ffmpeg/libavutil/buffer.h

   1 /*
   2  * This file is part of FFmpeg.
   3  *
   4  * FFmpeg is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2.1 of the License, or (at your option) any later version.
   8  *
   9  * FFmpeg is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with FFmpeg; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  17  */
  18
  19 /**
  20  * @file
  21  * @ingroup lavu_buffer
  22  * refcounted data buffer API
  23  */
  24
  25 #ifndef AVUTIL_BUFFER_H
  26 #define AVUTIL_BUFFER_H
  27
  28 #include <stdint.h>
  29
  30 /**
  31  * @defgroup lavu_buffer AVBuffer
  32  * @ingroup lavu_data
  33  *
  34  * @{
  35  * AVBuffer is an API for reference-counted data buffers.
  36  *
  37  * There are two core objects in this API -- AVBuffer and AVBufferRef. AVBuffer
  38  * represents the data buffer itself; it is opaque and not meant to be accessed
  39  * by the caller directly, but only through AVBufferRef. However, the caller may
  40  * e.g. compare two AVBuffer pointers to check whether two different references
  41  * are describing the same data buffer. AVBufferRef represents a single
  42  * reference to an AVBuffer and it is the object that may be manipulated by the
  43  * caller directly.
  44  *
  45  * There are two functions provided for creating a new AVBuffer with a single
  46  * reference -- av_buffer_alloc() to just allocate a new buffer, and
  47  * av_buffer_create() to wrap an existing array in an AVBuffer. From an existing
  48  * reference, additional references may be created with av_buffer_ref().
  49  * Use av_buffer_unref() to free a reference (this will automatically free the
  50  * data once all the references are freed).
  51  *
  52  * The convention throughout this API and the rest of FFmpeg is such that the
  53  * buffer is considered writable if there exists only one reference to it (and
  54  * it has not been marked as read-only). The av_buffer_is_writable() function is
  55  * provided to check whether this is true and av_buffer_make_writable() will
  56  * automatically create a new writable buffer when necessary.
  57  * Of course nothing prevents the calling code from violating this convention,
  58  * however that is safe only when all the existing references are under its
  59  * control.
  60  *
  61  * @note Referencing and unreferencing the buffers is thread-safe and thus
  62  * may be done from multiple threads simultaneously without any need for
  63  * additional locking.
  64  *
  65  * @note Two different references to the same buffer can point to different
  66  * parts of the buffer (i.e. their AVBufferRef.data will not be equal).
  67  */
  68
  69 /**
  70  * A reference counted buffer type. It is opaque and is meant to be used through
  71  * references (AVBufferRef).
  72  */
  73 typedef struct AVBuffer AVBuffer;
  74
  75 /**
  76  * A reference to a data buffer.
  77  *
  78  * The size of this struct is not a part of the public ABI and it is not meant
  79  * to be allocated directly.
  80  */
  81 typedef struct AVBufferRef {
  82     AVBuffer *buffer;
  83
  84     /**
  85      * The data buffer. It is considered writable if and only if
  86      * this is the only reference to the buffer, in which case
  87      * av_buffer_is_writable() returns 1.
  88      */
  89     uint8_t *data;
  90     /**
  91      * Size of data in bytes.
  92      */
  93     int      size;
  94 } AVBufferRef;
  95
  96 /**
  97  * Allocate an AVBuffer of the given size using av_malloc().
  98  *
  99  * @return an AVBufferRef of given size or NULL when out of memory
 100  */
 101 AVBufferRef *av_buffer_alloc(int size);
 102
 103 /**
 104  * Same as av_buffer_alloc(), except the returned buffer will be initialized
 105  * to zero.
 106  */
 107 AVBufferRef *av_buffer_allocz(int size);
 108
 109 /**
 110  * Always treat the buffer as read-only, even when it has only one
 111  * reference.
 112  */
 113 #define AV_BUFFER_FLAG_READONLY (1 << 0)
 114
 115 /**
 116  * Create an AVBuffer from an existing array.
 117  *
 118  * If this function is successful, data is owned by the AVBuffer. The caller may
 119  * only access data through the returned AVBufferRef and references derived from
 120  * it.
 121  * If this function fails, data is left untouched.
 122  * @param data   data array
 123  * @param size   size of data in bytes
 124  * @param free   a callback for freeing this buffer's data
 125  * @param opaque parameter to be got for processing or passed to free
 126  * @param flags  a combination of AV_BUFFER_FLAG_*
 127  *
 128  * @return an AVBufferRef referring to data on success, NULL on failure.
 129  */
 130 AVBufferRef *av_buffer_create(uint8_t *data, int size,
 131                               void (*free)(void *opaque, uint8_t *data),
 132                               void *opaque, int flags);
 133
 134 /**
 135  * Default free callback, which calls av_free() on the buffer data.
 136  * This function is meant to be passed to av_buffer_create(), not called
 137  * directly.
 138  */
 139 void av_buffer_default_free(void *opaque, uint8_t *data);
 140
 141 /**
 142  * Create a new reference to an AVBuffer.
 143  *
 144  * @return a new AVBufferRef referring to the same AVBuffer as buf or NULL on
 145  * failure.
