Introduction to Pathmaker

Overview of Pathway
Introduction to Pathmaker and Pathway
1–16 067867 Tandem Computers Incorporated
Communication With IPC
Messages
Requesters and servers (and the services the servers contain) communicate with each
other through interprocess communication messages (commonly referred to as IPCs).
There are two types of IPC messages: request and reply.
Request Messages
Request messages are sent from a requester and received by a particular service. When
an end user presses a function key on the keyboard, the requester formats a message
that identifies the service (the business task) associated with that function key, along
with the data needed by the service to do its work. For example, if F4 is used to list a
vehicle by vehicle ID number, the associated request message will identify the List By
Vehicle ID Service and will contain the vehicle ID number the end user entered on the
screen.
A request message is initiated in the SCREEN COBOL requester code with the SEND
statement. Pathway then routes the request to a server containing the service. The
server reads the message from a special file called $RECEIVE and the appropriate
service carries out the request.
Reply Messages
Reply messages are formatted by a service and sent back to a requester after the service
has completed its work. A reply message is written to the $RECEIVE file in the server
code. Pathway then handles the routing of the reply message back to the appropriate
requester.
The message will contain one of the following:
Confirmation that the request was successful and the information that was
requested, if any
An error message if the request could not be fulfilled
The reply message can also contain logging and status information if application
logging or performance measurement is being done.
Note The Pathmaker product generates code to handle the routing of all IPC messages for an application.