SNAX/APC Application Programming Manual

Interprocess Communications and Units of Work

SNAX/APC Application Programming Manual—138786

2-3

IPC Message Structure

For example, a single IPC message might contain the UOWs ALLOCATE, SEND-

DATA, SEND-DATA, and CONFIRM. In this example, these four UOWs are issued and

completed in a single WRITEREAD procedure call.

Although you have the ability to enclose multiple UOWs in a single IPC message, you

should nevertheless be careful in your choice of UOWs. For example, including a

DEALLOCATE in the same UOW as an (MC)RECEIVE-AND-WAIT would cause

unexpected results. If SNAX/APC continues to process DEALLOCATE after

(MC)RECEIVE-AND-WAIT completes with a return code of 1005 (DEALLOCATE

NORMAL), SNAX/APC might have trouble in formatting an IPC reply because control

blocks have been released. Although it is possible to include more than one

(MC)RECEIVE-AND-WAIT in an IPC, you are advised to check the return code and

the WHAT-RECEIVED field before issuing the next verb request. This implies that if a

(MC)RECEIVE-AND-WAIT exists in the IPC, it should be the last UOW in that IPC

message.

UOWs consist of requests sent to SNAX/APC or replies from SNAX/APC (see

Figure 2-3

). The request consists of a header and a verb (mapped or basic) plus that

verb’s parameters. The reply consists of a header, verb code, and a return code from

SNAX/APC. Return code details may also be included.

TPs written in TAL or C communicate with SNAX/APC using the WRITEREAD

procedure. The WRITE portion of the WRITEREAD contains a request to SNAX/APC,

and the READ portion contains the reply for the requested operation.

TPs written in COBOL communicate with SNAX/APC using the READ statement with

the WITH PROMPT phrase. The prompt string contains the verb request; the

destination variable contains the reply.

TPs written in SCREEN COBOL communicate with SNAX/APC using the SEND

statement or the SEND MESSAGE statement, both of which have an implicit reply.

Figure 2-2. IPC Message Structure

Figure 2-3. UOW Structures

013CDT .CDD

IPC

Header

UOW UOW UOW

014CDT .CDD

UOW ID

Verb Code

Return

Code

RC Detail

Request

UOW ID

Verb Code Parm 1 Parm 2

• • •• • •