Perl: Error handling threads - multithreading

Question

sub worker {
exit 1;
}
my $thr = threads->create(\&worker);
while ($thr->is_running()) {
print "running\n";
}
my $rc = $thr->join();
exit $rc;
I come from Python. Is there something similar to try/except that I can use around while($thr->is_running)
I get (because I exit 1 in worker):
Perl exited with active threads:
0 running and unjoined
1 finished and unjoined
0 running and detached
I want to be able to catch the exit or other compiliation error worker might have
use strict;
use warnings;
use threads;
sub worker {
my $bad = 1/0;
}
my $thr = threads->create( \&worker );
while ( $thr->is_running() ) {
sleep 1;
}
my $rc = $thr->join(); #NB - RC will be 'undef' because there's no return.
OUTPUT:
Thread 1 terminated abnormally: Illegal division by zero at mythread.pl line 6.
Is it possible to catch it the error? and how and where?

Answer 1

Don't call exit in your thread. That exits your whole program. threads -> exit is what you want.
http://perldoc.perl.org/threads.html#EXITING-A-THREAD
threads->exit()
If needed, a thread can be exited at any time by calling threads->exit() . This will cause the thread to return undef in a scalar context, or the empty list in a list context.
When called from the main thread, this behaves the same as exit(0).
join waits for the thread to complete.
Don't use $a. It's a bad variable name anyway, but it's also used for perl sort.
You're capturing $rc but that implies a return in your thread. As it, it'll be undefined.
But this will work:
use strict;
use warnings;
use threads;
sub worker {
sleep 10;
threads->exit;
}
my $thr = threads->create( \&worker );
while ( $thr->is_running() ) {
print $thr ->tid, " running\n";
sleep 1;
}
print $thr ->tid, " not running\n";
sleep 5;
my $rc = $thr->join(); #NB - RC will be 'undef' because there's no return.
In the latter case, $rc is undef because you exited. You can test for it being undefined if you want to trap an abnormal exit. (Just make sure you do actually return something on a success).
Alternatively, wrap your code in the thread with an eval because that won't be a fatal error. Doesn't come up too often, but I'd suggest rather than trying to capture the broad spectrum of possible fatal errors, you're far better off just testing whether it completed successfully instead.
To answer your second question - something like this:
use strict;
use warnings;
use threads;
sub worker {
sleep 5;
my $fatal = 1 / 0;
return 1;
}
sub otherworker {
sleep 4;
eval { my $fatal = 1 / 0; };
if ($#) { return $# }
else { return "No error" }
}
my $thr = threads->create( \&worker );
my $thr2 = threads->create( \&otherworker );
while ( $thr->is_running() ) {
print $thr ->tid, " running\n";
sleep 1;
}
print $thr ->tid, " not running\n";
foreach my $thread ( threads->list ) {
my $return_code = $thread->join;
if ( not defined $return_code ) {
print $thread ->tid(), ": terminated abnormally\n";
}
else {
print $thread ->tid, ": exited with $return_code \n";
}
}