126 lines
4.4 KiB
C
126 lines
4.4 KiB
C
/****************************************************************************
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* sched/semaphore/sem_reset.c
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*
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* Copyright (C) 2016-2017 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 <semaphore.h>
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#include <sched.h>
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#include <assert.h>
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#include <nuttx/irq.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_reset
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*
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* Description:
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* Reset a semaphore count to a specific value. This is similar to part
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* of the operation of nxsem_init(). But nxsem_reset() may need to wake up
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* tasks waiting on a count. This kind of operation is sometimes required
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* within the OS (only) for certain error handling conditions.
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*
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* Parameters:
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* sem - Semaphore descriptor to be reset
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* count - The requested semaphore count
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*
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* Returned Value:
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* This is an internal OS interface, not available to applications, and
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* hence 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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*
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****************************************************************************/
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int nxsem_reset(FAR sem_t *sem, int16_t count)
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{
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irqstate_t flags;
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DEBUGASSERT(sem != NULL && count >= 0);
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/* Don't allow any context switches that may result from the following
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* nxsem_post() operations.
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*/
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sched_lock();
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/* Prevent any access to the semaphore by interrupt handlers while we are
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* performing this operation.
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*/
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flags = enter_critical_section();
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/* A negative count indicates that the negated number of threads are
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* waiting to take a count from the semaphore. Loop here, handing
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* out counts to any waiting threads.
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*/
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while (sem->semcount < 0 && count > 0)
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{
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/* Give out one counting, waking up one of the waiting threads
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* and, perhaps, kicking off a lot of priority inheritance
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* logic (REVISIT).
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*/
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DEBUGVERIFY(nxsem_post(sem));
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count--;
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}
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/* We exit the above loop with either (1) no threads waiting for the
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* (i.e., with sem->semcount >= 0). In this case, 'count' holds the
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* the new value of the semaphore count. OR (2) with threads still
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* waiting but all of the semaphore counts exhausted: The current
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* value of sem->semcount is already correct in this case.
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*/
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if (sem->semcount >= 0)
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{
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sem->semcount = count;
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}
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/* Allow any pending context switches to occur now */
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leave_critical_section(flags);
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sched_unlock();
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return OK;
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}
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