SIGCHLD and the Starbase Input Daemon

The Starbase input daemon is started whenever tracking or event monitoring is enabled. When tracking and event monitoring are turned off or when the output device is closed, Starbase terminates the daemon, using this process:

1.Set the SIGCHLD action to SIG_DFL, saving the old action.

2.Send a message to the input daemon asking it to terminate.

3.Call waitpid(2) to wait for the daemon's death.

4.Restore the saved SIGCHLD action.

In a Starbase application using tracking or events, a non-graphics thread should not set the SIGCHLD action by calls to sigaction(2), sigvector(2), signal(2), sigset(2), or sigwait(2) concurrently with calls in the graphics thread to track(3g), track_off(3g), disable_events(3g), or gclose(3g).

Possible consequences of violating this restriction are the same as those listed above for the grmd daemon.

SIGPIPE Details

The graphics libraries start a daemon process and communicate with that process via sockets in two situations:

•For hardware texture mapping on an hp VISUALIZE-48/-48XP display using the Texture Interrupt Manager Daemon (timd).

•For hp-PHIGS input using the PHIGS daemon (phg_daemon).

When starting either of these daemons, the graphics library permanently sets the SIGPIPE action to SIG_IGN. This prevents the terminating SIGPIPE signal from being delivered to the process should the daemon die abnormally.

If your application changes the SIGPIPE action to SIG_DFL or to a specific handler, an abnormal death of either timd or phg_daemon will result in a SIGPIPE signal being delivered to the process when the graphics library next attempts to communicate with the daemon. If the action is SIG_DFL, the process will terminate.

Gamma Correction

Gamma correction is used to alter hardware colormaps to compensate for the non-linearities of CRT monitors. Gamma correction can be used to improve the "ropy" or modulated appearance of antialiased lines. Gamma correction is also used to improve the appearance of shaded graphics images as well as scanned photographic images that have not already been gamma corrected.

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Graphics Administration Guide for HP-UX 10.20