Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hplabs!hpl-opus!hpnmdla!darrylo
From: darrylo@hpnmdla.HP.COM (Darryl Okahata)
Newsgroups: comp.sys.hp
Subject: Re: Interrupted library calls
Message-ID: <430017@hpnmdla.HP.COM>
Date: 17 Jan 90 02:14:25 GMT
References: <373@node17.mecazh.UUCP>
Organization: HP Network Measurements Div, Santa Rosa, CA
Lines: 33

In comp.sys.hp, paul@mecazh.UUCP (Paul Breslaw) writes:

> This problem cropped up in the context of Xlib, but could equally apply to 
> any Unix library. Hence the posting to more than one group.
> 
> Our application (a CAM package on HP9000/3xx machines under HP-UX6.5 X11.R2)
> crashes sometimes when we handle a signal and return from 
> the signal handler in a different context from the one in which the handler 
> was entered. In other words we do a longjmp(3) from inside the handler.
> 
> We found that this is an elegant way to design certain features into a program.

[ You're not going to like this ... ]

     This was one of the problems discussed in comp.windows.x some time
back: you cannot interrupt (via a signal) an X-window library call (at
least this is true of X11R2 and, I believe, X11R3 -- I'm not sure about
X11R4, however).

     As this is a generic problem with X-windows (this is not an "HP"
problem), you have the following choices:

1. Don't use signals (even to just set a flag and return).
2. Temporarily block *ALL* signals during a X-window call.  This is, I
   believe, the approach taken by GNU Emacs.

     -- Darryl Okahata
	UUCP: {hplabs!, hpcea!, hpfcla!} hpnmd!darrylo
	Internet: darrylo%hpnmd@hpcea.HP.COM

DISCLAIMER: this message is the author's personal opinion and does not
constitute the support, opinion or policy of Hewlett-Packard or of the
little green men that have been following him all day.