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/*
* This file is part of FFmpeg.
*
* FFmpeg 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.
*
* FFmpeg 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 FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stdatomic.h>
#include <stdint.h>
#include <string.h>
#include "internal.h"
#include "refstruct.h"
#include "libavutil/avassert.h"
#include "libavutil/macros.h"
#include "libavutil/mem.h"
#ifndef REFSTRUCT_CHECKED
#ifndef ASSERT_LEVEL
#define ASSERT_LEVEL 0
#endif
#define REFSTRUCT_CHECKED (ASSERT_LEVEL >= 1)
#endif
#if REFSTRUCT_CHECKED
#define ff_assert(cond) av_assert0(cond)
#else
#define ff_assert(cond) ((void)0)
#endif
#define REFSTRUCT_COOKIE AV_NE((uint64_t)MKBETAG('R', 'e', 'f', 'S') << 32 | MKBETAG('t', 'r', 'u', 'c'), \
MKTAG('R', 'e', 'f', 'S') | (uint64_t)MKTAG('t', 'r', 'u', 'c') << 32)
#if __STDC_VERSION__ >= 201112L
#define REFCOUNT_OFFSET FFALIGN(sizeof(RefCount), FFMAX3(STRIDE_ALIGN, 16, _Alignof(max_align_t)))
#else
#define REFCOUNT_OFFSET FFALIGN(sizeof(RefCount), FFMAX(STRIDE_ALIGN, 16))
#endif
typedef struct RefCount {
/**
* An uintptr_t is big enough to hold the address of every reference,
* so no overflow can happen when incrementing the refcount as long as
* the user does not throw away references.
*/
atomic_uintptr_t refcount;
FFRefStructOpaque opaque;
void (*free_cb)(FFRefStructOpaque opaque, void *obj);
#if REFSTRUCT_CHECKED
uint64_t cookie;
#endif
} RefCount;
static RefCount *get_refcount(void *obj)
{
RefCount *ref = (RefCount*)((char*)obj - REFCOUNT_OFFSET);
ff_assert(ref->cookie == REFSTRUCT_COOKIE);
return ref;
}
static const RefCount *cget_refcount(const void *obj)
{
const RefCount *ref = (const RefCount*)((const char*)obj - REFCOUNT_OFFSET);
ff_assert(ref->cookie == REFSTRUCT_COOKIE);
return ref;
}
static void *get_userdata(void *buf)
{
return (char*)buf + REFCOUNT_OFFSET;
}
static void refcount_init(RefCount *ref, FFRefStructOpaque opaque,
void (*free_cb)(FFRefStructOpaque opaque, void *obj))
{
atomic_init(&ref->refcount, 1);
ref->opaque = opaque;
ref->free_cb = free_cb;
#if REFSTRUCT_CHECKED
ref->cookie = REFSTRUCT_COOKIE;
#endif
}
void *ff_refstruct_alloc_ext_c(size_t size, unsigned flags, FFRefStructOpaque opaque,
void (*free_cb)(FFRefStructOpaque opaque, void *obj))
{
void *buf, *obj;
if (size > SIZE_MAX - REFCOUNT_OFFSET)
return NULL;
buf = av_malloc(size + REFCOUNT_OFFSET);
if (!buf)
return NULL;
refcount_init(buf, opaque, free_cb);
obj = get_userdata(buf);
if (!(flags & FF_REFSTRUCT_FLAG_NO_ZEROING))
memset(obj, 0, size);
return obj;
}
void ff_refstruct_unref(void *objp)
{
void *obj;
RefCount *ref;
memcpy(&obj, objp, sizeof(obj));
if (!obj)
return;
memcpy(objp, &(void *){ NULL }, sizeof(obj));
ref = get_refcount(obj);
if (atomic_fetch_sub_explicit(&ref->refcount, 1, memory_order_acq_rel) == 1) {
if (ref->free_cb)
ref->free_cb(ref->opaque, obj);
av_free(ref);
}
return;
}
void *ff_refstruct_ref(void *obj)
{
RefCount *ref = get_refcount(obj);
atomic_fetch_add_explicit(&ref->refcount, 1, memory_order_relaxed);
return obj;
}
const void *ff_refstruct_ref_c(const void *obj)
{
/* Casting const away here is fine, as it is only supposed
* to apply to the user's data and not our bookkeeping data. */
RefCount *ref = get_refcount((void*)obj);
atomic_fetch_add_explicit(&ref->refcount, 1, memory_order_relaxed);
return obj;
}
void ff_refstruct_replace(void *dstp, const void *src)
{
const void *dst;
memcpy(&dst, dstp, sizeof(dst));
if (src == dst)
return;
ff_refstruct_unref(dstp);
if (src) {
dst = ff_refstruct_ref_c(src);
memcpy(dstp, &dst, sizeof(dst));
}
}
int ff_refstruct_exclusive(const void *obj)
{
const RefCount *ref = cget_refcount(obj);
/* Casting const away here is safe, because it is a load.
* It is necessary because atomic_load_explicit() does not
* accept const atomics in C11 (see also N1807). */
return atomic_load_explicit((atomic_uintptr_t*)&ref->refcount, memory_order_acquire) == 1;
}
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