use strict;
use warnings;

use threads;
use Thread::Queue;

use IO::File;

my $q = Thread::Queue->new();

sub worker {
    
    my $counter = 1;
    my $number_of_lines = 0;
    
    open my $fh, ">", "log" . $counter++ . ".txt" or die $!;
    $fh->autoflush(1);
     
    while (1) {
        
        my $thread_id = $q->dequeue();
            
        if ( $number_of_lines >= 20 ) {
            
            close $fh;
            open $fh, ">", "log" . $counter++ . ".txt" or die $!;
            $fh->autoflush(1);
            
            $number_of_lines = 0;
        }
        
        print $fh "This is a very long string containing $thread_id\n";
        $number_of_lines++;
    }
}

threads->new( \&worker )->detach();

my @threads;
foreach my $thread_id ( 0 .. 10 - 1 ) {
    
    my $thread = threads->create( 'start_thread', $thread_id );
    push @threads, $thread;
}
    
foreach my $thread (@threads) {

    $thread->join();
}

sub start_thread {
    
    my ( $thread_id ) = @_;
    
    while (1) {
        
        $q->enqueue($thread_id);
        sleep 1;
    }
}