273 lines
8.8 KiB
C
273 lines
8.8 KiB
C
/****************************************************************************
|
|
* sched/semaphore/sem_wait.c
|
|
*
|
|
* Copyright (C) 2007-2013, 2016 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 <errno.h>
|
|
#include <assert.h>
|
|
|
|
#include <nuttx/irq.h>
|
|
#include <nuttx/arch.h>
|
|
#include <nuttx/cancelpt.h>
|
|
|
|
#include "sched/sched.h"
|
|
#include "semaphore/semaphore.h"
|
|
|
|
/****************************************************************************
|
|
* Public Functions
|
|
****************************************************************************/
|
|
|
|
/****************************************************************************
|
|
* Name: nxsem_wait
|
|
*
|
|
* Description:
|
|
* This function attempts to lock the semaphore referenced by 'sem'. If
|
|
* the semaphore value is (<=) zero, then the calling task will not return
|
|
* until it successfully acquires the lock.
|
|
*
|
|
* This is an internal OS interface. It is functionally equivalent to
|
|
* sem_wait except that:
|
|
*
|
|
* - It is not a cancellation point, and
|
|
* - It does not modify the errno value.
|
|
*
|
|
* Input Parameters:
|
|
* sem - 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
|
|
* - EINTR: The wait was interrupted by the receipt of a signal.
|
|
*
|
|
****************************************************************************/
|
|
|
|
int nxsem_wait(FAR sem_t *sem)
|
|
{
|
|
FAR struct tcb_s *rtcb = this_task();
|
|
irqstate_t flags;
|
|
int ret = -EINVAL;
|
|
|
|
/* This API should not be called from interrupt handlers */
|
|
|
|
DEBUGASSERT(sem != NULL && up_interrupt_context() == false);
|
|
|
|
/* The following operations must be performed with interrupts
|
|
* disabled because nxsem_post() may be called from an interrupt
|
|
* handler.
|
|
*/
|
|
|
|
flags = enter_critical_section();
|
|
|
|
/* Make sure we were supplied with a valid semaphore. */
|
|
|
|
if (sem != NULL)
|
|
{
|
|
/* Check if the lock is available */
|
|
|
|
if (sem->semcount > 0)
|
|
{
|
|
/* It is, let the task take the semaphore. */
|
|
|
|
sem->semcount--;
|
|
nxsem_addholder(sem);
|
|
rtcb->waitsem = NULL;
|
|
ret = OK;
|
|
}
|
|
|
|
/* The semaphore is NOT available, We will have to block the
|
|
* current thread of execution.
|
|
*/
|
|
|
|
else
|
|
{
|
|
int saved_errno;
|
|
|
|
/* First, verify that the task is not already waiting on a
|
|
* semaphore
|
|
*/
|
|
|
|
DEBUGASSERT(rtcb->waitsem == NULL);
|
|
|
|
/* Handle the POSIX semaphore (but don't set the owner yet) */
|
|
|
|
sem->semcount--;
|
|
|
|
/* Save the waited on semaphore in the TCB */
|
|
|
|
rtcb->waitsem = sem;
|
|
|
|
/* If priority inheritance is enabled, then check the priority of
|
|
* the holder of the semaphore.
|
|
*/
|
|
|
|
#ifdef CONFIG_PRIORITY_INHERITANCE
|
|
/* Disable context switching. The following operations must be
|
|
* atomic with regard to the scheduler.
|
|
*/
|
|
|
|
sched_lock();
|
|
|
|
/* Boost the priority of any threads holding a count on the
|
|
* semaphore.
|
|
*/
|
|
|
|
nxsem_boostpriority(sem);
|
|
#endif
|
|
/* Set the errno value to zero (preserving the original errno)
|
|
* value). We reuse the per-thread errno to pass information
|
|
* between sem_waitirq() and this functions.
|
|
*/
|
|
|
|
saved_errno = rtcb->pterrno;
|
|
rtcb->pterrno = OK;
|
|
|
|
/* Add the TCB to the prioritized semaphore wait queue, after
|
|
* checking this is not the idle task - descheduling that
|
|
* isn't going to end well.
