c9bdadd541
This moves all the public POSIX semaphore functions into libc and with this most of the user-space logic is also moved; namely cancel point and errno handling. This also removes the need for the _SEM_XX macros used to differentiate which API is used per user-/kernel mode. Such macros are henceforth unnecessary.
107 lines
3.4 KiB
C
107 lines
3.4 KiB
C
/****************************************************************************
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* sched/semaphore/sem_setprotocol.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 <assert.h>
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#include <errno.h>
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#include "semaphore/semaphore.h"
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#ifdef CONFIG_PRIORITY_INHERITANCE
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: nxsem_set_protocol
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*
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* Description:
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* Set semaphore protocol attribute.
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*
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* One particularly important use of this function is when a semaphore
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* is used for inter-task communication like:
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*
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* TASK A TASK B
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* nxsem_init(sem, 0, 0);
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* nxsem_wait(sem);
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* nxsem_post(sem);
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* Awakens as holder
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*
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* In this case priority inheritance can interfere with the operation of
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* the semaphore. The problem is that when TASK A is restarted it is a
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* holder of the semaphore. However, it never calls nxsem_post(sem) so it
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* becomes *permanently* a holder of the semaphore and may have its
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* priority boosted when any other task tries to acquire the semaphore.
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*
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* The fix is to call nxsem_set_protocol(SEM_PRIO_NONE) immediately after
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* the sem_init() call so that there will be no priority inheritance
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* operations on this semaphore.
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*
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* Input Parameters:
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* sem - A pointer to the semaphore whose attributes are to be
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* modified
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* protocol - The new protocol to use
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*
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* Returned Value:
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* This is an internal OS interface and should not be used by applications.
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* It 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_set_protocol(FAR sem_t *sem, int protocol)
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{
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DEBUGASSERT(sem != NULL);
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switch (protocol & SEM_PRIO_MASK)
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{
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case SEM_PRIO_NONE:
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/* Remove any current holders */
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nxsem_destroyholder(sem);
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break;
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case SEM_PRIO_INHERIT:
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break;
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case SEM_PRIO_PROTECT:
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/* Not yet supported */
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return -ENOTSUP;
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default:
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return -EINVAL;
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}
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sem->flags = protocol;
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return OK;
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}
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#endif /* CONFIG_PRIORITY_INHERITANCE */
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