Set thread-local sig_atomic_t in signal handler?

Ian Lance Taylor
Thu Sep 26 16:34:00 GMT 2013

On Thu, Sep 26, 2013 at 8:34 AM, Ian Pilcher <> wrote:
> Short version:
> Can I use a thread-local sig_atomic_t in a signal handler?  I.e.:
>   static __thread volatile sig_atomic_t exit_flag = 0;
>   static void handler(int signum __attribute__((unused)))
>   {
>       exit_flag = 1;
>   }
> (Signals will be sent to specific threads with pthread_kill.)

Yes.  This is one of the few valid uses of volatile in a
multi-threaded program.

That said, a warning: if you put this code in a shared library and
open it with dlopen it may fail in a rather peculiar way.  See
I think this behaviour is a bug, but I'm not sure everyone agrees with
me, and in any case it has not been fixed.


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