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misc: extreme cleanup, closes #2506 While here, remove unneeded stuff.
author David Demelier <markand@malikania.fr>
date Tue, 20 Oct 2020 17:39:13 +0200
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1 /**
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2 * \page howto-ownership Howto: ownership and memory management
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3 * \tableofcontents
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4 *
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5 * How memory and ownership is used within Molko's Adventure API.
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6 *
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7 * # Synopsis
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8 *
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9 * In C, memory management can be a cumbersome issue and a major common complain
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10 * when it comes to leak.
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11 *
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12 * As such, the API itself does not use dynamic allocations in most of the case.
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13 * Instead it is kept to the user responsability to handle storage of data. In
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14 * that manner the code stays simpler, stronger and more flexible. The API
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15 * itself does not have to deal with memory management and deallocation, it only
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16 * expect data from user and work with that.
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17 *
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18 * You can imagine a situation with a DVD player and some movies on DVDs. You
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19 * have one DVD player where you put some DVDs inside but the DVD player never
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20 * make its own copy, it simply reads your disc and you get it back afterwards.
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21 *
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22 * Following this philosophy, the Molko's Adventure API for this scenario would
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23 * look like this:
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24 *
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25 * ```c
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26 * struct dvd_player player;
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27 * struct dvd dvd;
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28 *
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29 * dvd_open(&dvd, "/dev/sr0");
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30 *
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31 * dvd_player_turn_on();
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32 * dvd_player_insert(&player, &dvd);
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33 * dvd_player_play(&player);
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34 * dvd_player_turn_off();
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35 * ```
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36 *
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37 * # Memory handling
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38 *
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39 * ## Arrays
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40 *
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41 * Some modules in the API may require an array. Depending on the situation they
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42 * can be passed as parameter or are usually of a fixed reasonable size in
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43 * structures.
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44 *
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45 * They are always annotated with a macro to let the user flexibility over it if
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46 * necessary.
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47 *
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48 * Example, a player has a set of spells.
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49 *
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50 * ```c
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51 * #define PLAYER_SPELL_MAX (16)
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52 *
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53 * struct player {
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54 * struct spell *spells[PLAYER_SPELL_MAX];
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55 * };
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56 * ```
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57 *
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58 * ## Strings
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59 *
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60 * When dealing with strings, they are almost always referenced and not copied
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61 * unless explicitly required. As such, no allocation/deallocation required
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62 * either.
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63 *
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64 * ```c
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65 * struct player {
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66 * const char *name; // Not allocated, no deallocation
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67 * ```
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68 *
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69 * # Ownership
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70 *
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71 * Alongside the memory handling comes the ownership. Related to the DVD
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72 * scenario explained above, not having to *own* a resource within a structure
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73 * means no allocation/deallocation required.
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74 *
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75 * Also, since C does not have a scoped mechanism, all fields in structured are
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76 * publicly available and to avoid allocating them on the heap they are always
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77 * declared to the user even if they need internal data.
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78 *
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79 * As a documentation notice, fields are always annotated using (XYZ) prefix
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80 * with some symbols to indicate whether user is allowed to touch or not.
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81 *
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82 * The letter *X* defines the following restriction
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83 *
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84 * - `+`: The property is readable/editable by the user,
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85 * - `-`: The property is readable by the user,
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86 * - `*`: The property is not meant to be used directly by the user.
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87 *
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88 * The letter *Y* can be set to `&` in that case means it is only referenced
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89 * and is not an owned property (usually a non-owning pointer). Which means
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90 * user is responsible for deallocation if required.
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91 *
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92 * The finall letter *Z* can be set to `?` which means it is optional (like a
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93 * nullable pointer).
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94 *
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95 * Examples:
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96 *
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97 * ```c
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98 * struct foo {
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99 * int x; // (+) Position in x.
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100 * int y; // (+) Position in y.
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101 * struct theme *th; // (+&?) Theme to use.
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102 * unsigned int elapsed; // (-) Elapsed time since last frame.
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103 * struct texture text; // (*) Texture used for rendering.
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104 * };
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105 * ```
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106 *
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107 * Within this structure, the fields `x` and `y` are completely accessible to
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108 * the user for both reading/writing. The field `th` is an optional non-owning
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109 * pointer to a theme which is also readable/writable. The field `elapsed` is
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110 * readable but should not be modified. Finally, the field `text` is private
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111 * and should not be touched by the user.
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112 *
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113 * # Memory handling in Molko's Adventure API
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114 *
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115 * | | Dynamic allocation? | Notes |
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116 * |---------|---------------------|---------------------------------------------------------|
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117 * | libcore | None | The util.h provides convenient allocators for the user. |
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118 * | libui | None | |
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119 * | librpg | In map.h module | Maps are big chunk of data. |
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120 */