Question

I’m using Thread::Pool::Simple for multi-threading.
I have a couple of questions which are quite general to multi-threading, I guess:

Each of my threads might die if something unexpected hapens. This is totally accepted by me, since it means some of my assertion are wrong and I need to redesign the code. Currently, when any thread dies the main program (calling thread) also dies, yielding something like:

Perl exited with active threads:
    0 running and unjoined
    0 finished and unjoined
    4 running and detached

1. Are these “running and detached”
   zombies? Are they “dangerous” in any
   way? Is there a way to kill all of
   them if any of the threads dies?
   What is the common solution for such
   scenarios?
2. Generally, my jobs are independent.
   However, I pass each of them as an
   argument a unique hash which is
   taken form one big hash oh hashes.
   the thread might change this
   personal hash (but it can’t get to
   the large hash – it doesn’t even
   know about it). Hence, I guess I
   don’t need any locks etc. Am I
   missing anything?

Answer 1

When your main program exits, all threads are terminated.

Perl threads work in one of two ways.

1) You can use join:

my $thr = threads->create(...);
# do something else while thread works
my $return = $thr->join(); # wait for thread to terminate and fetch return value

2) You can use detach:

my $thr = threads->create(...);
$thr->detatch(); # thread will discard return value and auto-cleanup when done

That message lists the threads that hadn’t been cleaned up before the program terminated.
“Running and unjoined” is case 1, still running. “Finished and unjoined” is case 1, finished but the return value hasn’t been fetched yet. “Running and detached” is case 2, still running.

So it’s saying you have 4 threads that had been detached but hadn’t finished before the program died. You can’t tell from that whether they would have finished if the program had run longer, or they were stuck in an infinite loop, or deadlocked, or what.

You shouldn’t need any locks for the situation you describe.