Open System Services Porting Guide (G06.24+, H06.03+)

Porting UNIX Applications to the OSS Environment
Open System Services Porting Guide—520573-006
7-5
HP Extensions
program for a loosely coupled, multiprocessor environment. As discussed in Section 6,
OSS Porting Considerations, significant performance improvements can be achieved
in redesigning a server to run as a super server. Each slave server runs as a persistent
process in a separate processor, thus avoiding process-creation and termination
overhead for each request handled by the server (super server).
HP Extensions
If you want the UNIX program being ported to the OSS environment to be portable
back to the UNIX environment, HP extensions to the standard functions and functions
specific to HP should be used only as a last resort. Some standard functions have
been extended to take advantage of the OSS environment and to access Guardian
objects. Additionally, functions have been added to provide OSS processes with
attributes found only in the Guardian environment.
Further, OSS application programs have access to many of the Guardian procedure
calls typically used by programs running in the Guardian environment. All of these HP
extensions are available to OSS applications.
Programming for Portability
There are general guidelines in making programs portable. One good programming
practice to make it easier to port your program to other environments is to use a
template that forces you to structure your source code in a modular way. This template
could consist of the elements described in You Should Use Portable Application
Templates on page 1-1, and further explained in Lewine’s POSIX Programmer’s Guide
(see Related Reading on page xv).
Other good guidelines to follow include:
•
Avoid machine dependencies in the manipulation of internal data structures. For
example, do not use multicharacter char constants or code that makes
assumptions about padding or byte order internal to structure elements. Refer to
Resolving the Endian Problem on page 9-8 for examples and more specific
guidelines about one such problem.
•
Define the formats of program data transfers within the program in a
hardware-independent way. (The actual transfers can take place through
intermediate disk files or through an interprocess-communication mechanism.)
•
Use a common subset of function calls, wherever possible.
•
When using a nonportable feature is essential, use a generic function which in turn
calls the nonportable function available under each of the operating system
environments supported. A library of machine-dependent features can be used to
create an operating system environment that is a superset of the target operating
system.
•
System-dependent features should be isolated into a machine-dependent module
that provides a common interface in all implementations.