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ffmpeg/libavcodec/refstruct.c

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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 "refstruct.h"
#include "libavutil/avassert.h"
#include "libavutil/error.h"
#include "libavutil/macros.h"
#include "libavutil/mem.h"
#include "libavutil/mem_internal.h"
#include "libavutil/thread.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 && !defined(_MSC_VER)
#define REFCOUNT_OFFSET FFALIGN(sizeof(RefCount), FFMAX(ALIGN_64, _Alignof(max_align_t)))
#else
#define REFCOUNT_OFFSET FFALIGN(sizeof(RefCount), ALIGN_64)
#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);
void (*free)(void *ref);
#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;
ref->free = av_free;
#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);
ref->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;
}
struct FFRefStructPool {
size_t size;
FFRefStructOpaque opaque;
int (*init_cb)(FFRefStructOpaque opaque, void *obj);
void (*reset_cb)(FFRefStructOpaque opaque, void *obj);
void (*free_entry_cb)(FFRefStructOpaque opaque, void *obj);
void (*free_cb)(FFRefStructOpaque opaque);
int uninited;
unsigned entry_flags;
unsigned pool_flags;
/** The number of outstanding entries not in available_entries. */
atomic_uintptr_t refcount;
/**
* This is a linked list of available entries;
* the RefCount's opaque pointer is used as next pointer
* for available entries.
* While the entries are in use, the opaque is a pointer
* to the corresponding FFRefStructPool.
*/
RefCount *available_entries;
AVMutex mutex;
};
static void pool_free(FFRefStructPool *pool)
{
ff_mutex_destroy(&pool->mutex);
if (pool->free_cb)
pool->free_cb(pool->opaque);
av_free(get_refcount(pool));
}
static void pool_free_entry(FFRefStructPool *pool, RefCount *ref)
{
if (pool->free_entry_cb)
pool->free_entry_cb(pool->opaque, get_userdata(ref));
av_free(ref);
}
static void pool_return_entry(void *ref_)
{
RefCount *ref = ref_;
FFRefStructPool *pool = ref->opaque.nc;
ff_mutex_lock(&pool->mutex);
if (!pool->uninited) {
ref->opaque.nc = pool->available_entries;
pool->available_entries = ref;
ref = NULL;
}
ff_mutex_unlock(&pool->mutex);
if (ref)
pool_free_entry(pool, ref);
if (atomic_fetch_sub_explicit(&pool->refcount, 1, memory_order_acq_rel) == 1)
pool_free(pool);
}
static void pool_reset_entry(FFRefStructOpaque opaque, void *entry)
{
FFRefStructPool *pool = opaque.nc;
pool->reset_cb(pool->opaque, entry);
}
static int refstruct_pool_get_ext(void *datap, FFRefStructPool *pool)
{
void *ret = NULL;
memcpy(datap, &(void *){ NULL }, sizeof(void*));
ff_mutex_lock(&pool->mutex);
ff_assert(!pool->uninited);
if (pool->available_entries) {
RefCount *ref = pool->available_entries;
ret = get_userdata(ref);
pool->available_entries = ref->opaque.nc;
ref->opaque.nc = pool;
atomic_init(&ref->refcount, 1);
}
ff_mutex_unlock(&pool->mutex);
if (!ret) {
RefCount *ref;
ret = ff_refstruct_alloc_ext(pool->size, pool->entry_flags, pool,
pool->reset_cb ? pool_reset_entry : NULL);
if (!ret)
return AVERROR(ENOMEM);
ref = get_refcount(ret);
ref->free = pool_return_entry;
if (pool->init_cb) {
int err = pool->init_cb(pool->opaque, ret);
if (err < 0) {
if (pool->pool_flags & FF_REFSTRUCT_POOL_FLAG_RESET_ON_INIT_ERROR)
pool->reset_cb(pool->opaque, ret);
if (pool->pool_flags & FF_REFSTRUCT_POOL_FLAG_FREE_ON_INIT_ERROR)
pool->free_entry_cb(pool->opaque, ret);
av_free(ref);
return err;
}
}
}
atomic_fetch_add_explicit(&pool->refcount, 1, memory_order_relaxed);
if (pool->pool_flags & FF_REFSTRUCT_POOL_FLAG_ZERO_EVERY_TIME)
memset(ret, 0, pool->size);
memcpy(datap, &ret, sizeof(ret));
return 0;
}
void *ff_refstruct_pool_get(FFRefStructPool *pool)
{
void *ret;
refstruct_pool_get_ext(&ret, pool);
return ret;
}
/**
* Hint: The content of pool_unref() and refstruct_pool_uninit()
* could currently be merged; they are only separate functions
* in case we would ever introduce weak references.
*/
static void pool_unref(void *ref)
{
FFRefStructPool *pool = get_userdata(ref);
if (atomic_fetch_sub_explicit(&pool->refcount, 1, memory_order_acq_rel) == 1)
pool_free(pool);
}
static void refstruct_pool_uninit(FFRefStructOpaque unused, void *obj)
{
FFRefStructPool *pool = obj;
RefCount *entry;
ff_mutex_lock(&pool->mutex);
ff_assert(!pool->uninited);
pool->uninited = 1;
entry = pool->available_entries;
pool->available_entries = NULL;
ff_mutex_unlock(&pool->mutex);
while (entry) {
void *next = entry->opaque.nc;
pool_free_entry(pool, entry);
entry = next;
}
}
FFRefStructPool *ff_refstruct_pool_alloc(size_t size, unsigned flags)
{
return ff_refstruct_pool_alloc_ext(size, flags, NULL, NULL, NULL, NULL, NULL);
}
FFRefStructPool *ff_refstruct_pool_alloc_ext_c(size_t size, unsigned flags,
FFRefStructOpaque opaque,
int (*init_cb)(FFRefStructOpaque opaque, void *obj),
void (*reset_cb)(FFRefStructOpaque opaque, void *obj),
void (*free_entry_cb)(FFRefStructOpaque opaque, void *obj),
void (*free_cb)(FFRefStructOpaque opaque))
{
FFRefStructPool *pool = ff_refstruct_alloc_ext(sizeof(*pool), 0, NULL,
refstruct_pool_uninit);
int err;
if (!pool)
return NULL;
get_refcount(pool)->free = pool_unref;
pool->size = size;
pool->opaque = opaque;
pool->init_cb = init_cb;
pool->reset_cb = reset_cb;
pool->free_entry_cb = free_entry_cb;
pool->free_cb = free_cb;
#define COMMON_FLAGS FF_REFSTRUCT_POOL_FLAG_NO_ZEROING
pool->entry_flags = flags & COMMON_FLAGS;
// Filter out nonsense combinations to avoid checks later.
if (!pool->reset_cb)
flags &= ~FF_REFSTRUCT_POOL_FLAG_RESET_ON_INIT_ERROR;
if (!pool->free_entry_cb)
flags &= ~FF_REFSTRUCT_POOL_FLAG_FREE_ON_INIT_ERROR;
pool->pool_flags = flags;
if (flags & FF_REFSTRUCT_POOL_FLAG_ZERO_EVERY_TIME) {
// We will zero the buffer before every use, so zeroing
// upon allocating the buffer is unnecessary.
pool->entry_flags |= FF_REFSTRUCT_FLAG_NO_ZEROING;
}
atomic_init(&pool->refcount, 1);
err = ff_mutex_init(&pool->mutex, NULL);
if (err) {
// Don't call ff_refstruct_uninit() on pool, as it hasn't been properly
// set up and is just a POD right now.
av_free(get_refcount(pool));
return NULL;
}
return pool;
}
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