PeasEngine

## PeasEngine PeasEngine — Engine at the heart of the Peas plugin system. |

## Synopsis

    struct              PeasEngine;
    struct              PeasEngineClass;
    PeasEngine *        peas_engine_new                     (void);
    PeasEngine *        peas_engine_get_default             (void);
    void                peas_engine_add_search_path         (PeasEngine *engine,
                                                             const gchar *module_dir,
                                                             const gchar *data_dir);
    void                peas_engine_enable_loader           (PeasEngine *engine,
                                                             const gchar *loader_id);
    void                peas_engine_rescan_plugins          (PeasEngine *engine);
    const GList *       peas_engine_get_plugin_list         (PeasEngine *engine);
    gchar **            peas_engine_get_loaded_plugins      (PeasEngine *engine);
    void                peas_engine_set_loaded_plugins      (PeasEngine *engine,
                                                             const gchar **plugin_names);
    PeasPluginInfo *    peas_engine_get_plugin_info         (PeasEngine *engine,
                                                             const gchar *plugin_name);
    gboolean            peas_engine_load_plugin             (PeasEngine *engine,
                                                             PeasPluginInfo *info);
    gboolean            peas_engine_unload_plugin           (PeasEngine *engine,
                                                             PeasPluginInfo *info);
    void                peas_engine_garbage_collect         (PeasEngine *engine);
    gboolean            peas_engine_provides_extension      (PeasEngine *engine,
                                                             PeasPluginInfo *info,
                                                             GType extension_type);
    PeasExtension *     peas_engine_create_extension        (PeasEngine *engine,
                                                             PeasPluginInfo *info,
                                                             GType extension_type,
                                                             const gchar *first_property,
                                                             ...);
    PeasExtension *     peas_engine_create_extensionv       (PeasEngine *engine,
                                                             PeasPluginInfo *info,
                                                             GType extension_type,
                                                             guint n_parameters,
                                                             GParameter *parameters);
    PeasExtension *     peas_engine_create_extension_valist (PeasEngine *engine,
                                                             PeasPluginInfo *info,
                                                             GType extension_type,
                                                             const gchar *first_property,
                                                             va_list var_args);

## Object Hierarchy

      GObject
       +----PeasEngine

## Properties

      "loaded-plugins"           GStrv                 : Read / Write
      "plugin-list"              gpointer              : Read

## Signals

      "load-plugin"                                    : Run Last
      "unload-plugin"                                  : Run Last

## Description

The PeasEngine is the object which manages the plugins.

Its role is twofold:

- it will fetch all the information about the available plugins from all the registered plugin directories;

- it will provide you an API to load, control and unload your plugins and their extensions from within your application.

## Details

### struct PeasEngine

    struct PeasEngine;

The PeasEngine structure contains only private data and should only be accessed using the provided API.

### struct PeasEngineClass

    struct PeasEngineClass {
      GObjectClass parent_class;

      void     (*load_plugin)                 (PeasEngine     *engine,
                                               PeasPluginInfo *info);

      void     (*unload_plugin)               (PeasEngine     *engine,
                                               PeasPluginInfo *info);
    };

Class structure for PeasEngine.

GObjectClass `parent_class`; | The parent class.
`load_plugin` () | Signal class handler for the "load-plugin" signal.
`unload_plugin` () | Signal class handler for the "unload-plugin" signal.

### peas_engine_new ()

    PeasEngine *        peas_engine_new                     (void);

Return a new instance of PeasEngine. If no default PeasEngine has been instantiated yet, the first call of this function will set the default engine as the new instance of PeasEngine.

Returns : | a new instance of PeasEngine.

### peas_engine_get_default ()

    PeasEngine *        peas_engine_get_default             (void);

Return the existing instance of PeasEngine or a subclass of it. If no PeasEngine subclass has been instantiated yet, the first call of this function will return a new instance of PeasEngine.

Returns : | the existing instance of PeasEngine. [transfer none]

### peas_engine_add_search_path ()

    void                peas_engine_add_search_path         (PeasEngine *engine,
                                                             const gchar *module_dir,
                                                             const gchar *data_dir);

This function appends a search path to the list of paths where to look for plugins.

A so-called "search path" actually consists of both a module directory (where the shared libraries or language modules lie) and a data directory (where the plugin data is).

The plugin will be able to use a correct data dir depending on where it is installed, hence allowing to keep the plugin agnostic when it comes to installation location: the same plugin can be installed either in the system path or in the user's home directory, without taking other special care than using `peas_plugin_info_get_data_dir()` when looking for its data files.

If `data_dir` is `NULL`, then it is set to the same value as `module_dir`.

