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19a8e2403f
This avoids unnecessary syscalls in memory protected builds, when mutex lock/unlock can be done with only atomic counter access Signed-off-by: Jukka Laitinen <jukka.laitinen@tii.ae>
139 lines
4.2 KiB
C
139 lines
4.2 KiB
C
/****************************************************************************
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* libs/libc/semaphore/sem_trywait.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 <assert.h>
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#include <sched.h>
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#include <nuttx/init.h>
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#include <nuttx/semaphore.h>
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#include <nuttx/atomic.h>
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#include <nuttx/irq.h>
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: sem_trywait
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*
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* Description:
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* This function locks the specified semaphore only if the semaphore is
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* currently not locked. In either case, the call returns without
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* blocking.
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*
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* Input Parameters:
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* sem - the semaphore descriptor
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*
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* Returned Value:
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* Zero (OK) on success or -1 (ERROR) if unsuccessful. If this function
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* returns -1(ERROR), then the cause of the failure will be reported in
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* errno variable as:
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*
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* EINVAL - Invalid attempt to get the semaphore
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* EAGAIN - The semaphore is not available.
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*
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****************************************************************************/
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int sem_trywait(FAR sem_t *sem)
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{
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int ret;
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if (sem == NULL)
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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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/* Let nxsem_trywait do the real work */
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ret = nxsem_trywait(sem);
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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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/****************************************************************************
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* Name: nxsem_trywait
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*
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* Description:
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* This function locks the specified semaphore only if the semaphore is
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* currently not locked. In either case, the call returns without
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* blocking.
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*
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* Input Parameters:
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* sem - the semaphore descriptor
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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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* Possible returned errors:
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*
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* - EINVAL - Invalid attempt to get the semaphore
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* - EAGAIN - The semaphore is not available.
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*
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****************************************************************************/
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int nxsem_trywait(FAR sem_t *sem)
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{
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DEBUGASSERT(sem != NULL);
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/* This API should not be called from the idleloop or interrupt */
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#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
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DEBUGASSERT(!OSINIT_IDLELOOP() || !sched_idletask() ||
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up_interrupt_context());
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#endif
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/* We don't do atomic fast path in case of LIBC_ARCH_ATOMIC because that
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* uses spinlocks, which can't be called from userspace. Also in the kernel
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* taking the slow path directly is faster than locking first in here
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*/
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#ifndef CONFIG_LIBC_ARCH_ATOMIC
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if ((sem->flags & SEM_TYPE_MUTEX)
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#if defined(CONFIG_PRIORITY_PROTECT) || defined(CONFIG_PRIORITY_INHERITANCE)
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&& (sem->flags & SEM_PRIO_MASK) == SEM_PRIO_NONE
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#endif
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)
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{
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int32_t old = 1;
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return atomic_try_cmpxchg_acquire(NXSEM_COUNT(sem), &old, 0) ?
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OK : -EAGAIN;
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}
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#endif
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return nxsem_trywait_slow(sem);
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}
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