62 Chapter 4
Programming Guide
6. Other Tasks
6. Other Tasks
Other items to consider in developing A/P applications include:
• File descriptors
• Signal handling
• Error checking
File Descriptors
Communication endpoints for ACSE/Presentation applications are
HP-UX file descriptors. Because of unpredictable results, HP
recommends you do not use HP-UX file system calls such as exec(2),
dup(2), read(2), write(2), ioctl(2), or select(2) with HP OTS/9000 A
CSE/Presentation file descriptors. Note that fork(2) can be used, but do
not use fork(2) with exec(2).
A communication endpoint is returned when the ACSE/Presentation call
ap_open() is invoked.
Note that the user may need to increase the open file limit for the
application process to support a large number of connections. Refer to
the getrlimit() and setrlimit() system call manpages for more information
on changing file limits.
Signal Handlers
ACSE/Presentation calls interrupted by the arrival of a signal will not be
restarted by the library. You are responsible for managing signals and
providing recovery routines for the duration of any ACSE/Presentation
calls. Signals are interrupts such as when you enter ˆC on a terminal to
exit from a program.
If an interrupt occurs while executing A/P functions, the operating
system class error EINTR is returned. When detected, you must
re-invoke the A/P function. If EINTR is detected while executing
ap_snd() or ap_rcv(), the call must be invoked again as described in how
to handle AP_AGAIN in the ap_snd() and ap_rcv() manpages (for both
synchronous and asynchronous processing). The A/P library continues
the call from where it left off.
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