Browse Prior Art Database

Logical Sequencing of Notification

IP.com Disclosure Number: IPCOM000102595D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 103K

Publishing Venue

IBM

Related People

Clark, CE: AUTHOR [+2]

Abstract

Events which occur on one system of a multisystem configuration must be reported to functions executing on all systems in the configuration. The underlying signalling mechanism between systems does not guarantee that signals are delivered in order. System services must insure notification of events occurs in a correct order and that this notification is not unduly delayed in the presence of unreliable systems or delays in signal delivery.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Logical Sequencing of Notification

       Events which occur on one system of a multisystem
configuration must be reported to functions executing on all systems
in the configuration.  The underlying signalling mechanism between
systems does not guarantee that signals are delivered in order.
System services must insure notification of events occurs in a
correct order and that this notification is not unduly delayed in the
presence of unreliable systems or delays in signal delivery.

      A protocol is described whereby notification is provided in a
logical order.  A time stamp is utilized to allow the system service
to determine the order of event occurrence.  The underlying premise
is that events must be reported as quickly as possible and that
events which arrive out of order need not be presented.

      The concept of logical ordering of events enables the system
service to deliver notification as soon as a signal arrives.  In so
doing, the most timely notification of events is achieved.
Additionally, the complexity and error prone nature of attempting to
insure ordered delivery of all events is eliminated.

      Notification of events will be performed by a system service
called "group notification".  Group notification will perform
notification to programs on the same system on which it is called as
well as every other system in the configuration.  This will be
accomplished by group notification sending a signal to every other
system in the configuration using a signalling service.  The
signalling service does not enforce ordered delivery of signals.
Systems which receive such signals will provide notification of the
event to other interested programs.

      Logical sequencing of events will be accomplished by defining
sets of related events which must be presented in order.  Events will
be ordered by a time stamp obtained when group notification is called
to process the event on the originating system.  On other systems in
the configuration, a signal will be received indicating an event has
occurred. If an event which has a time stamp earlier than a related
event, it will be discarded.  For example, if a JOIN event (which
will have an earlier time stamp) arrives after notification of a
QUIESCE event (which will have a later time stamp) has been
processed, the JOIN event will be discarded.

      The set of events supported by group notification and their
relationships are shown in the following table:
Event Type                    Event - meaning
Group Services      JOIN - program becomes active
                     LEAVE - normal program termination
                     QUIESCE - program enters a dormant state
                     DELETE - dormant or failed program deleted
FAILED - abnormal program termination detected
Temporary           PAUSE - temporary program outage reported or
           ...