353 lines
8.8 KiB
C
353 lines
8.8 KiB
C
/****************************************************************************
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* sched/semaphore/sem_rw.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/rwsem.h>
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#include <nuttx/sched.h>
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#include <assert.h>
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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static inline void up_wait(FAR rw_semaphore_t *rwsem)
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{
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int i;
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for (i = 0; i < rwsem->waiter; i++)
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{
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/* If there are some waiter for unlock, then post the lock wait queue.
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*/
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nxsem_post(&rwsem->waiting);
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}
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}
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: down_read_trylock
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*
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* Description:
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* Acquire a read lock on a read-write-lock object.
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*
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* Input Parameters:
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* rwsem - Pointer to the read-write-lock descriptor.
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*
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* Returned Value:
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* Return 1 if successful, 0 if failed
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*
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****************************************************************************/
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int down_read_trylock(FAR rw_semaphore_t *rwsem)
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{
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nxmutex_lock(&rwsem->protected);
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/* if the write lock is already held by oneself and since the write lock
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* can be recursively held, so, this operation can be converted to a write
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* lock to avoid deadlock.
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*/
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if (rwsem->holder == _SCHED_GETTID())
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{
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rwsem->writer++;
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goto out;
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}
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if (rwsem->writer > 0)
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{
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nxmutex_unlock(&rwsem->protected);
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return 0;
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}
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/* In a scenario where there is no write lock, we just need to make the
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* read base +1.
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*/
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rwsem->reader++;
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out:
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nxmutex_unlock(&rwsem->protected);
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return 1;
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}
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/****************************************************************************
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* Name: down_read
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*
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* Description:
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* Acquire a read lock on a read-write-lock object.
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*
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* Input Parameters:
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* rwsem - Pointer to the read-write-lock descriptor.
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*
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****************************************************************************/
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void down_read(FAR rw_semaphore_t *rwsem)
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{
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/* we have to check if there is a write-lock scenario, if there is then we
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* block and wait for the write-lock to be unlocked.
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*/
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nxmutex_lock(&rwsem->protected);
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/* if the write lock is already held by oneself and since the write lock
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* can be recursively held, so, this operation can be converted to a write
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* lock to avoid deadlock.
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*/
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if (rwsem->holder == _SCHED_GETTID())
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{
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rwsem->writer++;
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goto out;
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}
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while (rwsem->writer > 0)
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{
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rwsem->waiter++;
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nxmutex_unlock(&rwsem->protected);
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nxsem_wait(&rwsem->waiting);
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nxmutex_lock(&rwsem->protected);
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rwsem->waiter--;
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}
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/* In a scenario where there is no write lock, we just need to make the
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* read base +1.
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*/
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rwsem->reader++;
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out:
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nxmutex_unlock(&rwsem->protected);
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}
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/****************************************************************************
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* Name: up_read
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*
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* Description:
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* Unlock a read lock on a read-write-lock object.
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*
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* Input Parameters:
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* rwsem - Pointer to the read-write-lock descriptor.
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*
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****************************************************************************/
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void up_read(FAR rw_semaphore_t *rwsem)
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{
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nxmutex_lock(&rwsem->protected);
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/* when releasing a read lock and holder is oneself, the read lock is a
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* write lock that has been converted, so it should be released according
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* to the procedures for releasing a write lock.
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*/
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if (rwsem->holder == _SCHED_GETTID())
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{
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if (--rwsem->writer <= 0)
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{
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rwsem->holder = RWSEM_NO_HOLDER;
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}
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goto out;
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}
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DEBUGASSERT(rwsem->reader > 0);
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rwsem->reader--;
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if (rwsem->waiter > 0)
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{
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up_wait(rwsem);
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}
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out:
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nxmutex_unlock(&rwsem->protected);
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}
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/****************************************************************************
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* Name: down_write_trylock
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*
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* Description:
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* Acquire a write lock on a read-write-lock object.
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*
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* Input Parameters:
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* rwsem - Pointer to the read-write-lock descriptor.
