1 /* lv2_persist.h - C header file for the LV2 Persist extension.
2 * Copyright (C) 2010 Leonard Ritter <paniq@paniq.org>
4 * This header is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU Lesser General Public License as published
6 * by the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This header is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
12 * License for more details.
14 * You should have received a copy of the GNU Lesser General Public License
15 * along with this header; if not, write to the Free Software Foundation,
16 * Inc., 59 Temple Place, Suite 330, Boston, MA 01222-1307 USA
20 * C header for the LV2 Persist extension <http://lv2plug.in/ns/ext/persist>.
30 #define LV2_PERSIST_URI "http://lv2plug.in/ns/ext/persist"
32 /** A host-provided function to store a value under a given key.
33 * @param callback_data Must be the callback_data passed to LV2_Persist.save().
34 * @param key The URI key (predicate) under which the value is to be stored.
35 * @param value Pointer to the value (object) to be stored.
36 * @param size The size of the data at @a value in bytes.
37 * @param type The type of @a value, as a URI mapped to an integer.
39 * The host passes a callback of this type to LV2_Persist.save(). This
40 * callback is called repeatedly by the plugin within LV2_Persist.save() to
41 * store all the key/value records that describe its current state.
43 * Unless @a type is 0, @a value is guaranteed to be POD (i.e. a region
44 * of memory that does not contain pointers and can safely be copied
45 * and persisted indefinitely with a simple memcpy). If @a type is 0,
46 * then @a value is a reference, as defined by the LV2 Atom extension
47 * <http://lv2plug.in/ns/ext/atom/>. Hosts are not required to support
48 * references: a plugin MUST NOT expect a host to persist references unless
49 * the host supports the feature <http://lv2plug.in/ns/ext/atom#blobSupport>.
50 * Plugins SHOULD express their state entirely with POD values.
52 * Note that @a size MUST be > 0, and @a value MUST point to a valid region of
53 * memory @a size bytes long (this is required to make restore unambiguous).
55 * The plugin MUST NOT attempt to use this function outside of the
56 * LV2_Persist.restore() context.
58 typedef void (*LV2_Persist_Store_Function)(
65 /** A host-provided function to retrieve a value under a given key.
66 * @param callback_data Must be the callback_data passed to LV2_Persist.restore().
67 * @param key The URI key (predicate) under which a value has been stored.
68 * @param size (Output) If non-NULL, set to the size of the restored value.
69 * @param type (Output) If non-NULL, set to the type of the restored value.
70 * @return A pointer to the restored value (object), or NULL if no value
71 * has been stored under @a key.
73 * A callback of this type is passed by the host to LV2_Persist.restore(). This
74 * callback is called repeatedly by the plugin within LV2_Persist.restore() to
75 * retrieve the values of any keys it requires to restore its state.
77 * The returned value MUST remain valid until LV2_Persist.restore() returns.
79 * The plugin MUST NOT attempt to use this function, or any value returned from
80 * it, outside of the LV2_Persist.restore() context. Returned values MAY be
81 * copied for later use if necessary.
83 typedef const void* (*LV2_Persist_Retrieve_Function)(
89 /** When the plugin's extension_data is called with argument LV2_PERSIST_URI,
90 * the plugin MUST return an LV2_Persist structure, which remains valid for
91 * the lifetime of the plugin.
93 * The host can use the contained function pointers to save and restore the
94 * state of a plugin instance at any time (provided the threading restrictions
95 * for the given function are met).
97 * The typical use case is to save the plugin's state when a project is
98 * saved, and to restore the state when a project has been loaded. Other
99 * uses are possible (e.g. cloning plugin instances or taking a snapshot
102 * Stored data is only guaranteed to be compatible between instances of plugins
103 * with the same URI (i.e. if a change to a plugin would cause a fatal error
104 * when restoring state saved by a previous version of that plugin, the plugin
105 * URI must change just as it must when a plugin's ports change). Plugin
106 * authors should consider this possibility, and always store sensible data
107 * with meaningful types to avoid such compatibility issues in the future.
109 typedef struct _LV2_Persist {
111 /** Save plugin state using a host-provided @a store callback.
113 * @param instance The instance handle of the plugin.
114 * @param store The host-provided store callback.
115 * @param callback_data An opaque pointer to host data, e.g. the map or
116 * file where the values are to be stored. If @a store is called,
117 * this MUST be passed as its callback_data parameter.
119 * The plugin is expected to store everything necessary to completely
120 * restore its state later (possibly much later, in a different
121 * process, on a completely different machine, etc.)
123 * The @a callback_data pointer and @a store function MUST NOT be
124 * used beyond the scope of save().
126 * This function has its own special threading class: it may not be
127 * called concurrently with any "Instantiation" function, but it
128 * may be called concurrently with functions in any other class,
129 * unless the definition of that class prohibits it (e.g. it may
130 * not be called concurrently with a "Discovery" function, but it
131 * may be called concurrently with an "Audio" function. The plugin
132 * is responsible for any locking or lock-free techniques necessary
133 * to make this possible.
135 * Note that in the simple case where state is only modified by
136 * restore(), there are no synchronization issues since save() is
137 * never called concurrently with restore() (though run() may read
140 * Plugins that dynamically modify state while running, however,
141 * must take care to do so in such a way that a concurrent call to
142 * save() will save a consistent representation of plugin state for a
143 * single instant in time. The simplest way to do this is to modify a
144 * copy of the state map and atomically swap a pointer to the entire
145 * map once the changes are complete (for very large state maps,
146 * a purely functional map data structure may be more appropriate
147 * since a complete copy is not necessary).
149 void (*save)(LV2_Handle instance,
150 LV2_Persist_Store_Function store,
151 void* callback_data);
153 /** Restore plugin state using a host-provided @a retrieve callback.
155 * @param instance The instance handle of the plugin.
156 * @param retrieve The host-provided retrieve callback.
157 * @param callback_data An opaque pointer to host data, e.g. the map or
158 * file from which the values are to be restored. If @a retrieve is
159 * called, this MUST be passed as its callback_data parameter.
161 * The plugin MAY assume a restored value was set by a previous call to
162 * LV2_Persist.save() by a plugin with the same URI.
164 * The plugin MUST gracefully fall back to a default value when a
165 * value can not be retrieved. This allows the host to reset the
166 * plugin state with an empty map.
168 * The @a callback_data pointer and @a store function MUST NOT be used
169 * beyond the scope of restore().
171 * This function is in the "Instantiation" threading class as defined
172 * by LV2. This means it MUST NOT be called concurrently with any other
173 * function on the same plugin instance.
175 void (*restore)(LV2_Handle instance,
176 LV2_Persist_Retrieve_Function retrieve,
177 void* callback_data);
185 #endif /* LV2_PERSIST_H */