Notification

Notification feature. More...

Files
file	kdbnotification.h
	Elektra-Notification structures and declarations for application developers.
file	kdbnotificationinternal.h
	Elektra-Notification structures and declarations for developing notification and transport plugins.

Typedefs
typedef void(*	ElektraNotificationConversionErrorCallback) (Key *key, void *context)
	Callback function called when string to number conversion failed.
typedef void(*	ElektraNotificationChangeCallback) (Key *key, void *context)
	Callback function for key changes.

Functions
int	elektraNotificationOpen (KDB *kdb)
	Initialize the notification system for the given KDB instance.
int	elektraNotificationClose (KDB *kdb)
	Stop the notification system for the given KDB instance.
int	elektraNotificationRegisterCallback (KDB *kdb, Key *key, ElektraNotificationChangeCallback callback, void *context)
	Subscribe for updates via callback when a given key value is changed.
int	elektraNotificationRegisterCallbackSameOrBelow (KDB *kdb, Key *key, ElektraNotificationChangeCallback callback, void *context)
	Subscribe for updates via callback when a given key or a key below changed.
	ELEKTRA_NOTIFICATION_REGISTER_SIGNATURE (int, Int)
	Subscribe for automatic updates to a given variable when the given key value is changed.

Detailed Description

Notification feature.

For an introduction to notifications please see the Notification Tutorial.

Examples:

• Basic notifications using polling
• Using asynchronous I/O bindings
• Reload KDB when Elektra's configuration has changed

Global Mounting

elektraNotificationOpen() loads and mounts the internalnotification plugin globally at run-time. The key database is not altered permanently. elektraNotificationClose() reverts the mounting.

The internalnotification plugin is mounted at its defined positions (see its plugin docs).

• If there is no plugin mounted at a required position the internalnotification plugin is mounted at this position.
• In the default configuration or when mounting a plugin globally using kdb global-mount the list plugin is mounted at all positions. This plugin allows to mount multiple plugins at a position. If this plugin is present at a position the internalnotification plugin is added to the list plugin's configuration at run-time.
• If another plugin is mounted at a desired position the configuration is considered broken and mounting is aborted. The list plugin requires to be mounted at all positions in order to keep track of the current position and call plugins accordingly.

Transport Plugins

Notification transport plugins (or simply transport plugins) export "openNotification" (ElektraNotificationOpenNotification()) and optionally "closeNotification" (ElektraNotificationCloseNotification()) functions as part of their contract.

The function "openNotification" is called during elektraNotificationOpen(). At this point an I/O binding is set and it is save to use it. If no binding is set despite the plugin requires it, it should log a message and perform no additional operations. This ensures that the plugin can be used in applications that do not use I/O bindings or notification features.

ElektraNotificationOpenNotification() receives a callback and additional data. When a key change notification is received (or a change is detected by other means) this callback shall be called with the changed Key and the additional data.

Typedef Documentation

ElektraNotificationChangeCallback

typedef void(* ElektraNotificationChangeCallback) (Key *key, void *context)

Callback function for key changes.

Parameters

Key	changed key
context	user supplied callback context

ElektraNotificationConversionErrorCallback

typedef void(* ElektraNotificationConversionErrorCallback) (Key *key, void *context)

Callback function called when string to number conversion failed.

Parameters

Key	key with invalid value
context	user supplied callback context

Function Documentation

ELEKTRA_NOTIFICATION_REGISTER_SIGNATURE()

ELEKTRA_NOTIFICATION_REGISTER_SIGNATURE	(	int	,
		Int	)

Subscribe for automatic updates to a given variable when the given key value is changed.

On kdbGet iff the key is present and its content is valid, the registered variable is updated.

Parameters

handle	plugin handle
Key	key to watch for changes
variable	variable

Return values

1	on success
0	on failure

elektraNotificationClose()

int elektraNotificationClose

(

KDB *

kdb

)

Stop the notification system for the given KDB instance.

May only be called after elektraNotificationOpen() was called for given KDB instance.

Parameters

kdb	KDB instance

Return values

1	on success
0	on error

elektraNotificationOpen()

int elektraNotificationOpen

(

KDB *

kdb

)

Initialize the notification system for the given KDB instance.

Asynchronous receiving of notifications requires an I/O binding. Use elektraIoSetBinding() before calling this function.

May only be called once for a KDB instance. Subsequent calls return 0.

Parameters

kdb	KDB instance

Return values

1	on success
0	on error

elektraNotificationRegisterCallback()

int elektraNotificationRegisterCallback	(	KDB *	kdb,
		Key *	key,
		ElektraNotificationChangeCallback	callback,
		void *	context )

Subscribe for updates via callback when a given key value is changed.

Parameters

handle	plugin handle
Key	key to watch for changes
callback	callback function
context	user supplied context passed to callback function

Return values

1	on success
0	on failure

elektraNotificationRegisterCallbackSameOrBelow()

int elektraNotificationRegisterCallbackSameOrBelow	(	KDB *	kdb,
		Key *	key,
		ElektraNotificationChangeCallback	callback,
		void *	context )

Subscribe for updates via callback when a given key or a key below changed.

Parameters

handle	plugin handle
Key	key to watch for changes
callback	callback function
context	user supplied context passed to callback function

Return values

1	on success
0	on failure