`engine` : | A PeasEngine.
`module_dir` : | the plugin module directory.
`data_dir` : | the plugin data directory. [allow-none]

### peas_engine_enable_loader ()

    void                peas_engine_enable_loader           (PeasEngine *engine,
                                                             const gchar *loader_id);

Enable a loader, enables a loader for plugins. The C plugin loader is always enabled.

For instance, the following code will enable python plugin from being loaded:

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    peas_engine_enable_loader (engine, "python");

Note: plugin loaders are shared across PeasEngines so enabling a loader on one PeasEngine will enable it on all PeasEngines.

`engine` : | A PeasEngine.
`loader_id` : | The id of the loader to enable.

### peas_engine_rescan_plugins ()

    void                peas_engine_rescan_plugins          (PeasEngine *engine);

Rescan all the registered directories to find new or updated plugins.

Calling this function will make the newly installed plugin infos be loaded by the engine, so the new plugins can be used without restarting the application.

`engine` : | A PeasEngine.

### peas_engine_get_plugin_list ()

    const GList *       peas_engine_get_plugin_list         (PeasEngine *engine);

Returns the list of PeasPluginInfo known to the engine.

`engine` : | A PeasEngine.
Returns : | a GList of PeasPluginInfo. Note that the list belongs to the engine and should not be freed. [transfer none][element-type Peas.PluginInfo]

### peas_engine_get_loaded_plugins ()

    gchar **            peas_engine_get_loaded_plugins      (PeasEngine *engine);

Returns the list of the names of all the loaded plugins, or an array containing a single `NULL` element if there is no plugin currently loaded.

Please note that the returned array is a newly allocated one: you will need to free it using `g_strfreev()`.

`engine` : | A PeasEngine.
Returns : | A newly-allocated `NULL`-terminated array of strings. [transfer full][array zero-terminated=1]

### peas_engine_set_loaded_plugins ()

    void                peas_engine_set_loaded_plugins      (PeasEngine *engine,
                                                             const gchar **plugin_names);

Sets the list of loaded plugins for `engine`. When this function is called, the PeasEngine will load all the plugins whose names are in `plugin_names`, and ensures all other active plugins are unloaded.

If `plugin_names` is `NULL`, all plugins will be unloaded.

`engine` : | A PeasEngine.
`plugin_names` : | A `NULL`-terminated array of plugin names, or `NULL`. [allow-none][array zero-terminated=1]

### peas_engine_get_plugin_info ()

    PeasPluginInfo *    peas_engine_get_plugin_info         (PeasEngine *engine,
                                                             const gchar *plugin_name);

Gets the PeasPluginInfo corresponding with `plugin_name`, or `NULL` if `plugin_name` was not found.

`engine` : | A PeasEngine.
`plugin_name` : | A plugin name.
Returns : | the PeasPluginInfo corresponding with a given plugin module name. [transfer none]

### peas_engine_load_plugin ()

    gboolean            peas_engine_load_plugin             (PeasEngine *engine,
                                                             PeasPluginInfo *info);

Loads the plugin corresponding to `info` if it's not currently loaded. Emits the "load-plugin" signal; loading the plugin actually occurs in the default signal handler.

`engine` : | A PeasEngine.
`info` : | A PeasPluginInfo.
Returns : | whether the plugin has been successfully loaded.

### peas_engine_unload_plugin ()

    gboolean            peas_engine_unload_plugin           (PeasEngine *engine,
                                                             PeasPluginInfo *info);

Unloads the plugin corresponding to `info`. Emits the "unload-plugin" signal; unloading the plugin actually occurs in the default signal handler.

`engine` : | A PeasEngine.
`info` : | A PeasPluginInfo.
Returns : | whether the plugin has been successfully unloaded.

### peas_engine_garbage_collect ()

    void                peas_engine_garbage_collect         (PeasEngine *engine);

This function triggers garbage collection on all the loaders currently owned by the PeasEngine. This can be used to force the loaders to destroy managed objects that still hold references to objects that are about to disappear.

`engine` : | A PeasEngine.

### peas_engine_provides_extension ()

    gboolean            peas_engine_provides_extension      (PeasEngine *engine,
                                                             PeasPluginInfo *info,
                                                             GType extension_type);

Returns if `info` provides an extension for `extension_type`. If the `info` is not loaded than `FALSE` will always be returned.

`engine` : | A PeasEngine.
`info` : | A PeasPluginInfo.
`extension_type` : | The extension GType.
Returns : | if `info` provides an extension for `extension_type`.

### peas_engine_create_extension ()

    PeasExtension *     peas_engine_create_extension        (PeasEngine *engine,
                                                             PeasPluginInfo *info,
                                                             GType extension_type,
                                                             const gchar *first_property,
                                                             ...);

If the plugin identified by `info` implements the `extension_type` interface, then this function will return a new instance of this implementation, wrapped in a new PeasExtension instance. Otherwise, it will return `NULL`.

