HEARTBEAT Messages
Introduction
Support for !HEARTBEAT-… messages is coded into the base Application class. It should not be necessary for any application to explicitly implement support for these messages.
The internal !HEARTBEAT-… messages are:
!HEARTBEAT-REQUEST!HEARTBEAT-RESPONSE
Note that these messages begin with the special ! character, and so are treated
as administration messages. They will be passed between applications using the
dedicated administration message FIFO mechanism, and will always be processed before
user-level messages are processed.
!HEARTBEAT-REQUEST
The !HEARTBEAT-REQUEST message is sent periodically by the WatchdogApp, assuming
that the heartbeat_interval_secs is configured to a non-zero value.
The attributes of the !HEARTBEAT-REQUEST message are:
Field
Type
Description
app_name
String
The name of the application to which the message is being sent.
heartbeat_num
Integer
A monotonically incrementing number to correlate heartbeat requests with responses.
!HEARTBEAT-RESPONSE
The !HEARTBEAT-RESPONSE message must be returned promptly by the receiving application.
The contents should be an exact echo of the received request message.
The attributes of the !HEARTBEAT-RESPONSE message are:
Field
Type
Description
app_name
String
The name of the application to which the message is being sent.
heartbeat_num
Integer
A monotonically incrementing number to correlate heartbeat requests with responses.