Path: utzoo!utgpu!jarvis.csri.toronto.edu!smoke.cs.toronto.edu!neat.cs.toronto.edu!moraes
Newsgroups: comp.windows.x
From: moraes@cs.toronto.edu (Mark Moraes)
Subject: Re: X & signals
Message-ID: <90Feb25.153205est.380@smoke.cs.toronto.edu>
Keywords: Don't get fancy with signals
Organization: Department of Computer Science, University of Toronto
References: <1154@sdrc.UUCP>
Date: 25 Feb 90 20:32:35 GMT
Lines: 13

As has often been pointed out before (comp.lang.c, comp.std.c,
comp.std.unix) about the only thing one can do safely in a signal
handler is set a flag, and return, or cleanup and exit.  (Even the
latter may not be quite safe, but heck, you're exiting...) 

Calling any procedure or touching global data is perilous -- parts of
the C library are not reentrant (malloc for sure) and calling anything
that might call these parts might put your application into a very
confused state.  I don't know how much of Xlib or Xt is re-entrant, I
suspect there are non-re-entrant parts.  (Perhaps a scenario where
Xlib gets interrupted when packing data into a buffer, the signal
handler tries to pack more data into that buffer resulting in an
interleaved mess?)