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:

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.