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 */ 275