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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>
137 lines
3.4 KiB
C
137 lines
3.4 KiB
C
/****************************************************************************
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* sched/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 <stdbool.h>
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#include <sched.h>
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#include <assert.h>
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#include <errno.h>
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#include <nuttx/init.h>
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#include <nuttx/irq.h>
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#include <nuttx/arch.h>
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#include "sched/sched.h"
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#include "semaphore/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_trywait_slow
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*
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* Description:
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* This function locks the specified semaphore in slow mode.
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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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*
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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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* Assumptions:
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*
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****************************************************************************/
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int nxsem_trywait_slow(FAR sem_t *sem)
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{
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irqstate_t flags;
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int ret = -EAGAIN;
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bool mutex = NXSEM_IS_MUTEX(sem);
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FAR atomic_t *val = mutex ? NXSEM_MHOLDER(sem) : NXSEM_COUNT(sem);
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int32_t old;
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int32_t new;
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/* The following operations must be performed with interrupts disabled
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* because sem_post() may be called from an interrupt handler.
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*/
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flags = enter_critical_section();
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/* If the semaphore is available, give it to the requesting task */
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if (mutex)
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{
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new = nxsched_gettid();
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}
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old = atomic_read(val);
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do
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{
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if (mutex)
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{
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if (NXSEM_MACQUIRED(old))
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{
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goto out;
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}
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}
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else
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{
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if (old <= 0)
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{
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goto out;
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}
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new = old - 1;
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}
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}
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while (!atomic_try_cmpxchg_acquire(val, &old, new));
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/* It is, let the task take the semaphore */
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ret = nxsem_protect_wait(sem);
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if (ret < 0)
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{
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if (mutex)
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{
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atomic_set(NXSEM_MHOLDER(sem), NXSEM_NO_MHOLDER);
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}
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else
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{
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atomic_fetch_add(NXSEM_COUNT(sem), 1);
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}
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leave_critical_section(flags);
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goto out;
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}
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if (!mutex)
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{
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nxsem_add_holder(sem);
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}
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out:
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/* Interrupts may now be enabled. */
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leave_critical_section(flags);
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return ret;
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}
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