Notification of events

DESCRIPTION

Each application, that connects to a IOSYS-server can request event notification for certain objects and event types. Every time an event for such objects occures, all applications that requested the notification will be informed by the IOSYS-server. This is called data processing on event driven basis. You don't have to periodically read an object, only changes are transfered to all clients.
All clients, that connect to the server with the iosConnect command (and of course all PCC-supplied applications) build a event queue when connecting to the server. Each time a event for that applications occurs, it is appended to this queue. By using the commands iosEventsQueued and iosGetEvent the clients can query the queue or pop one entry from it. Events are processed on a first in first out basis.
All data, that is sent to the server, i.e. iosSetObject, iosCreateObject and iosDestroyObject, store their changes in a local data structure, before sending the data to the server. This output buffer is flushed either when it becomes full or an explicit flush with iosFlush is requested.

EVENT TYPES

The following types of events are known:

eventmask	occures when
change	value of object changes
access	any client starts/stops accessing this object
message	message has been sent
notify	object has been destroyed¹
config	object has been configured
alarm	alarm condition for object has come true

KEYWORDS

Copyright © 1999 Gerhard Hintermayer.