SNAX/APC Application Programming Manual

Interprocess Communications and Units of Work

SNAX/APC Application Programming Manual—138786

2-11

Structure of the UOW Headers

User transaction programs (TPs) interact with SNAX/APC through verb requests and

replies. These verb requests and replies are in the form of Units of Work (UOWs),

which implement the functions described in the following subsection. IPC messages can

contain multiple UOWs (provided that all of the UOWs are intended for the same

conversation). All UOWs in an IPC message must be word-aligned.

Concatenation of several related UOWs into a single IPC message reduces interprocess

traffic and potentially enhances SNAX/APC performance characteristics. For example,

the LU 6.2 verbs ALLOCATE, SEND-DATA, and RECEIVE-AND-WAIT could be

concatenated into a single IPC message to SNAX/APC. The UOWs are processed in

their order of appearance in the IPC message.

Before processing any UOWs in an IPC message, SNAX/APC scans all the UOWs and

checks for invalid UOW headers. If SNAX/APC finds an invalid UOW header, it rejects

the entire IPC message. No UOWs in the IPC message are processed.

UOW Classes

SNAX/APC UOWs can be separated into three categories: service UOWs, control

operator verb UOWs, and conversational verb UOWs.

Service UOWs

Service UOWs provide initialization, reset, and dispatching functions among the

components of SNAX/APC. The five service UOWs are specific to SNAX/APC and are

not part of the SNA-defined LU 6.2 functions. The service UOWs are as follows:

DISPLAY-STATUS

This obtains information about local LUs (single-session only) controlled by that

SNAX/APC process. The information obtained includes session and conversation

information, the current verb on an active conversation, and pacing information.

DISPATCH-TP

This is sent by the Dispatcher to a local TP to inform the local TP of a request for a

conversation from a remote TP. This UOW contains information about the remote

TP that requested the services of the local TP. If an available copy of the local TP

does not exist, the PATHMON process creates an instance of the TP before sending

this UOW.

DISPATCHER-READY

This is sent by the Dispatcher to SNAX/APC when the Dispatcher is first

initialized. This UOW indicates to SNAX/APC that a Dispatcher is available to

create a TP, if necessary.

TP-READY

This initiates communication with the local SNAX/APC process and a local LU,

thus establishing a TP instance.