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bb85ad849e
The load/compare and RMW to wait_count need protection. Using atomic operations should resolve both issues. NOTE: The assumption that the user will call pthread_cond_signal / pthread_cond_broadcast with the mutex given to pthread_cond_wait held is simply not true. It MAY hold it, but it is not forced. Thus, using the user space lock for protecting the wait counter as well is not valid! The pthread_cond_signal() or pthread_cond_broadcast() functions may be called by a thread whether or not it currently owns the mutex that threads calling pthread_cond_wait() or pthread_cond_timedwait() have associated with the condition variable during their waits; however, if predictable scheduling behaviour is required, then that mutex is locked by the thread calling pthread_cond_signal() or pthread_cond_broadcast(). [1] https://pubs.opengroup.org/onlinepubs/7908799/xsh/pthread_cond_signal.html
125 lines
3.3 KiB
C
125 lines
3.3 KiB
C
/****************************************************************************
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* sched/pthread/pthread_condwait.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 <unistd.h>
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#include <pthread.h>
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#include <sched.h>
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#include <errno.h>
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#include <debug.h>
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#include <nuttx/atomic.h>
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#include <nuttx/cancelpt.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: int pthread_cond_wait
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*
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* Description:
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* A thread can wait for a condition variable to be signalled or broadcast.
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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_wait(FAR pthread_cond_t *cond, FAR pthread_mutex_t *mutex)
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{
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int status;
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int ret;
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sinfo("cond=%p mutex=%p\n", cond, mutex);
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/* pthread_cond_wait() is a cancellation point */
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enter_cancellation_point();
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/* Make sure that non-NULL references were provided. */
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if (cond == NULL || mutex == NULL)
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{
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ret = EINVAL;
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}
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/* Make sure that the caller holds the mutex */
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else if (!mutex_is_hold(&mutex->mutex))
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{
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ret = EPERM;
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}
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else
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{
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unsigned int nlocks;
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/* Give up the mutex */
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sinfo("Give up mutex / take cond\n");
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atomic_fetch_add(COND_WAIT_COUNT(cond), 1);
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ret = pthread_mutex_breaklock(mutex, &nlocks);
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status = -nxsem_wait_uninterruptible(&cond->sem);
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if (ret == OK)
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{
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/* Report the first failure that occurs */
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ret = status;
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}
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/* Reacquire the mutex.
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*
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* When cancellation points are enabled, we need to hold the mutex
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* when the pthread is canceled and cleanup handlers, if any, are
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* entered.
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*/
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sinfo("Reacquire mutex...\n");
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status = pthread_mutex_restorelock(mutex, nlocks);
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if (ret == OK)
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{
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/* Report the first failure that occurs */
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ret = status;
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}
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}
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leave_cancellation_point();
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sinfo("Returning %d\n", ret);
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return ret;
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}
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