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Overview 5-3

21 Dec 2001

Overview

Asynchronous Support Layer library works as a filter between

existing ACI libraries (version 3 or later) and the client

application, which wants to issue asynchronous ACI calls.

Since the native ACI interface is synchronous, a client had to

wait for the completion of the request. Now using special

programming techniques, developers who want to use ACI in

an asynchronous manner can use the Asynchronous Support

Layer library of this purpose.

How It Works

In early ACI releases, all programmers using the ACI library,

had to consider that any ACI call issued by the application

would wait until the work is complete. Now, each incoming

request is stored into the shared memory area and each

request is executed in forked process.

After the application issues a request, it is given a request ID.

The request ID is actually the process ID of the forked child

process. The operating system does not allow two processes

with the same ID. The request ID ensures the uniqueness of

each ID.

After the request is completed, it stores the results in the

appropriate location in that shared table and terminates. To

retrieve the information back to the client, define a special

function that terminates (SIGCHLD) a child process. This

routine could also transmit the data into an application

internal data buffer and free the entry in the table. Doing this

ensures that the entry (process) ID will never be repeated in

the shared memory table.

Sadmin Sample Application

For the convenience and ease of understanding the

programming techniques required to write the asynchronous

ACI applications, the sadmin sample application is provided.

This application represents a cut version of the standard

dasadmin application. It the following commands:

•mount: mount a volser

• dismount: dismount the volser or force the drive to

dismount

• insert: insert volsers

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Adic Server Manuel d'utilisateur Page 175