SNAX/APC Application Programming Manual

Interprocess Communications and Units of Work

SNAX/APC Application Programming Manual—138786

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IPC Message Structure

TPs communicate with the SNAX/APC system through the Tandem file system using a

message-oriented application program interface. The basic unit of communication is an

interprocess communication or IPC message. The IPC messages flow in both

directions, both to and from SNAX/APC. Typically, as shown in Figure 2-1

, the TP

sends an IPC containing a verb request to SNAX/APC, and SNAX/APC replies with an

IPC containing return codes and other indications of what has been received.

SNAX/APC acts as the LU, assembles the requests from the TP and creates SNA

Request Units (RUs) which are sent to the Tandem SNA access method, SNAX/XF,

SNAX/APN or SNAX/APN-EN. The Tandem SNA access method sends these over the

network to the target LU. Incoming traffic received by the Tandem SNA access method

is passed up to SNAX/APC which decodes the SNA RUs into IPC messages to forward

on to the TP.

Units Of Work and Interprocess Communications

Each IPC message begins with an IPC header, which contains information about the

message. Following the header, an IPC message contains one or more SNAX/APC units

of work (UOWs).

A UOW is a structured message that identifies the operation requested and provides the

necessary information. For example, UOWs can be used to invoke a host application,

receive a message from the host, or confirm completion of a transaction. UOWs are

either verb request or reply UOWs.

All UOWs in an IPC message are checked for validity before any UOWs are processed.

Several UOWs can be concatenated into a single IPC message, thus reducing

interprocess traffic and improving performance within the system (see Figure 2-2

Figure 2-1. Communications Overview

012CDT .CDD

IPC Messages and Replies

SNA RUs

Transaction

Program

SNAX/APC

SNAX/XF or

SNAX/APN