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*
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* Returned Value:
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* Return 1 if successful, 0 if failed
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*
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****************************************************************************/
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int down_write_trylock(FAR rw_semaphore_t *rwsem)
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{
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pid_t tid = _SCHED_GETTID();
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nxmutex_lock(&rwsem->protected);
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if (rwsem->reader > 0 || (rwsem->writer > 0 && tid != rwsem->holder))
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{
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nxmutex_unlock(&rwsem->protected);
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return 0;
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}
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/* The check passes, then we just need the writer reference + 1 */
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rwsem->writer++;
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rwsem->holder = tid;
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nxmutex_unlock(&rwsem->protected);
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return 1;
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}
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/****************************************************************************
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* Name: down_write
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*
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* Description:
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* Acquire a write lock on a read-write-lock object.
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*
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* Input Parameters:
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* rwsem - Pointer to the read-write-lock descriptor.
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*
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****************************************************************************/
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void down_write(FAR rw_semaphore_t *rwsem)
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{
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pid_t tid = _SCHED_GETTID();
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nxmutex_lock(&rwsem->protected);
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while (rwsem->reader > 0 || (rwsem->writer > 0 && rwsem->holder != tid))
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{
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rwsem->waiter++;
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nxmutex_unlock(&rwsem->protected);
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nxsem_wait(&rwsem->waiting);
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nxmutex_lock(&rwsem->protected);
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rwsem->waiter--;
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}
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/* The check passes, then we just need the writer reference + 1 */
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rwsem->writer++;
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rwsem->holder = tid;
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nxmutex_unlock(&rwsem->protected);
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}
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/****************************************************************************
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* Name: up_write
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*
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* Description:
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* Unlock a write lock on a read-write-lock object.
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*
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* Input Parameters:
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* rwsem - Pointer to the read-write-lock descriptor.
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*
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****************************************************************************/
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void up_write(FAR rw_semaphore_t *rwsem)
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{
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nxmutex_lock(&rwsem->protected);
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DEBUGASSERT(rwsem->writer > 0);
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DEBUGASSERT(rwsem->holder == _SCHED_GETTID());
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if (--rwsem->writer <= 0)
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{
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rwsem->holder = RWSEM_NO_HOLDER;
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}
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up_wait(rwsem);
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nxmutex_unlock(&rwsem->protected);
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}
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/****************************************************************************
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* Name: init_rwsem
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*
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* Description:
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* Initialize a read-write-lock object, setting its initial state.
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*
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* Input Parameters:
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* rwsem - Pointer to the read-write-lock descriptor.
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*
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* Returned Value:
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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 init_rwsem(FAR rw_semaphore_t *rwsem)
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{
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int ret;
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/* Initialize structure information */
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ret = nxmutex_init(&rwsem->protected);
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if (ret < 0)
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{
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return ret;
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}
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ret = nxsem_init(&rwsem->waiting, 0, 0);
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if (ret < 0)
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{
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nxmutex_destroy(&rwsem->protected);
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return ret;
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}
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rwsem->reader = 0;
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rwsem->writer = 0;
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rwsem->waiter = 0;
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rwsem->holder = RWSEM_NO_HOLDER;
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return OK;
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}
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/****************************************************************************
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* Name: destroy_rwsem
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*
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* Description:
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* Destroy a read-write-lock object, freeing any resources associated with
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* it.
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*
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* Input Parameters:
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* rwsem - Pointer to the read-write-lock descriptor.
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*
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****************************************************************************/
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void destroy_rwsem(FAR rw_semaphore_t *rwsem)
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{
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/* Need to check if there is still an unlocked or waiting state */
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DEBUGASSERT(rwsem->waiter == 0 && rwsem->reader == 0 &&
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rwsem->writer == 0 && rwsem->holder == RWSEM_NO_HOLDER);
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nxmutex_destroy(&rwsem->protected);
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nxsem_destroy(&rwsem->waiting);
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}
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