nuttx-update/libs/libc/misc/lib_pathbuffer.c
chenrun1 9138e8af01 lib_pathbuffer.c:Use atomic instead of locks
Summary:
  Use atomic_cmpxchg to ensure that in multithreaded situations, if someone releases the buffer, it can be applied for in time. And use atomic_ulong to save free_bitmap

Signed-off-by: chenrun1 <chenrun1@xiaomi.com>
2024-12-17 09:33:50 +08:00

142 lines
4.7 KiB
C

/****************************************************************************
* libs/libc/misc/lib_pathbuffer.c
*
* SPDX-License-Identifier: Apache-2.0
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <nuttx/atomic.h>
#include <nuttx/lib/lib.h>
#include <stdlib.h>
#include <string.h>
/****************************************************************************
* Pre-processor definitions
****************************************************************************/
/****************************************************************************
* Private Types
****************************************************************************/
struct pathbuffer_s
{
atomic_t free_bitmap; /* Bitmap of free buffer */
char buffer[CONFIG_LIBC_PATHBUFFER_MAX][PATH_MAX];
};
/****************************************************************************
* Private Data
****************************************************************************/
static struct pathbuffer_s g_pathbuffer =
{
(1u << CONFIG_LIBC_PATHBUFFER_MAX) - 1,
};
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: lib_get_pathbuffer
*
* Description:
* The lib_get_pathbuffer() function returns a pointer to a temporary
* buffer. The buffer is allocated from a pool of pre-allocated buffers
* and if the pool is exhausted, a new buffer is allocated through
* kmm_malloc(). The size of the buffer is PATH_MAX, and must freed by
* calling lib_put_pathbuffer().
*
* Returned Value:
* On success, lib_get_pathbuffer() returns a pointer to a temporary
* buffer. On failure, NULL is returned.
*
****************************************************************************/
FAR char *lib_get_pathbuffer(void)
{
for (; ; )
{
int32_t update;
int32_t free_bitmap = atomic_read(&g_pathbuffer.free_bitmap);
int index = ffsl(free_bitmap) - 1;
if (index < 0 || index >= CONFIG_LIBC_PATHBUFFER_MAX)
{
break;
}
update = free_bitmap & ~(1u << index);
if (atomic_cmpxchg(&g_pathbuffer.free_bitmap, &free_bitmap,
update))
{
return g_pathbuffer.buffer[index];
}
}
/* If no free buffer is found, allocate a new one if
* CONFIG_LIBC_PATHBUFFER_MALLOC is enabled
*/
#ifdef CONFIG_LIBC_PATHBUFFER_MALLOC
return lib_malloc(PATH_MAX);
#else
return NULL;
#endif
}
/****************************************************************************
* Name: lib_put_pathbuffer
*
* Description:
* The lib_put_pathbuffer() function frees a temporary buffer that was
* allocated by lib_get_pathbuffer(). If the buffer was allocated
* dynamically, it is freed by calling kmm_free(). Otherwise, the buffer
* is marked as free in the pool of pre-allocated buffers.
*
* Returned Value:
* None
*
****************************************************************************/
void lib_put_pathbuffer(FAR char *buffer)
{
int index = (buffer - &g_pathbuffer.buffer[0][0]) / PATH_MAX;
if (index >= 0 && index < CONFIG_LIBC_PATHBUFFER_MAX)
{
DEBUGASSERT((atomic_read(&g_pathbuffer.free_bitmap) &
(1u << index)) == 0);
atomic_fetch_or_acquire(&g_pathbuffer.free_bitmap, 1u << index);
return;
}
/* Free the buffer if it was dynamically allocated */
#ifdef CONFIG_LIBC_PATHBUFFER_MALLOC
lib_free(buffer);
#endif
}