The Effects of Client Failures

The most common situation in which one PEXlib client can adversely affect another occurs when a client passes bad values in its data. This may cause a server to dump core, thus affecting all the clients connected to that server. However, the effects of this vary according the connection method of the PEXlib client — whether DHA, PEX, or X.

In the PEX method, a client can send bad floating-point data values to the PEX server, causing it to abort and affecting all other PEX clients. The HP PEX server supplies reasonable default values as results for operations involving bad data. The resulting images may not appear as you expected them, but the server will not fail. The effects of bad data on non-HP servers is unknown.

For clients using the X protocol method to render to a non-PEX-capable server, an abort will normally occur only on the client side — without affecting any other X or PEX clients. However, if for some reason the client aborts the X server itself, all other X/PEX clients also abort just as if any other X client aborts the X server.

Benefits gained by operating clients in the DHA protocol method are speed, isolation from other clients, and if a DHA client aborts, it is not likely to affect other PEXlib clients.

The following table describes the most common data values causing these problems and should be avoided:

It is important to know of these three conditions because many applications generate their graphics data as part of some application-specific calculations — and generated data is prone to producing these "toxic numbers." If this occurs, your displayed images can appear with unexpected results. To avoid this situation, your application must not generate these three conditions or must filter these conditions from their data.