When creating the new instance of the `extension_type` subtype, the provided construct properties will be passed to the extension construction handler (exactly like if you had called `g_object_new()` yourself).

The new extension instance produced by this function will always be returned wrapped in a PeasExtension proxy, following the current libpeas principle of never giving you the actual object (also because it might as well *not* be an actual object).

`engine` : | A PeasEngine.
`info` : | A loaded PeasPluginInfo.
`extension_type` : | The implemented extension GType.
`first_property` : | the name of the first property.
`...` : | the value of the first property, followed optionally by more name/value pairs, followed by `NULL`.
Returns : | a new instance of PeasExtension wrapping the `extension_type` instance, or `NULL`.

### peas_engine_create_extensionv ()

    PeasExtension *     peas_engine_create_extensionv       (PeasEngine *engine,
                                                             PeasPluginInfo *info,
                                                             GType extension_type,
                                                             guint n_parameters,
                                                             GParameter *parameters);

If the plugin identified by `info` implements the `extension_type` interface, then this function will return a new instance of this implementation, wrapped in a new PeasExtension instance. Otherwise, it will return `NULL`.

See `peas_engine_create_extension()` for more information.

`engine` : | A PeasEngine.
`info` : | A loaded PeasPluginInfo.
`extension_type` : | The implemented extension GType.
`n_parameters` : | the length of the `parameters` array.
`parameters` : | an array of GParameter. [allow-none][array length=n_parameters]
Returns : | a new instance of PeasExtension wrapping the `extension_type` instance, or `NULL`. Rename to: peas_engine_create_extension. [transfer full]

### peas_engine_create_extension_valist ()

    PeasExtension *     peas_engine_create_extension_valist (PeasEngine *engine,
                                                             PeasPluginInfo *info,
                                                             GType extension_type,
                                                             const gchar *first_property,
                                                             va_list var_args);

If the plugin identified by `info` implements the `extension_type` interface, then this function will return a new instance of this implementation, wrapped in a new PeasExtension instance. Otherwise, it will return `NULL`.

See `peas_engine_create_extension()` for more information.

`engine` : | A PeasEngine.
`info` : | A loaded PeasPluginInfo.
`extension_type` : | The implemented extension GType.
`first_property` : | the name of the first property.
`var_args` : | the value of the first property, followed optionally by more name/value pairs, followed by `NULL`.
Returns : | a new instance of PeasExtension wrapping the `extension_type` instance, or `NULL`.

## Property Details

### The `"loaded-plugins"` property

      "loaded-plugins"           GStrv                 : Read / Write

The list of loaded plugins.

This will be modified when `peas_engine_load_plugin()` or `peas_engine_unload_plugin()` is called.

This can be used with GSettings to save the loaded plugins by binding to this property after instantiating the engine by doing:

    1
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    4
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    g_settings_bind (gsettings_object,
                     LOADED_PLUGINS_KEY,
                     engine,
                     "loaded-plugins",
                     G_SETTINGS_BIND_DEFAULT);

Note: notify will not be called when the engine is being destroyed.

### The `"plugin-list"` property

      "plugin-list"              gpointer              : Read

The list of found plugins.

This will be modified when `peas_engine_rescan_plugins()` is called.

Note that the list belongs to the engine and should not be modified or freed.

## Signal Details

### The `"load-plugin"` signal

    void                user_function                      (PeasEngine     *engine,
                                                            PeasPluginInfo *info,
                                                            gpointer        user_data)      : Run Last

The load-plugin signal is emitted when a plugin is being loaded.

The plugin is being loaded in the default handler. Hence, if you want to perform some action before the plugin is loaded, you should use `g_signal_connect()`, but if you want to perform some action *after* the plugin is loaded (the most common case), you should use `g_signal_connect_after()`.

`engine` : | A PeasEngine.
`info` : | A PeasPluginInfo.
`user_data` : | user data set when the signal handler was connected.

### The `"unload-plugin"` signal

    void                user_function                      (PeasEngine     *engine,
                                                            PeasPluginInfo *info,
                                                            gpointer        user_data)      : Run Last

The unload-plugin signal is emitted when a plugin is being unloaded.

The plugin is being unloaded in the default handler. Hence, if you want to perform some action before the plugin is unloaded (the most common case), you should use `g_signal_connect()`, but if you want to perform some action after the plugin is unloaded (the most common case), you should use `g_signal_connect_after()`.

`engine` : | A PeasEngine.
`info` : | A PeasPluginInfo.
`user_data` : | user data set when the signal handler was connected.

## See Also

PeasPluginInfo