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 <stddef.h>
  29 #include <stdint.h>
  30
  31 /**
  32  * @defgroup lavu_buffer AVBuffer
  33  * @ingroup lavu_data
  34  *
  35  * @{
  36  * AVBuffer is an API for reference-counted data buffers.
  37  *
  38  * There are two core objects in this API -- AVBuffer and AVBufferRef. AVBuffer
  39  * represents the data buffer itself; it is opaque and not meant to be accessed
  40  * by the caller directly, but only through AVBufferRef. However, the caller may
  41  * e.g. compare two AVBuffer pointers to check whether two different references
  42  * are describing the same data buffer. AVBufferRef represents a single
  43  * reference to an AVBuffer and it is the object that may be manipulated by the
  44  * caller directly.
  45  *
  46  * There are two functions provided for creating a new AVBuffer with a single
  47  * reference -- av_buffer_alloc() to just allocate a new buffer, and
  48  * av_buffer_create() to wrap an existing array in an AVBuffer. From an existing
  49  * reference, additional references may be created with av_buffer_ref().
  50  * Use av_buffer_unref() to free a reference (this will automatically free the
  51  * data once all the references are freed).
  52  *
  53  * The convention throughout this API and the rest of FFmpeg is such that the
  54  * buffer is considered writable if there exists only one reference to it (and
  55  * it has not been marked as read-only). The av_buffer_is_writable() function is
  56  * provided to check whether this is true and av_buffer_make_writable() will
  57  * automatically create a new writable buffer when necessary.
  58  * Of course nothing prevents the calling code from violating this convention,
  59  * however that is safe only when all the existing references are under its
  60  * control.
  61  *
  62  * @note Referencing and unreferencing the buffers is thread-safe and thus
  63  * may be done from multiple threads simultaneously without any need for
  64  * additional locking.
  65  *
  66  * @note Two different references to the same buffer can point to different
  67  * parts of the buffer (i.e. their AVBufferRef.data will not be equal).
  68  */
  69
  70 /**
  71  * A reference counted buffer type. It is opaque and is meant to be used through
  72  * references (AVBufferRef).
  73  */
  74 typedef struct AVBuffer AVBuffer;
  75
  76 /**
  77  * A reference to a data buffer.
  78  *
  79  * The size of this struct is not a part of the public ABI and it is not meant
  80  * to be allocated directly.
  81  */
  82 typedef struct AVBufferRef {
  83     AVBuffer *buffer;
  84
  85     /**
  86      * The data buffer. It is considered writable if and only if
  87      * this is the only reference to the buffer, in which case
  88      * av_buffer_is_writable() returns 1.
  89      */
  90     uint8_t *data;
  91     /**
  92      * Size of data in bytes.
  93      */
  94     size_t   size;
  95 } AVBufferRef;
  96
  97 /**
  98  * Allocate an AVBuffer of the given size using av_malloc().
  99  *
 100  * @return an AVBufferRef of given size or NULL when out of memory
 101  */
 102 AVBufferRef *av_buffer_alloc(size_t size);
 103
 104 /**
 105  * Same as av_buffer_alloc(), except the returned buffer will be initialized
 106  * to zero.
 107  */
 108 AVBufferRef *av_buffer_allocz(size_t size);
 109
 110 /**
 111  * Always treat the buffer as read-only, even when it has only one
 112  * reference.
 113  */
 114 #define AV_BUFFER_FLAG_READONLY (1 << 0)
 115
 116 /**
 117  * Create an AVBuffer from an existing array.
 118  *
 119  * If this function is successful, data is owned by the AVBuffer. The caller may
 120  * only access data through the returned AVBufferRef and references derived from
 121  * it.
 122  * If this function fails, data is left untouched.
 123  * @param data   data array
 124  * @param size   size of data in bytes
 125  * @param free   a callback for freeing this buffer's data
 126  * @param opaque parameter to be got for processing or passed to free
 127  * @param flags  a combination of AV_BUFFER_FLAG_*
 128  *
 129  * @return an AVBufferRef referring to data on success, NULL on failure.
