From:	"Chris Jones" <chris AT mynos DOT freeserve DOT co DOT uk>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Possible bug in Allegro 3.1
Date:	Sat, 9 Jan 1999 15:49:53 -0000
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

Having just upgraded from Allegro 3.0 to 3.1, I re-compiled a program which
uses it. The program was still a bit buggy - it used to occasionally cause
SIGSEGVs and the like. Since upgrading to 3.1, it now just crashes with
'Shutting down Allegro' repeatedly printing on the screen.
I investigated this, and found that my program was calling allegro_init()
twice by accident. This was not a problem with Allegro 3.0, but it seems
that 3.1's allegro_init() saves the old signal handlers to call when a fault
occurs (which, of course, on the second call to allegro_init() are its own
handlers). Therefore on a SIGSEGV it calls its own handler recursively, and
never exits.

For example, compiling this program under 3.1 will hang the system:
int main() {
  int zero,cause_fault;
  allegro_init();
  allegro_init();
  zero=0;
  cause_fault = 5 / zero;
  }

The strange thing is, that Allegro maintains the _allegro_count variable
with how many times allegro_init() has been called. So, a simple fix for
this would be to only call the signal-setting calls in allegro_init() if
_allegro_count is 0.

I know this is a very minor bug, and that people shouldn't call
allegro_init() twice anyway, but it can be frustrating to find what's wrong
with the program.

Chris Jones
-------------------------------
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