On Jun 18, 6:50 am, rvtol+use...@isolution.nl ("Dr.Ruud") wrote:
> On 2011-06-17 05:34, C.DeRykus wrote:
>
>
> > Ruud:
> >> C.DeRykus:
> >>> Ruud:
> >>>> C.DeRykus:
> >>>>> Another solution, not necessarily more elegant, but
> >>>>> more familiar to most is an eval {} and alarm pair:
>
> >>>>> EVAL: {
> >>>>> eval {
> >>>>> local $SIG{ ALRM } = sub { die "alarm"; };
> >>>>> local $SIG{ USR1 } = sub { die "usr1" };
> >>>>> alarm $sleeptime;
> >>>>> ... some long running operation here ....
> >>>>> alarm 0;
> >>>>> 1;
> >>>>> } or do {
>
> >>>> Insert:
> >>>> my $eval_error = $@ || "Zombie error!";
>
> >>> Huh? If you insert that statement before doing 'alarm 0',
> >>> then, there's a potential have a race condition with the
> >>> alarm going off and terminating the entire program with
> >>> "alarm clock" before you can even check $@.
>
> >> Realize that the alarm is then already reset (to the earlier setting)
> >> because the localization gets out of scope.
>
> > No, that's not true. The localized signal handler gets
> > reset but any alarm that is started in that scope will
> > still be delivered to the current signal handler unless
> > turned off.
>
> Right, but the word "alarm" in my sentence stood for "alarm signal
> handler", so please re-read.
>
>
I'm sorry to have mis-read your response. With
just a signal name, I always tend to interpret it
narrowly as the signal itself and not the handler.
> >>> eval { ... ; "foo" happens and sets $@='bar';
> >>> ...
> >>> };
> >>> my $eval_error = $@ || "Zombie error!";
> >>> # alarm actually does go off now
> >>> # and terminates program
> >>> alarm 0; # too late
> >>> ....
> >>> Therefore you wouldn't want to insert any statement
> >>> before turning off the alarm.
>
> >> Because the alarm signal is localized (to the eval{}), it is not active
> >> in the do{}.
>
> > No, it's still active. In the case below, the alarm
> > that was set inside the scope gets delivered to
> > the default alarm handler.
>
> And my "alarm signal" was short again for "alarm signal handler".
>
> > On freebsd 8.2 for
> > instance:
>
> > $ perl -e 'eval{ local $SIG{ALRM}=sub{die "foo"};
> > alarm 1};<>'
> > Alarm clock: 14
>
> > So the alarm that was launched in the eval {} scope
> > is still active and, even though the localized handler
> > goes out of scope, the delivery still occurs later to
> > the default handler.
>
> Well, I hope I cleared up my bad phrasing.
Should have been clear to me in that context
what you were referring to. Turning off the
undelivered alarm is good practice but I'll
re-read the whole thread.
--
Charles DeRykus
.
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