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 */ 323