[FFmpeg-cvslog] AVBuffer: add a new API for buffer pools
Anton Khirnov
git at videolan.org
Fri Mar 8 16:16:24 CET 2013
ffmpeg | branch: master | Anton Khirnov <anton at khirnov.net> | Sun Jan 20 08:03:13 2013 +0100| [1cec0624d0e6f48590283a57169b58b9fe8449d3] | committer: Anton Khirnov
AVBuffer: add a new API for buffer pools
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=1cec0624d0e6f48590283a57169b58b9fe8449d3
---
libavutil/buffer.c | 143 +++++++++++++++++++++++++++++++++++++++++++
libavutil/buffer.h | 70 +++++++++++++++++++++
libavutil/buffer_internal.h | 32 ++++++++++
3 files changed, 245 insertions(+)
diff --git a/libavutil/buffer.c b/libavutil/buffer.c
index b5e92c9..2b38081 100644
--- a/libavutil/buffer.c
+++ b/libavutil/buffer.c
@@ -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;
+}
diff --git a/libavutil/buffer.h b/libavutil/buffer.h
index 843dfbe..e348c6e 100644
--- a/libavutil/buffer.h
+++ b/libavutil/buffer.h
@@ -194,4 +194,74 @@ 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);
+
+/**
+ * @}
+ */
+
#endif /* AVUTIL_BUFFER_H */
diff --git a/libavutil/buffer_internal.h b/libavutil/buffer_internal.h
index 677c341..cce83c3 100644
--- a/libavutil/buffer_internal.h
+++ b/libavutil/buffer_internal.h
@@ -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 */
More information about the ffmpeg-cvslog
mailing list