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