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/*
Copyright (C) 2010-2011 David Robillard <http://drobilla.net>
Copyright (C) 2010 Leonard Ritter <paniq@paniq.org>
This header is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published
by the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This header is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this header; if not, write to the Free Software Foundation,
Inc., 59 Temple Place, Suite 330, Boston, MA 01222-1307 USA
*/
/**
@file
C API for the LV2 Persist extension <http://lv2plug.in/ns/ext/persist>.
*/
#ifndef LV2_PERSIST_H
#define LV2_PERSIST_H
#include <stdbool.h>
#include <stdint.h>
#ifdef __cplusplus
extern "C" {
#endif
#define LV2_PERSIST_URI "http://lv2plug.in/ns/ext/persist"
/**
A host-provided function to store a value under a given key.
@param callback_data Must be the callback_data passed to LV2_Persist.save().
@param key The key (predicate) to store @a value under (URI mapped integer).
@param value Pointer to the value (object) to be stored.
@param size The size of the data at @a value in bytes.
@param type The type of @a value (URI mapped integer).
@param pod True iff @a value is POD.
@return 0 on success, otherwise a non-zero error code.
The host passes a callback of this type to LV2_Persist.save().
This callback is called repeatedly by the plugin within
LV2_Persist.save() to store all the key/value records that describe
its current state.
If @a pod is true, @a value is guaranteed to be architecture-independent POD
(i.e. a region of memory that does not contain pointers or references to
non-persistent resources and can safely be copied and stored with a simple
memcpy). Note that this definition of POD is more strict than exclusively
in-memory definitions since the value MUST be architecture independent;
e.g. endianness must be considered (so basic numeric types are typically NOT
POD). Hosts MAY fail to store the value, particularly if it is
non-POD. Plugins MUST gracefully handle this situation, even though state
may not be fully restored. Hosts SHOULD support any POD value, even if the
host does not know anything about its type. Plugins SHOULD express their
state entirely with POD values whenever possible, and use non-POD values
only where necessary. Plugins SHOULD use common RDF types and/or types from
the Atom extension <http://lv2plug.in/ns/ext/atom> whenever possible since
hosts are likely to already contain the necessary implementation.
Note that @a size MUST be > 0, and @a value MUST point to a valid region of
memory @a size bytes long (this is required to make restore unambiguous).
The plugin MUST NOT attempt to use this function outside of the
LV2_Persist.restore() context.
*/
typedef int (*LV2_Persist_Store_Function)(
void* callback_data,
const uint32_t key,
const void* value,
size_t size,
uint32_t type,
bool pod);
/**
A host-provided function to retrieve a value under a given key.
@param callback_data Must be the callback_data passed to LV2_Persist.restore().
@param key The key (predicate) of the value to retrieve (URI mapped integer).
@param size (Output) If non-NULL, set to the size of the restored value.
@param type (Output) If non-NULL, set to the type of the restored value.
@param pod (Output) If non-NULL, set to true iff @a value is POD.
@return A pointer to the restored value (object), or NULL if no value
has been stored under @a key.
A callback of this type is passed by the host to LV2_Persist.restore(). This
callback is called repeatedly by the plugin within LV2_Persist.restore() to
retrieve the values of any keys it requires to restore its state.
The returned value MUST remain valid until LV2_Persist.restore() returns.
The plugin MUST NOT attempt to use this function, or any value returned from
it, outside of the LV2_Persist.restore() context. Returned values MAY be
copied for later use if necessary, assuming the plugin knows how to
correctly do so (e.g. the value is POD, or the plugin understands the type).
*/
typedef const void* (*LV2_Persist_Retrieve_Function)(
void* callback_data,
uint32_t key,
size_t* size,
uint32_t* type,
bool* pod);
/**
Persist Extension Data.
When the plugin's extension_data is called with argument LV2_PERSIST_URI,
the plugin MUST return an LV2_Persist structure, which remains valid for
the lifetime of the plugin.
The host can use the contained function pointers to save and restore the
state of a plugin instance at any time (provided the threading restrictions
for the given function are met).
The typical use case is to save the plugin's state when a project is
saved, and to restore the state when a project has been loaded. Other
uses are possible (e.g. cloning plugin instances or taking a snapshot
of plugin state).
Stored data is only guaranteed to be compatible between instances of plugins
with the same URI (i.e. if a change to a plugin would cause a fatal error
when restoring state saved by a previous version of that plugin, the plugin
URI MUST change just as it must when ports change incompatibly). Plugin
authors should consider this possibility, and always store sensible data
with meaningful types to avoid such compatibility issues in the future.
*/
typedef struct _LV2_Persist {
/**
Save plugin state using a host-provided @a store callback.
@param instance The instance handle of the plugin.
@param store The host-provided store callback.
@param callback_data An opaque pointer to host data, e.g. the map or
file where the values are to be stored. If @a store is called,
this MUST be passed as its callback_data parameter.
The plugin is expected to store everything necessary to completely
restore its state later (possibly much later, in a different
process, on a completely different machine, etc.)
The @a callback_data pointer and @a store function MUST NOT be
used beyond the scope of save().
This function has its own special threading class: it may not be
called concurrently with any "Instantiation" function, but it
may be called concurrently with functions in any other class,
unless the definition of that class prohibits it (e.g. it may
not be called concurrently with a "Discovery" function, but it
may be called concurrently with an "Audio" function. The plugin
is responsible for any locking or lock-free techniques necessary
to make this possible.
Note that in the simple case where state is only modified by
restore(), there are no synchronization issues since save() is
never called concurrently with restore() (though run() may read
it during a save).
Plugins that dynamically modify state while running, however,
must take care to do so in such a way that a concurrent call to
save() will save a consistent representation of plugin state for a
single instant in time.
*/
void (*save)(LV2_Handle instance,
LV2_Persist_Store_Function store,
void* callback_data);
/**
Restore plugin state using a host-provided @a retrieve callback.
@param instance The instance handle of the plugin.
@param retrieve The host-provided retrieve callback.
@param callback_data An opaque pointer to host data, e.g. the map or
file from which the values are to be restored. If @a retrieve is
called, this MUST be passed as its callback_data parameter.
The plugin MAY assume a restored value was set by a previous call to
LV2_Persist.save() by a plugin with the same URI.
The plugin MUST gracefully fall back to a default value when a
value can not be retrieved. This allows the host to reset the
plugin state with an empty map.
The @a callback_data pointer and @a store function MUST NOT be used
beyond the scope of restore().
This function is in the "Instantiation" threading class as defined
by LV2. This means it MUST NOT be called concurrently with any other
function on the same plugin instance.
*/
void (*restore)(LV2_Handle instance,
LV2_Persist_Retrieve_Function retrieve,
void* callback_data);
} LV2_Persist;
#ifdef __cplusplus
} /* extern "C" */
#endif
#endif /* LV2_PERSIST_H */
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