Date: Wed, 12 Jan 2000 20:33:32 -0500 From: Laurence Berland <stuyman@confusion.net> To: freebsd-questions@FreeBSD.ORG Subject: Re: Giving a sighandler more information Message-ID: <387D2B6C.4E2E42C1@confusion.net> References: <200001122054.VAA52051@dorifer.heim3.tu-clausthal.de>
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Followup question: is a sig_atomic_t appropriate to hold the value of a
FILE * ?
Oliver Fromme wrote:
>
> Laurence Berland <stuyman@confusion.net> wrote in list.freebsd-questions:
> > Oliver Fromme wrote:
> >> Seriously. You _must_ declare global variables which are
> >> accessed from a signal handler as ``volatile sig_atomic_t''.
> >> Everything else is _not_ guaranteed to work (and if it works,
> >> then it's just pure luck).
> >
> > Does this have something to do with the signal being caught while we're
> > in the signal routine? Am I on the right track?
>
> No. The problem is that a signal handler can be called at
> any time, basically, even in the midst of a memory access
> (depending on the platform). The standard guarantees that
> accesses to variables of type "sig_atomic_t" are always
> atomic (hence the name), i.e. they cannot be interrupted
> by a signal handler.
>
> The "volatile" qualifier makes sure that the compiler does
> not try certain optimizations on these variables, such as
> caching them in registers (which could also break signal
> handlers, because the contents of the actual variable might
> be incorrect if it's cached).
>
> Regards
> Oliver
>
--
Laurence Berland, Stuyvesant HS Debate
<><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
Windows 98: n.
useless extension to a minor patch release for
32-bit extensions and a graphical shell for a
16-bit patch to an 8-bit operating system
originally coded for a 4-bit microprocessor,
written by a 2-bit company that can't stand for
1 bit of competition.
http://stuy.debate.net
icq #7434346 aol imer E1101
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