Volume 6A: Motif Programming Manual

This discussion is merely presented as an overview, since the implementation details are beyond the scope of this

book. For example, UNIX signals cause problems in a number of ways. The parent process is sent signals when the

child dies or its process state changes. The child is also sent signals that are delivered to the parent by the user or other

outside forces. Different forms of UNIX require that process groups be set up in different ways to avoid other

problems with signals.

Another problem involves file descriptors that are set up as non−blocking files. If read() returns 0 with one of these

descriptors, you may not know whether there is nothing to read or the end of the file has been reached, which means

that the child process has terminated. Incidentally, popen() does not deal with any of these issues correctly, so

building a new solution is the best thing to do in the long run.

You should really consult the programmer's guide for your UNIX system for more information on the techniques used

to spawn new processes and communicate with them appropriately. Once you have a handle on those issues, it should

be relatively easy to redirect text from file descriptors using the toolkit. For more information on

XtAppAddInput(), including examples of how it can be used, see Volume Four, X Toolkit Intrinsics

Programming Manual.

22.3 Dynamic Message Symbols

The MessageDialog is used to display many different types of messages; the image in the dialog helps the user

identify the purpose of the dialog. ...