|
|
*/
|
|
|
|
DEBUGASSERT(NULL != rtcb->flink);
|
|
up_block_task(rtcb, TSTATE_WAIT_SEM);
|
|
|
|
/* When we resume at this point, either (1) the semaphore has been
|
|
* assigned to this thread of execution, or (2) the semaphore wait
|
|
* has been interrupted by a signal or a timeout. We can detect these
|
|
* latter cases be examining the per-thread errno value.
|
|
*
|
|
* In the event that the semaphore wait was interrupted by a signal or
|
|
* a timeout, certain semaphore clean-up operations have already been
|
|
* performed (see sem_waitirq.c). Specifically:
|
|
*
|
|
* - nxsem_canceled() was called to restore the priority of all
|
|
* threads that hold a reference to the semaphore,
|
|
* - The semaphore count was decremented, and
|
|
* - tcb->waitsem was nullifed.
|
|
*
|
|
* It is necesaary to do these things in sem_waitirq.c because a long
|
|
* time may elapse between the time that the signal was issued and
|
|
* this thread is awakened and this leaves a door open to several
|
|
* race conditions.
|
|
*/
|
|
|
|
/* Check if an error occurred while we were sleeping. Expected
|
|
* errors include EINTR meaning that we were awakened by a signal
|
|
* or ETIMEDOUT meaning that the timer expired for the case of
|
|
* sem_timedwait().
|
|
*
|
|
* If we were not awakened by a signal or a timeout, then
|
|
* nxsem_addholder() was called by logic in sem_wait() fore this
|
|
* thread was restarted.
|
|
*/
|
|
|
|
ret = rtcb->pterrno != OK ? -rtcb->pterrno : OK;
|
|
rtcb->pterrno = saved_errno;
|
|
|
|
#ifdef CONFIG_PRIORITY_INHERITANCE
|
|
sched_unlock();
|
|
#endif
|
|
}
|
|
}
|
|
|
|
leave_critical_section(flags);
|
|
return ret;
|
|
}
|
|
|
|
/****************************************************************************
|
|
* Name: sem_wait
|
|
*
|
|
* Description:
|
|
* This function attempts to lock the semaphore referenced by 'sem'. If
|
|
* the semaphore value is (<=) zero, then the calling task will not return
|
|
* until it successfully acquires the lock.
|
|
*
|
|
* Input Parameters:
|
|
* sem - Semaphore descriptor.
|
|
*
|
|
* Returned Value:
|
|
* This function is a standard, POSIX application interface. It returns
|
|
* zero (OK) if successful. Otherwise, -1 (ERROR) is returned and
|
|
* the errno value is set appropriately. Possible errno values include:
|
|
*
|
|
* - EINVAL: Invalid attempt to get the semaphore
|
|
* - EINTR: The wait was interrupted by the receipt of a signal.
|
|
*
|
|
****************************************************************************/
|
|
|
|
int sem_wait(FAR sem_t *sem)
|
|
{
|
|
int errcode;
|
|
int ret;
|
|
|
|
/* sem_wait() is a cancellation point */
|
|
|
|
if (enter_cancellation_point())
|
|
{
|
|
#ifdef CONFIG_CANCELLATION_POINTS
|
|
/* If there is a pending cancellation, then do not perform
|
|
* the wait. Exit now with ECANCELED.
|
|
*/
|
|
|
|
errcode = ECANCELED;
|
|
goto errout_with_cancelpt;
|
|
#endif
|
|
}
|
|
|
|
/* Let nxsem_wait() do the real work */
|
|
|
|
ret = nxsem_wait(sem);
|
|
if (ret < 0)
|
|
{
|
|
errcode = -ret;
|
|
goto errout_with_cancelpt;
|
|
}
|
|
|
|
leave_cancellation_point();
|
|
return OK;
|
|
|
|
errout_with_cancelpt:
|
|
set_errno(errcode);
|
|
leave_cancellation_point();
|
|
return ERROR;
|
|
}
|