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Postings from January 2005
On Wed, 2005-01-26 at 15:24, Ton Hospel wrote:
> In article <rt-3.0.11-33940-106489.16.0611746958661@perl.org>,
> "Victor Porton,,," (via RT) <perlbug-followup@perl.org> writes:
> > I reasonably detailed scanned perlobj, perltoot, perlbot manpages,
> > read "die" and "eval" entries in perlfunc and found no answer.
> >
> > The questions answer to which seems missing in Perl docs is:
> >
> > Consider code:
> >
> > eval {
> > my $obj1 = Class1->new;
> > {
> > my $obj2 = Class2->new;
> > # Suppose Class2->DESTROY calls 'die "2"'
> > }
> > # Suppose Class1->DESTROY also 'die "1"'
> > }
> >
There are TONS of edge cases (and not so edge cases) around eval/die
semantics. They'll all confuse you at first. The one that bit me hardest
was actually fairly simple:
$start = time();
@lines = eval {
$SIG{ALRM} = sub {die "timeout"};
alarm(2);
my $cmd = IO::File->new("sleep 5|");
$cmd->getlines();
};
die $@ if $@ && ($@ !~ /timeout/);
$end = time();
$delta = $end-$start;
print "Got ",scalar(@lines)," answers in $delta seconds.\n";
Of course, this fails (exits in the full 5 seconds) unless you move the
declaration of $cmd outside of the eval so that destruction doesn't
attempt to wait(2) on the child, but that's very non-obvious to someone
who is thinking in terms of "my signal handler said die, so we jump
outside of the eval."
I really wish at times that Perl had a safe eval that you could
absolutely exit from.
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