t *sem)
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{
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FAR struct tcb_s *rtcb = this_task();
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irqstate_t flags;
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int ret = -EINVAL;
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/* This API should not be called from interrupt handlers */
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DEBUGASSERT(sem != NULL && up_interrupt_context() == false);
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/* The following operations must be performed with interrupts
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* disabled because nxsem_post() may be called from an interrupt
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* handler.
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*/
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flags = enter_critical_section();
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/* Make sure we were supplied with a valid semaphore. */
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if (sem != NULL)
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{
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/* Check if the lock is available */
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if (sem->semcount > 0)
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{
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/* It is, let the task take the semaphore. */
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sem->semcount--;
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nxsem_addholder(sem);
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rtcb->waitsem = NULL;
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ret = OK;
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}
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/* The semaphore is NOT available, We will have to block the
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* current thread of execution.
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*/
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else
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{
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int saved_errno;
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/* First, verify that the task is not already waiting on a
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* semaphore
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*/
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ASSERT(rtcb->waitsem == NULL);
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/* Handle the POSIX semaphore (but don't set the owner yet) */
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sem->semcount--;
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/* Save the waited on semaphore in the TCB */
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rtcb->waitsem = sem;
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/* If priority inheritance is enabled, then check the priority of
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* the holder of the semaphore.
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*/
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#ifdef CONFIG_PRIORITY_INHERITANCE
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/* Disable context switching. The following operations must be
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* atomic with regard to the scheduler.
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*/
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sched_lock();
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/* Boost the priority of any threads holding a count on the
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* semaphore.
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*/
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nxsem_boostpriority(sem);
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#endif
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/* Set the errno value to zero (preserving the original errno)
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* value). We reuse the per-thread errno to pass information
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* between sem_waitirq() and this functions.
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*/
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saved_errno = rtcb->pterrno;
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rtcb->pterrno = OK;
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/* Add the TCB to the prioritized semaphore wait queue */
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up_block_task(rtcb, TSTATE_WAIT_SEM);
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/* When we resume at this point, either (1) the semaphore has been
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* assigned to this thread of execution, or (2) the semaphore wait
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* has been interrupted by a signal or a timeout. We can detect these
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* latter cases be examining the per-thread errno value.
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*
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* In the event that the semaphore wait was interrupted by a signal or
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* a timeout, certain semaphore clean-up operations have already been
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* performed (see sem_waitirq.c). Specifically:
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*
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* - nxsem_canceled() was called to restore the priority of all
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* threads that hold a reference to the semaphore,
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* - The semaphore count was decremented, and
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* - tcb->waitsem was nullifed.
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*
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* It is necesaary to do these things in sem_waitirq.c because a long
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* time may elapse between the time that the signal was issued and
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* this thread is awakened and this leaves a door open to several
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* race conditions.
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*/
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/* Check if an error occurred while we were sleeping. Expected
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* errors include EINTR meaning that we were awakened by a signal
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* or ETIMEDOUT meaning that the timer expired for the case of
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* sem_timedwait().
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*
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* If we were not awakened by a signal or a timeout, then
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* nxsem_addholder() was called by logic in sem_wait() fore this
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* thread was restarted.
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*/
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ret = rtcb->pterrno != OK ? -rtcb->pterrno : OK;
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rtcb->pterrno = saved_errno;
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#ifdef CONFIG_PRIORITY_INHERITANCE
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sched_unlock();
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#endif
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}
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}
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leave_critical_section(flags);
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return ret;
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}
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/****************************************************************************
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* Name: sem_wait
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*
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* Description:
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* This function attempts to lock the semaphore referenced by 'sem'. If
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* the semaphore value is (<=) zero, then the calling task will not return
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* until it successfully acquires the lock.
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*
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* Parameters:
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* sem - Semaphore descriptor.
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*
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* Return Value:
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* This function is a standard, POSIX application interface. It returns
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* zero (OK) if successful. Otherwise, -1 (ERROR) is returned and
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* the errno value is set appropriately. Possible errno values include:
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*
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* - EINVAL: Invalid attempt to get the semaphore
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* - EINTR: The wait was interrupted by the receipt of a signal.
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*
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****************************************************************************/
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int sem_wait(FAR sem_t *sem)
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{
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int errcode;
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int ret;
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/* sem_wait() is a cancellation point */
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if (enter_cancellation_point())
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{
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#ifdef CONFIG_CANCELLATION_POINTS
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/* If there is a pending cancellation, then do not perform
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* the wait. Exit now with ECANCELED.
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*/
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errcode = ECANCELED;
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goto errout_with_cancelpt;
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#endif
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}
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/* Let nxsem_wait() do the real work */
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ret = nxsem_wait(sem);
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if (ret < 0)
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{
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errcode = -ret;
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goto errout_with_cancelpt;
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}
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leave_cancellation_point();
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return OK;
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errout_with_cancelpt:
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set_errno(errcode);
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leave_cancellation_point();
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return ERROR;
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}
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