110 lines
3.6 KiB
C
110 lines
3.6 KiB
C
/****************************************************************************
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* sched/semaphore/sem_reset.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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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 <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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* Input 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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