man nameserv::auto (3): Name service facility, Client Extension

SYNOPSIS

package require Tcl 8.4

package require nameserv::auto ?0.3?

package require nameserv

DESCRIPTION

Please read the document Name service facility, introduction first.

This package provides the exact same API as is provided by package nameserv, i.e. the regular name service client. It differs from the former by taking measures to ensure that longer-lived data, i.e. bound names, continuous and unfullfilled async searches, survive the loss of the connection to the name server as much as is possible.

This means that the bound names and continuous and unfullfilled async searches are remembered client-side and automatically re-entered into the server when the connection comes back after its loss. For bound names there is one important limitation to such restoration: It is possible that a name of this client was bound by a different client while the connection was gone. Such names are fully lost, and the best the package can and will do is to inform the user of this.

API

The user-visible API is mainly identical to the API of nameserv and is therefore not described here. Please read the documentation of nameserv.

The differences are explained below, in the sections OPTIONS and EVENTS.

OPTIONS

This package supports all the options of package nameserv, plus one more. The additional option allows the user to specify the time interval between attempts to restore a lost connection.

-delay milliseconds: The value of this option is an integer value > 0 which specifies the interval to wait between attempts to restore a lost connection, in milliseconds. The default value is 1000, i.e. one second.

EVENTS

This package generates all of the events of package nameserv, plus two more. Both events are generated for the tag nameserv.

lost-name: This event is generated when a bound name is truly lost, i.e. could not be restored after the temporary loss of the connection to the name server. It indicates that a different client took ownership of the name while this client was out of contact.
The detail information of the event will be a Tcl dictionary containing two keys, name, and data. Their values hold all the information about the lost name.
re-connection: This event is generated when the connection to the server is restored. The remembered data has been restored when the event is posted.
The event has no detail information.

DESIGN

The package is implemented on top of the regular nameservice client, i.e. package nameserv. It detects the loss of the connection by listening for lost-connection events, on the tag nameserv.

It reacts to such events by starting a periodic timer and trying to reconnect to the server whenver this timer triggers. On success the timer is canceled, a re-connection event generated, and the package proceeds to re-enter the remembered bound names and continuous searches.

Another loss of the connection, be it during or after re-entering the remembered information simply restarts the timer and subsequent reconnection attempts.

BUGS, IDEAS, FEEDBACK

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category nameserv of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also report any ideas for enhancements you may have for either package and/or documentation.

KEYWORDS

automatic, client, name service, reconnect, restore

COPYRIGHT

Copyright (c) 2007-2008 Andreas Kupries <[email protected]>