7fc18e09bfdea53ce3bd060a9b3c8371f8c03847
[libav.git] / libavutil / buffer.h
1 /*
2 * This file is part of Libav.
3 *
4 * Libav 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 * Libav 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 Libav; 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 Libav 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 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 * Create a writable reference from a given buffer reference, avoiding data copy
167 * if possible.
168 *
169 * @param buf buffer reference to make writable. On success, buf is either left
170 * untouched, or it is unreferenced and a new writable AVBufferRef is
171 * written in its place. On failure, buf is left untouched.
172 * @return 0 on success, a negative AVERROR on failure.
173 */
174 int av_buffer_make_writable(AVBufferRef **buf);
175
176 /**
177 * Reallocate a given buffer.
178 *
179 * @param buf a buffer reference to reallocate. On success, buf will be
180 * unreferenced and a new reference with the required size will be
181 * written in its place. On failure buf will be left untouched. *buf
182 * may be NULL, then a new buffer is allocated.
183 * @param size required new buffer size.
184 * @return 0 on success, a negative AVERROR on failure.
185 *
186 * @note the buffer is actually reallocated with av_realloc() only if it was
187 * initially allocated through av_buffer_realloc(NULL) and there is only one
188 * reference to it (i.e. the one passed to this function). In all other cases
189 * a new buffer is allocated and the data is copied.
190 */
191 int av_buffer_realloc(AVBufferRef **buf, int size);
192
193 /**
194 * @}
195 */
196
197 /**
198 * @defgroup lavu_bufferpool AVBufferPool
199 * @ingroup lavu_data
200 *
201 * @{
202 * AVBufferPool is an API for a lock-free thread-safe pool of AVBuffers.
203 *
204 * Frequently allocating and freeing large buffers may be slow. AVBufferPool is
205 * meant to solve this in cases when the caller needs a set of buffers of the
206 * same size (the most obvious use case being buffers for raw video or audio
207 * frames).
208 *
209 * At the beginning, the user must call av_buffer_pool_init() to create the
210 * buffer pool. Then whenever a buffer is needed, call av_buffer_pool_get() to
211 * get a reference to a new buffer, similar to av_buffer_alloc(). This new
212 * reference works in all aspects the same way as the one created by
213 * av_buffer_alloc(). However, when the last reference to this buffer is
214 * unreferenced, it is returned to the pool instead of being freed and will be
215 * reused for subsequent av_buffer_pool_get() calls.
216 *
217 * When the caller is done with the pool and no longer needs to allocate any new
218 * buffers, av_buffer_pool_uninit() must be called to mark the pool as freeable.
219 * Once all the buffers are released, it will automatically be freed.
220 *
221 * Allocating and releasing buffers with this API is thread-safe as long as
222 * either the default alloc callback is used, or the user-supplied one is
223 * thread-safe.
224 */
225
226 /**
227 * The buffer pool. This structure is opaque and not meant to be accessed
228 * directly. It is allocated with av_buffer_pool_init() and freed with
229 * av_buffer_pool_uninit().
230 */
231 typedef struct AVBufferPool AVBufferPool;
232
233 /**
234 * Allocate and initialize a buffer pool.
235 *
236 * @param size size of each buffer in this pool
237 * @param alloc a function that will be used to allocate new buffers when the
238 * pool is empty. May be NULL, then the default allocator will be used
239 * (av_buffer_alloc()).
240 * @return newly created buffer pool on success, NULL on error.
241 */
242 AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size));
243
244 /**
245 * Allocate and initialize a buffer pool with a more complex allocator.
246 *
247 * @param size size of each buffer in this pool
248 * @param opaque arbitrary user data used by the allocator
249 * @param alloc a function that will be used to allocate new buffers when the
250 * pool is empty.
251 * @param pool_free a function that will be called immediately before the pool
252 * is freed. I.e. after av_buffer_pool_can_uninit() is called
253 * by the pool and all the frames are returned to the pool and
254 * freed. It is intended to uninitialize the user opaque data.
255 * @return newly created buffer pool on success, NULL on error.
256 */
257 AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
258 AVBufferRef* (*alloc)(void *opaque, int size),
259 void (*pool_free)(void *opaque));
260
261 /**
262 * Mark the pool as being available for freeing. It will actually be freed only
263 * once all the allocated buffers associated with the pool are released. Thus it
264 * is safe to call this function while some of the allocated buffers are still
265 * in use.
266 *
267 * @param pool pointer to the pool to be freed. It will be set to NULL.
268 * @see av_buffer_pool_can_uninit()
269 */
270 void av_buffer_pool_uninit(AVBufferPool **pool);
271
272 /**
273 * Allocate a new AVBuffer, reusing an old buffer from the pool when available.
274 * This function may be called simultaneously from multiple threads.
275 *
276 * @return a reference to the new buffer on success, NULL on error.
277 */
278 AVBufferRef *av_buffer_pool_get(AVBufferPool *pool);
279
280 /**
281 * @}
282 */
283
284 #endif /* AVUTIL_BUFFER_H */