b6f2729730
This puts the mutex support fully inside nxsem, allowing locking the mutex and setting the holder with single atomic operation. This enables fast mutex locking from userspace, avoiding taking critical_sections, which may be heavy in SMP and cleanup of nxmutex library in the future. Signed-off-by: Jukka Laitinen <jukka.laitinen@tii.ae>
139 lines
4.4 KiB
C
139 lines
4.4 KiB
C
/****************************************************************************
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* libs/libc/semaphore/sem_init.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 <sys/types.h>
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#include <assert.h>
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#include <limits.h>
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#include <errno.h>
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#include <nuttx/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_init
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*
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* Description:
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* This function initializes the UNNAMED semaphore sem. Following a
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* successful call to nxsem_init(), the semaphore may be used in subsequent
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* calls to nxsem_wait(), nxsem_post(), and nxsem_trywait(). The semaphore
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* remains usable until it is destroyed.
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*
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* Only sem itself may be used for performing synchronization. The result
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* of referring to copies of sem in calls to nxsem_wait(), nxsem_trywait(),
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* nxsem_post(), and nxsem_destroy() is undefined.
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*
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* Input Parameters:
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* sem - Semaphore to be initialized
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* pshared - Process sharing (not used)
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* value - Semaphore initialization value
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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_init(FAR sem_t *sem, int pshared, uint32_t value)
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{
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UNUSED(pshared);
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DEBUGASSERT(sem != NULL);
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/* Initialize the semaphore count or mutex holder */
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sem->val.semcount = (int32_t)value;
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/* Initialize semaphore wait list */
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dq_init(&sem->waitlist);
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/* Initialize to support priority inheritance */
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sem->flags = 0;
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#ifdef CONFIG_PRIORITY_INHERITANCE
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# if CONFIG_SEM_PREALLOCHOLDERS > 0
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sem->hhead = NULL;
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# else
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INITIALIZE_SEMHOLDER(&sem->holder);
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# endif
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#endif
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return OK;
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}
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/****************************************************************************
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* Name: sem_init
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*
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* Description:
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* This function initializes the UNNAMED semaphore sem. Following a
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* successful call to sem_init(), the semaphore may be used in subsequent
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* calls to sem_wait(), sem_post(), and sem_trywait(). The semaphore
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* remains usable until it is destroyed.
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*
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* Only sem itself may be used for performing synchronization. The result
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* of referring to copies of sem in calls to sem_wait(), sem_trywait(),
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* sem_post(), and sem_destroy() is undefined.
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*
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* Input Parameters:
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* sem - Semaphore to be initialized
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* pshared - Process sharing (not used)
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* value - Semaphore initialization value
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*
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* Returned Value:
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* This returns zero (OK) if successful. Otherwise, -1 (ERROR) is
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* returned and the errno value is set appropriately.
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*
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****************************************************************************/
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int sem_init(FAR sem_t *sem, int pshared, unsigned int value)
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{
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int ret;
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/* Verify that a semaphore was provided and the count is within the valid
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* range.
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*/
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if (sem == NULL || value > SEM_VALUE_MAX)
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{
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set_errno(EINVAL);
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return ERROR;
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}
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ret = nxsem_init(sem, pshared, value);
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if (ret < 0)
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{
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set_errno(-ret);
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ret = ERROR;
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}
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return ret;
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}
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