text: /*
   * 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
   */
  
  /**
   * @file
   * @ingroup lavu_buffer
   * refcounted data buffer API
   */
  
  #ifndef AVUTIL_BUFFER_H
  #define AVUTIL_BUFFER_H
  
  #include <stdint.h>
  
  /**
   * @defgroup lavu_buffer AVBuffer
   * @ingroup lavu_data
   *
   * @{
   * AVBuffer is an API for reference-counted data buffers.
   *
   * There are two core objects in this API -- AVBuffer and AVBufferRef. AVBuffer
   * represents the data buffer itself; it is opaque and not meant to be accessed
   * by the caller directly, but only through AVBufferRef. However, the caller may
   * e.g. compare two AVBuffer pointers to check whether two different references
   * are describing the same data buffer. AVBufferRef represents a single
   * reference to an AVBuffer and it is the object that may be manipulated by the
   * caller directly.
   *
   * There are two functions provided for creating a new AVBuffer with a single
   * reference -- av_buffer_alloc() to just allocate a new buffer, and
   * av_buffer_create() to wrap an existing array in an AVBuffer. From an existing
   * reference, additional references may be created with av_buffer_ref().
   * Use av_buffer_unref() to free a reference (this will automatically free the
   * data once all the references are freed).
   *
   * The convention throughout this API and the rest of FFmpeg is such that the
   * buffer is considered writable if there exists only one reference to it (and
   * it has not been marked as read-only). The av_buffer_is_writable() function is
   * provided to check whether this is true and av_buffer_make_writable() will
   * automatically create a new writable buffer when necessary.
   * Of course nothing prevents the calling code from violating this convention,
   * however that is safe only when all the existing references are under its
   * control.
   *
   * @note Referencing and unreferencing the buffers is thread-safe and thus
   * may be done from multiple threads simultaneously without any need for
   * additional locking.
   *
   * @note Two different references to the same buffer can point to different
   * parts of the buffer (i.e. their AVBufferRef.data will not be equal).
   */
  
  /**
   * A reference counted buffer type. It is opaque and is meant to be used through
   * references (AVBufferRef).
   */
  typedef struct AVBuffer AVBuffer;
  
  /**
   * A reference to a data buffer.
   *
   * The size of this struct is not a part of the public ABI and it is not meant
   * to be allocated directly.
   */
  typedef struct AVBufferRef {
      AVBuffer *buffer;
  
      /**
       * The data buffer. It is considered writable if and only if
       * this is the only reference to the buffer, in which case
       * av_buffer_is_writable() returns 1.
       */
      uint8_t *data;
      /**
       * Size of data in bytes.
       */
      int      size;
  } AVBufferRef;
  
  /**
   * Allocate an AVBuffer of the given size using av_malloc().
   *
   * @return an AVBufferRef of given size or NULL when out of memory
   */
  AVBufferRef *av_buffer_alloc(int size);
  
  /**
   * Same as av_buffer_alloc(), except the returned buffer will be initialized
   * to zero.
   */
  AVBufferRef *av_buffer_allocz(int size);
  
  /**
   * Always treat the buffer as read-only, even when it has only one
   * reference.
   */
  #define AV_BUFFER_FLAG_READONLY (1 << 0)
  
  /**
   * Create an AVBuffer from an existing array.
   *
   * If this function is successful, data is owned by the AVBuffer. The caller may
   * only access data through the returned AVBufferRef and references derived from
   * it.
   * If this function fails, data is left untouched.
   * @param data   data array
   * @param size   size of data in bytes
   * @param free   a callback for freeing this buffer's data
   * @param opaque parameter to be got for processing or passed to free
   * @param flags  a combination of AV_BUFFER_FLAG_*
   *
   * @return an AVBufferRef referring to data on success, NULL on failure.
   */
  AVBufferRef *av_buffer_create(uint8_t *data, int size,
                                void (*free)(void *opaque, uint8_t *data),
                                void *opaque, int flags);
  
  /**
   * Default free callback, which calls av_free() on the buffer data.
   * This function is meant to be passed to av_buffer_create(), not called
   * directly.
   */
  void av_buffer_default_free(void *opaque, uint8_t *data);
  
  /**
   * Create a new reference to an AVBuffer.
   *
   * @return a new AVBufferRef referring to the same AVBuffer as buf or NULL on
   * failure.
   */
  AVBufferRef *av_buffer_ref(AVBufferRef *buf);
  
  /**
   * Free a given reference and automatically free the buffer if there are no more
   * references to it.
   *
   * @param buf the reference to be freed. The pointer is set to NULL on return.
   */
  void av_buffer_unref(AVBufferRef **buf);
  
  /**
   * @return 1 if the caller may write to the data referred to by buf (which is
   * true if and only if buf is the only reference to the underlying AVBuffer).
   * Return 0 otherwise.
   * A positive answer is valid until av_buffer_ref() is called on buf.
   */
  int av_buffer_is_writable(const AVBufferRef *buf);
  
  /**
   * @return the opaque parameter set by av_buffer_create.
   */
  void *av_buffer_get_opaque(const AVBufferRef *buf);
  
  int av_buffer_get_ref_count(const AVBufferRef *buf);
  
  /**
   * Create a writable reference from a given buffer reference, avoiding data copy
   * if possible.
   *
   * @param buf buffer reference to make writable. On success, buf is either left
   *            untouched, or it is unreferenced and a new writable AVBufferRef is
   *            written in its place. On failure, buf is left untouched.
   * @return 0 on success, a negative AVERROR on failure.
   */
  int av_buffer_make_writable(AVBufferRef **buf);
  
  /**
   * Reallocate a given buffer.
   *
   * @param buf  a buffer reference to reallocate. On success, buf will be
   *             unreferenced and a new reference with the required size will be
   *             written in its place. On failure buf will be left untouched. *buf
   *             may be NULL, then a new buffer is allocated.
   * @param size required new buffer size.
   * @return 0 on success, a negative AVERROR on failure.
   *
   * @note the buffer is actually reallocated with av_realloc() only if it was
   * initially allocated through av_buffer_realloc(NULL) and there is only one
   * reference to it (i.e. the one passed to this function). In all other cases
   * a new buffer is allocated and the data is copied.
   */
  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));
  
  /**
   * Allocate and initialize a buffer pool with a more complex allocator.
   *
   * @param size size of each buffer in this pool
   * @param opaque arbitrary user data used by the allocator
   * @param alloc a function that will be used to allocate new buffers when the
   *              pool is empty.
   * @param pool_free a function that will be called immediately before the pool
   *                  is freed. I.e. after av_buffer_pool_can_uninit() is called
   *                  by the pool and all the frames are returned to the pool and
   *                  freed. It is intended to uninitialize the user opaque data.
   * @return newly created buffer pool on success, NULL on error.
   */
  AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
                                     AVBufferRef* (*alloc)(void *opaque, int size),
                                     void (*pool_free)(void *opaque));
  
  /**
   * 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.
   */
  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 */
  