Re: SIGINT, longjmp, getaddrinfo

[Godmar Back <godmar at gmail dot com>]

On Tue, Feb 9, 2016 at 5:16 AM, Carlos O'Donell <carlos@systemhalted.org> wrote:
>
> On Tue, Feb 9, 2016 at 4:29 AM, Hal Murray <hmurray@megapathdsl.net> wrote:
>
> > The symptom is that ^C stopped working.  A few printf-s later, I discovered
> > that the SIGINT handler was being called with SIGINT masked.  Switching from

(Responding to original email:)

That's not really a surprise. SIGINT is always masked when the SIGINT
handler is called, read the documentation:
http://www.gnu.org/software/libc/manual/html_node/Blocking-for-Handler.html

"When a handler function is invoked on a signal, that signal is
automatically blocked"

>
> To reiterate: After jumping out of an AS handler you may only call
> AS-safe functions.

That's not always true in my opinion. It's true only if the main code
was able to enter any C library function that is not AS-safe.

>
> It is not a can of worms.

It really kind of is, any signal handling has the potential to lead to
complex control flow.
Hopefully after this thread the original emailer will be able to
google it and find it confirmed here ;-)

>
> I expect that you really can't live with the above restriction of
> calling only AS-safe functions after the jump out of the signal
> handlers. Therefore you need to rework your code such that the AS
> handler sets a global that is inspected by the main loop.
> Alternatively use threads and pthread_cancel.

Another alternative is to rework the main code to block/mask the
SIGINT signal during any portion in which AS-unsafe functions may be
invoked. If his application involves large blocks of libc-unrelated
computation, that may be feasible without undue latency (he'd still be
able to longjmp out of the handler).

Personally, though, I agree that the global flag approach will likely be better.

 - Godmar