tor-browser

buffer.h (9573B)

---

/*
* This file is part of Libav.
*
* Libav 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.
*
* Libav 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 Libav; 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 Libav 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 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);

/**
* 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));

/**
* 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 */