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Message-ID:	<3D46AA34.1060609@hekimian.com>
Date:	Tue, 30 Jul 2002 11:01:08 -0400
X-Sybari-Trust:	e387bc9f b923d9bf 0879ee9b 00000109
From:	Joe Buehler <jbuehler AT hekimian DOT com>
Reply-To:	joseph DOT buehler AT spirentcom DOT com
Organization:	Spirent Communications
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CC:	Cygwin Developers <cygwin-developers AT cygwin DOT com>
Subject:	gcc problem with static instance destructors
References:	<3D46828F DOT 6090802 AT hekimian DOT com>

Looking at the code generated by gcc, it looks like it generates
code that is not thread-safe in a certain case.

It appears that static instances inside functions cause gcc
to generate a call to atexit() to call the destructor at
program exit time.

Compile the following and look at the assembly generated by
gcc:

struct x {
   int i;
   x() {
     i = 0;
   }
   ~x() {
     i = -1;
   }
};

int
main()
{
   static x temp;
   return(temp.i);
}

- The code that is generated to call atexit() does not look thread-safe.
   (handling of the flag variable that is tested to prevent duplicate calls)

- In addition, atexit() itself is not thread-safe.

So it looks like functions in cygwin that have internal static class instances
could be a serious source of problems.

This is using gcc-2.95.3-5.

Joe Buehler

- Raw text -