 130  */
 131 AVBufferRef *av_buffer_create(uint8_t *data, size_t size,
 132                               void (*free)(void *opaque, uint8_t *data),
 133                               void *opaque, int flags);
 134
 135 /**
 136  * Default free callback, which calls av_free() on the buffer data.
 137  * This function is meant to be passed to av_buffer_create(), not called
 138  * directly.
 139  */
 140 void av_buffer_default_free(void *opaque, uint8_t *data);
 141
 142 /**
 143  * Create a new reference to an AVBuffer.
 144  *
 145  * @return a new AVBufferRef referring to the same AVBuffer as buf or NULL on
 146  * failure.
 147  */
 148 AVBufferRef *av_buffer_ref(const AVBufferRef *buf);
 149
 150 /**
 151  * Free a given reference and automatically free the buffer if there are no more
 152  * references to it.
 153  *
 154  * @param buf the reference to be freed. The pointer is set to NULL on return.
 155  */
 156 void av_buffer_unref(AVBufferRef **buf);
 157
 158 /**
 159  * @return 1 if the caller may write to the data referred to by buf (which is
 160  * true if and only if buf is the only reference to the underlying AVBuffer).
 161  * Return 0 otherwise.
 162  * A positive answer is valid until av_buffer_ref() is called on buf.
 163  */
 164 int av_buffer_is_writable(const AVBufferRef *buf);
 165
 166 /**
 167  * @return the opaque parameter set by av_buffer_create.
 168  */
 169 void *av_buffer_get_opaque(const AVBufferRef *buf);
 170
 171 int av_buffer_get_ref_count(const AVBufferRef *buf);
 172
 173 /**
 174  * Create a writable reference from a given buffer reference, avoiding data copy
 175  * if possible.
 176  *
 177  * @param buf buffer reference to make writable. On success, buf is either left
 178  *            untouched, or it is unreferenced and a new writable AVBufferRef is
 179  *            written in its place. On failure, buf is left untouched.
 180  * @return 0 on success, a negative AVERROR on failure.
 181  */
 182 int av_buffer_make_writable(AVBufferRef **buf);
 183
 184 /**
 185  * Reallocate a given buffer.
 186  *
 187  * @param buf  a buffer reference to reallocate. On success, buf will be
 188  *             unreferenced and a new reference with the required size will be
 189  *             written in its place. On failure buf will be left untouched. *buf
 190  *             may be NULL, then a new buffer is allocated.
 191  * @param size required new buffer size.
 192  * @return 0 on success, a negative AVERROR on failure.
 193  *
 194  * @note the buffer is actually reallocated with av_realloc() only if it was
 195  * initially allocated through av_buffer_realloc(NULL) and there is only one
 196  * reference to it (i.e. the one passed to this function). In all other cases
 197  * a new buffer is allocated and the data is copied.
 198  */
 199 int av_buffer_realloc(AVBufferRef **buf, size_t size);
 200
 201 /**
 202  * Ensure dst refers to the same data as src.
 203  *
 204  * When *dst is already equivalent to src, do nothing. Otherwise unreference dst
 205  * and replace it with a new reference to src.
 206  *
 207  * @param dst Pointer to either a valid buffer reference or NULL. On success,
 208  *            this will point to a buffer reference equivalent to src. On
 209  *            failure, dst will be left untouched.
 210  * @param src A buffer reference to replace dst with. May be NULL, then this
 211  *            function is equivalent to av_buffer_unref(dst).
 212  * @return 0 on success
 213  *         AVERROR(ENOMEM) on memory allocation failure.
 214  */
 215 int av_buffer_replace(AVBufferRef **dst, const AVBufferRef *src);
 216
 217 /**
 218  * @}
 219  */
 220
 221 /**
 222  * @defgroup lavu_bufferpool AVBufferPool
 223  * @ingroup lavu_data
 224  *
 225  * @{
 226  * AVBufferPool is an API for a lock-free thread-safe pool of AVBuffers.
 227  *
 228  * Frequently allocating and freeing large buffers may be slow. AVBufferPool is
 229  * meant to solve this in cases when the caller needs a set of buffers of the
 230  * same size (the most obvious use case being buffers for raw video or audio
 231  * frames).
