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>
111 lines
4 KiB
C
111 lines
4 KiB
C
/****************************************************************************
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* libs/libc/semaphore/sem_getvalue.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 <errno.h>
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#include <nuttx/semaphore.h>
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#include <nuttx/atomic.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_get_value
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*
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* Description:
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* This function updates the location referenced by 'sval' argument to
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* have the value of the semaphore referenced by 'sem' without effecting
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* the state of the semaphore. The updated value represents the actual
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* semaphore value that occurred at some unspecified time during the call,
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* but may not reflect the actual value of the semaphore when it is
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* returned to the calling task.
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*
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* If 'sem' is locked, then the object to which 'sval' points shall either
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* be zero or a negative number whose absolute value represents the number
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* of tasks waiting for the semaphore.
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*
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* Input Parameters:
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* sem - Semaphore descriptor
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* sval - Buffer by which the value is returned
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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_get_value(FAR sem_t *sem, FAR int *sval)
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{
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if (sem != NULL && sval != NULL && !NXSEM_IS_MUTEX(sem))
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{
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*sval = atomic_read(NXSEM_COUNT(sem));
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return OK;
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}
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return -EINVAL;
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}
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/****************************************************************************
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* Name: sem_getvalue
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*
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* Description:
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* This function updates the location referenced by 'sval' argument to
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* have the value of the semaphore referenced by 'sem' without effecting
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* the state of the semaphore. The updated value represents the actual
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* semaphore value that occurred at some unspecified time during the call,
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* but may not reflect the actual value of the semaphore when it is
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* returned to the calling task.
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*
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* If 'sem' is locked, then the object to which 'sval' points shall either
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* be zero or a negative number whose absolute value represents the number
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* of tasks waiting for the semaphore.
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*
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* Input Parameters:
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* sem - Semaphore descriptor
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* sval - Buffer by which the value is returned
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*
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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_getvalue(FAR sem_t *sem, FAR int *sval)
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{
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int ret;
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ret = nxsem_get_value(sem, sval);
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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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