src/shmarea.c - master - niceSOFT/alsa-lib

src/shmarea.c
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01 сен 2023, 17:12
01 сен 2023, 17:12c4680ed
/*
 *  IPC SHM area manager
 *  Copyright (c) 2003 by Jaroslav Kysela <perex@perex.cz>
 *
 *   This library is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Lesser General Public License as
 *   published by the Free Software Foundation; either version 2.1 of
 *   the License, or (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 */

/**
 * \file shmarea.c
 * \ingroup Global
 * \brief shared memory helpers
 * \author Jaroslav Kysela <perex@perex.cz>
 * \date 2001
 *
 * Shared memory helpers
 */

#include "config.h"

/* These funcs are only used by pcm_mmap when sys/shm.h is available. */
#ifdef HAVE_SYS_SHM_H

#include <stdio.h>
#include <stdlib.h>
#if HAVE_MALLOC_H
#include <malloc.h>
#endif
#include <string.h>
#include <errno.h>
#include <poll.h>
#include <sys/mman.h>
#include <sys/shm.h>
#include "list.h"

#ifndef DOC_HIDDEN
struct snd_shm_area {
	struct list_head list;
	int shmid;
	void *ptr;
	int share;
};
#endif

static LIST_HEAD(shm_areas);

/**
 * \brief Create a shm area record
 * \param shmid IPC SHM ID
 * \param ptr the shared area pointer
 * \return The allocated shm area record, NULL if fail
 *
 * Allocates a shared area record with the given SHM ID and pointer.
 * The record has a reference counter, which is initialized to 1 by this function.
 */
struct snd_shm_area *snd_shm_area_create(int shmid, void *ptr)
{
	struct snd_shm_area *area = malloc(sizeof(*area));
	if (area) {
		area->shmid = shmid;
		area->ptr = ptr;
		area->share = 1;
		list_add_tail(&area->list, &shm_areas);
	}
	return area;
}

/**
 * \brief Increase the reference counter of shm area record
 * \param area shm area record
 * \return the shm area record (identical with the argument)
 *
 * Increases the reference counter of the given shared area record.
 */
struct snd_shm_area *snd_shm_area_share(struct snd_shm_area *area)
{
	if (area == NULL)
		return NULL;
	area->share++;
	return area;
}

/**
 * \brief Release the shared area record
 * \param area the shared are record
 * \return 0 if successful, or a negative error code
 *
 * Decreases the reference counter of the given shared area record, and
 * releases the resources automaticall if it reaches to 0.
 */
int snd_shm_area_destroy(struct snd_shm_area *area)
{
	if (area == NULL)
		return -ENOENT;
	if (--area->share)
		return 0;
	list_del(&area->list);
	shmdt(area->ptr);
	free(area);
	return 0;
}

#ifndef DOC_HIDDEN
void snd_shm_area_destructor(void) __attribute__ ((destructor));

void snd_shm_area_destructor(void)
{
	struct list_head *pos;
	struct snd_shm_area *area;

	list_for_each(pos, &shm_areas) {
		area = list_entry(pos, struct snd_shm_area, list);
		shmdt(area->ptr);
	}
}
#endif /* DOC_HIDDEN */

#endif