Sigalrm Details - HP b2600 Administration Manual

Other Threads-Related Information
1. All of the 3D graphics functions are cancellation points.
2. None of the 3D graphics functions are async-cancel safe.
3. None of the 3D graphics functions are async-signal safe.
4. None of the 3D graphics functions are fork-safe, i.e., they cannot be called by a child process
after a fork(2), but before an exec(2).
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Note: Calls to 3D graphics functions between a fork and an exec have never been supported.
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5. There is one situation in which graphics behavior may be different for multi-threaded versus
single-threaded programs. In a multi-threaded Starbase application, a call to gopen(3g) a
serial plotter might not return if the plotter does not respond (e.g., if the plotter is turned off).
In this multi-threaded case, the graphics thread could wait forever for the device. Single-
threaded behavior in this case is for the gopen(3g) to timeout and return an error.

SIGALRM Details

The Starbase library temporarily sets a SIGALRM signal handler and uses setitimer(2) to start a timer in
two situations:
1. To set a timeout for device access in calls to gopen(3g) for a serial plotter.
2. To set a maximum time to wait for an event in calls to await_event(3g),
read_choice_event(3g), read_locator_event(3g), and intread_locator_event(3g).
Calls to the above Starbase functions should not be made in one thread while at the same
time another thread performs any of the following:
• Changes the SIGALRM signal action;
• Calls sigwait(2), selecting the SIGALRM signal;
• Uses setitimer(2);
• Uses timer_settime(2) to set a timer which will generate a SIGALRM signal.
Possible consequences of violating these non-concurrency restrictions are:
• The Starbase function call never returns;
• The wait for a plotter response or for an event is shorter than it should be;
• Alarm signals from timers set in other threads do not have the desired effect (because
the graphics signal handler is in place);
• Unpredictable results due to concurrent use of the process-wide timer provided by
setitimer(2).
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Graphics Administration Guide for HP-UX 10.20