Front page | perl.perl5.porters |
Postings from January 2005
>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."
If the child wait is the culprit, I'm confused why this behaves differently:
# my $cmd = IO::File->new("sleep 5|");
my $cmd = IO::File->new("cat /dev/zero|");
The 2 second timeout works as expected now; whereas, the potentially dueling duo
(alarm/sleep) in your example seem risky...
--
Charles DeRykus