RSC/MP Programming Manual

Application Design

Restrictions

Some elements of the RSC/MP library are not safe to use in a multithreaded

application:

The default options (selected by using RSC_DEFAULT_OPTIONS as an options

handle) are shared between all threads, regardless of thread registration. Any

thread using these options is affected by any change made from any other thread.

To avoid this condition, have each thread create and load its own options.

The ERROR_FILE option is global to all threads; separate threads cannot use

different error files.

Using TMF to Ensure Data Integrity

The Transaction Management Facility (TMF) helps to ensure data integrity. When

designing an application, consider these factors:

The type of data that is in the database and how to maintain the integrity of the

data.

If an error is encountered, whether the transaction should be ended (committed) or

aborted (rolled back).

Whether transactions are controlled explicitly or automatically.

Whether there are single or multiple transactions running, using waited or nowaited

I/O.

For further information about ensuring data integrity in an application, see Monitoring

Transaction Calls on page 6-6.

Waited and Nowaited I/O

RSC/MP allows waited or nowaited I/O when initiated through the RscWrite or

RscWriteRead function calls. Using waited I/O forces the application to wait until the

I/O operation completes before returning control to the application. Using nowaited I/O

allows the application to initiate the I/O and return control to the application

immediately; the application can then check periodically using the RscIoCheck function

to determine if the I/O has completed.

Nowaited I/O is slightly more complicated, requiring two API calls, while waited I/O

requires only one API call. Your choice of waited or nowaited I/O depends on the

needs of your application.

If an application requires multiple, outstanding, nowaited RscWriteRead function calls

to the same Guardian process server, the server replies to the WriteRead function calls

in the order they were received. Because the server must respond to the first call

before it responds to subsequent calls, this situation can result in poor performance of

the application.

HP NonStop Remote Server Call (RSC/MP) Programming Manual — 522360-006

5- 3