To avoid that error, you must "return from the thread" first, then join it. If the thread was detached, no need to join, but you won't be able to get a return value. So remember, the thread must

1. Reach the end of it's code block(or return).

2. Must be joined, unless it was detached.

Here is a simple example, where I use a "goto FINISH" to force the thread to the end of it's code block, but I could have used "return". Now, if you want to kill a thread(s) prematurely, just set it's 'die' signal to one and join it.

#!/usr/bin/perl
use warnings;
use strict;
use threads;
use threads::shared;
$| = 1;

my %threads;

foreach (1..10){
  share ($threads{$_}{'die'});
  $threads{$_}{'die'} = 0; 
}

foreach (1..10) {
    $threads{$_}{'thread'} = threads->new('StartTest');
}

my @threads = (1..10);
foreach(@threads){
    $threads{$_}{'die'} = 1;
    $threads{$_}{'thread'}->join;
}

print "\n", "All threads done\nHit Enter to exit\n";
<>;
##########################################################

sub StartTest {
    my $self = threads->self;

    print "Thread ", $self->tid, " started\n";
    
    while(1){
    if( $threads{$_}{'die'} == 1){goto FINISH}
       else{ select(undef,undef,undef, 5) };
    }
FINISH:    
    print "Thread ", $self->tid, " ending\n";
}
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