 232  *
 233  * At the beginning, the user must call av_buffer_pool_init() to create the
 234  * buffer pool. Then whenever a buffer is needed, call av_buffer_pool_get() to
 235  * get a reference to a new buffer, similar to av_buffer_alloc(). This new
 236  * reference works in all aspects the same way as the one created by
 237  * av_buffer_alloc(). However, when the last reference to this buffer is
 238  * unreferenced, it is returned to the pool instead of being freed and will be
 239  * reused for subsequent av_buffer_pool_get() calls.
 240  *
 241  * When the caller is done with the pool and no longer needs to allocate any new
 242  * buffers, av_buffer_pool_uninit() must be called to mark the pool as freeable.
 243  * Once all the buffers are released, it will automatically be freed.
 244  *
 245  * Allocating and releasing buffers with this API is thread-safe as long as
 246  * either the default alloc callback is used, or the user-supplied one is
 247  * thread-safe.
 248  */
 249
 250 /**
 251  * The buffer pool. This structure is opaque and not meant to be accessed
 252  * directly. It is allocated with av_buffer_pool_init() and freed with
 253  * av_buffer_pool_uninit().
 254  */
 255 typedef struct AVBufferPool AVBufferPool;
 256
 257 /**
 258  * Allocate and initialize a buffer pool.
 259  *
 260  * @param size size of each buffer in this pool
 261  * @param alloc a function that will be used to allocate new buffers when the
 262  * pool is empty. May be NULL, then the default allocator will be used
 263  * (av_buffer_alloc()).
 264  * @return newly created buffer pool on success, NULL on error.
 265  */
 266 AVBufferPool *av_buffer_pool_init(size_t size, AVBufferRef* (*alloc)(size_t size));
 267
 268 /**
 269  * Allocate and initialize a buffer pool with a more complex allocator.
 270  *
 271  * @param size size of each buffer in this pool
 272  * @param opaque arbitrary user data used by the allocator
 273  * @param alloc a function that will be used to allocate new buffers when the
 274  *              pool is empty. May be NULL, then the default allocator will be
 275  *              used (av_buffer_alloc()).
 276  * @param pool_free a function that will be called immediately before the pool
 277  *                  is freed. I.e. after av_buffer_pool_uninit() is called
 278  *                  by the caller and all the frames are returned to the pool
 279  *                  and freed. It is intended to uninitialize the user opaque
 280  *                  data. May be NULL.
 281  * @return newly created buffer pool on success, NULL on error.
 282  */
 283 AVBufferPool *av_buffer_pool_init2(size_t size, void *opaque,
 284                                    AVBufferRef* (*alloc)(void *opaque, size_t size),
 285                                    void (*pool_free)(void *opaque));
 286
 287 /**
 288  * Mark the pool as being available for freeing. It will actually be freed only
 289  * once all the allocated buffers associated with the pool are released. Thus it
 290  * is safe to call this function while some of the allocated buffers are still
 291  * in use.
 292  *
 293  * @param pool pointer to the pool to be freed. It will be set to NULL.
 294  */
 295 void av_buffer_pool_uninit(AVBufferPool **pool);
 296
 297 /**
 298  * Allocate a new AVBuffer, reusing an old buffer from the pool when available.
 299  * This function may be called simultaneously from multiple threads.
 300  *
 301  * @return a reference to the new buffer on success, NULL on error.
 302  */
 303 AVBufferRef *av_buffer_pool_get(AVBufferPool *pool);
 304
 305 /**
 306  * Query the original opaque parameter of an allocated buffer in the pool.
 307  *
 308  * @param ref a buffer reference to a buffer returned by av_buffer_pool_get.
 309  * @return the opaque parameter set by the buffer allocator function of the
 310  *         buffer pool.
 311  *
 312  * @note the opaque parameter of ref is used by the buffer pool implementation,
 313  * therefore you have to use this function to access the original opaque
 314  * parameter of an allocated buffer.
 315  */
 316 void *av_buffer_pool_buffer_get_opaque(const AVBufferRef *ref);
 317
 318 /**
 319  * @}
 320  */
 321
 322 #endif /* AVUTIL_BUFFER_H */