 146  */
 147 AVBufferRef *av_buffer_ref(AVBufferRef *buf);
 148
 149 /**
 150  * Free a given reference and automatically free the buffer if there are no more
 151  * references to it.
 152  *
 153  * @param buf the reference to be freed. The pointer is set to NULL on return.
 154  */
 155 void av_buffer_unref(AVBufferRef **buf);
 156
 157 /**
 158  * @return 1 if the caller may write to the data referred to by buf (which is
 159  * true if and only if buf is the only reference to the underlying AVBuffer).
 160  * Return 0 otherwise.
 161  * A positive answer is valid until av_buffer_ref() is called on buf.
 162  */
 163 int av_buffer_is_writable(const AVBufferRef *buf);
 164
 165 /**
 166  * @return the opaque parameter set by av_buffer_create.
 167  */
 168 void *av_buffer_get_opaque(const AVBufferRef *buf);
 169
 170 int av_buffer_get_ref_count(const AVBufferRef *buf);
 171
 172 /**
 173  * Create a writable reference from a given buffer reference, avoiding data copy
 174  * if possible.
 175  *
 176  * @param buf buffer reference to make writable. On success, buf is either left
 177  *            untouched, or it is unreferenced and a new writable AVBufferRef is
 178  *            written in its place. On failure, buf is left untouched.
 179  * @return 0 on success, a negative AVERROR on failure.
 180  */
 181 int av_buffer_make_writable(AVBufferRef **buf);
 182
 183 /**
 184  * Reallocate a given buffer.
 185  *
 186  * @param buf  a buffer reference to reallocate. On success, buf will be
 187  *             unreferenced and a new reference with the required size will be
 188  *             written in its place. On failure buf will be left untouched. *buf
 189  *             may be NULL, then a new buffer is allocated.
 190  * @param size required new buffer size.
 191  * @return 0 on success, a negative AVERROR on failure.
 192  *
 193  * @note the buffer is actually reallocated with av_realloc() only if it was
 194  * initially allocated through av_buffer_realloc(NULL) and there is only one
 195  * reference to it (i.e. the one passed to this function). In all other cases
 196  * a new buffer is allocated and the data is copied.
 197  */
 198 int av_buffer_realloc(AVBufferRef **buf, int size);
 199
 200 /**
 201  * @}
 202  */
 203
 204 /**
 205  * @defgroup lavu_bufferpool AVBufferPool
 206  * @ingroup lavu_data
 207  *
 208  * @{
 209  * AVBufferPool is an API for a lock-free thread-safe pool of AVBuffers.
 210  *
 211  * Frequently allocating and freeing large buffers may be slow. AVBufferPool is
 212  * meant to solve this in cases when the caller needs a set of buffers of the
 213  * same size (the most obvious use case being buffers for raw video or audio
 214  * frames).
 215  *
 216  * At the beginning, the user must call av_buffer_pool_init() to create the
 217  * buffer pool. Then whenever a buffer is needed, call av_buffer_pool_get() to
 218  * get a reference to a new buffer, similar to av_buffer_alloc(). This new
 219  * reference works in all aspects the same way as the one created by
 220  * av_buffer_alloc(). However, when the last reference to this buffer is
 221  * unreferenced, it is returned to the pool instead of being freed and will be
 222  * reused for subsequent av_buffer_pool_get() calls.
 223  *
 224  * When the caller is done with the pool and no longer needs to allocate any new
 225  * buffers, av_buffer_pool_uninit() must be called to mark the pool as freeable.
 226  * Once all the buffers are released, it will automatically be freed.
 227  *
 228  * Allocating and releasing buffers with this API is thread-safe as long as
 229  * either the default alloc callback is used, or the user-supplied one is
 230  * thread-safe.
 231  */
 232
 233 /**
 234  * The buffer pool. This structure is opaque and not meant to be accessed
 235  * directly. It is allocated with av_buffer_pool_init() and freed with
 236  * av_buffer_pool_uninit().
 237  */
 238 typedef struct AVBufferPool AVBufferPool;
 239
 240 /**
 241  * Allocate and initialize a buffer pool.
 242  *
 243  * @param size size of each buffer in this pool
 244  * @param alloc a function that will be used to allocate new buffers when the
 245  * pool is empty. May be NULL, then the default allocator will be used
 246  * (av_buffer_alloc()).
 247  * @return newly created buffer pool on success, NULL on error.
 248  */
 249 AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size));
 250
 251 /**
 252  * Mark the pool as being available for freeing. It will actually be freed only
 253  * once all the allocated buffers associated with the pool are released. Thus it
 254  * is safe to call this function while some of the allocated buffers are still
 255  * in use.
 256  *
 257  * @param pool pointer to the pool to be freed. It will be set to NULL.
 258  * @see av_buffer_pool_can_uninit()
 259  */
 260 void av_buffer_pool_uninit(AVBufferPool **pool);
 261
 262 /**
 263  * Allocate a new AVBuffer, reusing an old buffer from the pool when available.
 264  * This function may be called simultaneously from multiple threads.
 265  *
 266  * @return a reference to the new buffer on success, NULL on error.
 267  */
 268 AVBufferRef *av_buffer_pool_get(AVBufferPool *pool);
 269
 270 /**
 271  * @}
 272  */
 273
 274 #endif /* AVUTIL_BUFFER_H */