104 lines
3.1 KiB
C
104 lines
3.1 KiB
C
/****************************************************************************
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* sched/pthread/pthread_condsignal.c
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*
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* SPDX-License-Identifier: Apache-2.0
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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 <pthread.h>
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#include <errno.h>
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#include <debug.h>
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#include "pthread/pthread.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: pthread_cond_signal
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*
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* Description:
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* A thread can signal on a condition variable.
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*
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* Input Parameters:
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* None
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*
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* Returned Value:
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* None
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*
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* Assumptions:
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*
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****************************************************************************/
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int pthread_cond_signal(FAR pthread_cond_t *cond)
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{
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int ret = OK;
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int sval;
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sinfo("cond=%p\n", cond);
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if (!cond)
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{
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ret = EINVAL;
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}
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else
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{
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/* Get the current value of the semaphore */
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if (nxsem_get_value(&cond->sem, &sval) != OK)
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{
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ret = EINVAL;
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}
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/* If the value is less than zero (meaning that one or more
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* thread is waiting), then post the condition semaphore.
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* Only the highest priority waiting thread will get to execute
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*/
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else
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{
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/* One of my objectives in this design was to make
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* pthread_cond_signal() usable from interrupt handlers. However,
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* from interrupt handlers, you cannot take the associated mutex
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* before signaling the condition. As a result, I think that
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* there could be a race condition with the following logic which
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* assumes that the if sval < 0 then the thread is waiting.
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* Without the mutex, there is no atomic, protected operation that
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* will guarantee this to be so.
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*/
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sinfo("sval=%d\n", sval);
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if (sval < 0)
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{
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sinfo("Signalling...\n");
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ret = -nxsem_post(&cond->sem);
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}
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}
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}
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sinfo("Returning %d\n", ret);
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return ret;
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}
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