Commit 1cec0624 authored by Anton Khirnov's avatar Anton Khirnov
Browse files

AVBuffer: add a new API for buffer pools

parent 8e401dbe
......@@ -192,3 +192,146 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
buf->buffer->size = buf->size = size;
return 0;
}
AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size))
{
AVBufferPool *pool = av_mallocz(sizeof(*pool));
if (!pool)
return NULL;
pool->size = size;
pool->alloc = alloc ? alloc : av_buffer_alloc;
avpriv_atomic_int_set(&pool->refcount, 1);
return pool;
}
/*
* This function gets called when the pool has been uninited and
* all the buffers returned to it.
*/
static void buffer_pool_free(AVBufferPool *pool)
{
while (pool->pool) {
BufferPoolEntry *buf = pool->pool;
pool->pool = buf->next;
buf->free(buf->opaque, buf->data);
av_freep(&buf);
}
av_freep(&pool);
}
void av_buffer_pool_uninit(AVBufferPool **ppool)
{
AVBufferPool *pool;
if (!ppool || !*ppool)
return;
pool = *ppool;
*ppool = NULL;
if (!avpriv_atomic_int_add_and_fetch(&pool->refcount, -1))
buffer_pool_free(pool);
}
/* remove the whole buffer list from the pool and return it */
static BufferPoolEntry *get_pool(AVBufferPool *pool)
{
BufferPoolEntry *cur = NULL, *last = NULL;
do {
FFSWAP(BufferPoolEntry*, cur, last);
cur = avpriv_atomic_ptr_cas((void * volatile *)&pool->pool, last, NULL);
if (!cur)
return NULL;
} while (cur != last);
return cur;
}
static void add_to_pool(BufferPoolEntry *buf)
{
AVBufferPool *pool;
BufferPoolEntry *cur, *end = buf;
if (!buf)
return;
pool = buf->pool;
while (end->next)
end = end->next;
while ((cur = avpriv_atomic_ptr_cas((void * volatile *)&pool->pool, NULL, buf))) {
/* pool is not empty, retrieve it and append it to our list */
cur = get_pool(pool);
end->next = cur;
while (end->next)
end = end->next;
}
}
static void pool_release_buffer(void *opaque, uint8_t *data)
{
BufferPoolEntry *buf = opaque;
AVBufferPool *pool = buf->pool;
add_to_pool(buf);
if (!avpriv_atomic_int_add_and_fetch(&pool->refcount, -1))
buffer_pool_free(pool);
}
/* allocate a new buffer and override its free() callback so that
* it is returned to the pool on free */
static AVBufferRef *pool_alloc_buffer(AVBufferPool *pool)
{
BufferPoolEntry *buf;
AVBufferRef *ret;
ret = pool->alloc(pool->size);
if (!ret)
return NULL;
buf = av_mallocz(sizeof(*buf));
if (!buf) {
av_buffer_unref(&ret);
return NULL;
}
buf->data = ret->buffer->data;
buf->opaque = ret->buffer->opaque;
buf->free = ret->buffer->free;
buf->pool = pool;
ret->buffer->opaque = buf;
ret->buffer->free = pool_release_buffer;
avpriv_atomic_int_add_and_fetch(&pool->refcount, 1);
return ret;
}
AVBufferRef *av_buffer_pool_get(AVBufferPool *pool)
{
AVBufferRef *ret;
BufferPoolEntry *buf;
/* check whether the pool is empty */
buf = get_pool(pool);
if (!buf)
return pool_alloc_buffer(pool);
/* keep the first entry, return the rest of the list to the pool */
add_to_pool(buf->next);
buf->next = NULL;
ret = av_buffer_create(buf->data, pool->size, pool_release_buffer,
buf, 0);
if (!ret) {
add_to_pool(buf);
return NULL;
}
avpriv_atomic_int_add_and_fetch(&pool->refcount, 1);
return ret;
}
......@@ -190,6 +190,76 @@ int av_buffer_make_writable(AVBufferRef **buf);
*/
int av_buffer_realloc(AVBufferRef **buf, int size);
/**
* @}
*/
/**
* @defgroup lavu_bufferpool AVBufferPool
* @ingroup lavu_data
*
* @{
* AVBufferPool is an API for a lock-free thread-safe pool of AVBuffers.
*
* Frequently allocating and freeing large buffers may be slow. AVBufferPool is
* meant to solve this in cases when the caller needs a set of buffers of the
* same size (the most obvious use case being buffers for raw video or audio
* frames).
*
* At the beginning, the user must call av_buffer_pool_init() to create the
* buffer pool. Then whenever a buffer is needed, call av_buffer_pool_get() to
* get a reference to a new buffer, similar to av_buffer_alloc(). This new
* reference works in all aspects the same way as the one created by
* av_buffer_alloc(). However, when the last reference to this buffer is
* unreferenced, it is returned to the pool instead of being freed and will be
* reused for subsequent av_buffer_pool_get() calls.
*
* When the caller is done with the pool and no longer needs to allocate any new
* buffers, av_buffer_pool_uninit() must be called to mark the pool as freeable.
* Once all the buffers are released, it will automatically be freed.
*
* Allocating and releasing buffers with this API is thread-safe as long as
* either the default alloc callback is used, or the user-supplied one is
* thread-safe.
*/
/**
* The buffer pool. This structure is opaque and not meant to be accessed
* directly. It is allocated with av_buffer_pool_init() and freed with
* av_buffer_pool_uninit().
*/
typedef struct AVBufferPool AVBufferPool;
/**
* Allocate and initialize a buffer pool.
*
* @param size size of each buffer in this pool
* @param alloc a function that will be used to allocate new buffers when the
* pool is empty. May be NULL, then the default allocator will be used
* (av_buffer_alloc()).
* @return newly created buffer pool on success, NULL on error.
*/
AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size));
/**
* Mark the pool as being available for freeing. It will actually be freed only
* once all the allocated buffers associated with the pool are released. Thus it
* is safe to call this function while some of the allocated buffers are still
* in use.
*
* @param pool pointer to the pool to be freed. It will be set to NULL.
* @see av_buffer_pool_can_uninit()
*/
void av_buffer_pool_uninit(AVBufferPool **pool);
/**
* Allocate a new AVBuffer, reusing an old buffer from the pool when available.
* This function may be called simultaneously from multiple threads.
*
* @return a reference to the new buffer on success, NULL on error.
*/
AVBufferRef *av_buffer_pool_get(AVBufferPool *pool);
/**
* @}
*/
......
......@@ -57,4 +57,36 @@ struct AVBuffer {
int flags;
};
typedef struct BufferPoolEntry {
uint8_t *data;
/*
* Backups of the original opaque/free of the AVBuffer corresponding to
* data. They will be used to free the buffer when the pool is freed.
*/
void *opaque;
void (*free)(void *opaque, uint8_t *data);
AVBufferPool *pool;
struct BufferPoolEntry * volatile next;
} BufferPoolEntry;
struct AVBufferPool {
BufferPoolEntry * volatile pool;
/*
* This is used to track when the pool is to be freed.
* The pointer to the pool itself held by the caller is considered to
* be one reference. Each buffer requested by the caller increases refcount
* by one, returning the buffer to the pool decreases it by one.
* refcount reaches zero when the buffer has been uninited AND all the
* buffers have been released, then it's safe to free the pool and all
* the buffers in it.
*/
volatile int refcount;
int size;
AVBufferRef* (*alloc)(int size);
};
#endif /* AVUTIL_BUFFER_INTERNAL_H */
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