use warnings;
use strict;

use Parallel::ForkManager;
use DBI;

my $db_file = 'test.db';

my $dbh = DBI->connect(
    "dbi:SQLite:dbname=$db_file",
    "",
    "",
    {RaiseError => 1}
) or die $DBI::errstr;

my $pm = Parallel::ForkManager->new(20);

for (1..2){
    $pm->start and next;
    my $interval = $_ / 5;

    my $dbh = DBI->connect(
        "dbi:SQLite:dbname=$db_file",
        "",
        "",
        {RaiseError => 1}
    ) or die $DBI::errstr;

    while (1){
        dbwrite($dbh, $interval);
        #sleep 1;
    }
}

while(1){
    my $sth = $dbh->prepare(
        "SELECT * FROM test WHERE id=?;"
    );
    $sth->execute('test');
    my $val = $sth->fetchrow_hashref()->{value};
    print "$val\n";
}

sub dbwrite {
    my ($dbh, $interval) = @_;
    my $sth = $dbh->prepare(
        'UPDATE test SET value=? WHERE id="test";'
    );
    $sth->execute($interval);
};