DROP TABLE IF EXISTS test;

CREATE TABLE test (
    id VARCHAR(50),
    value VARCHAR(20)
);

INSERT INTO test VALUES ('test', 0);

##</code><code>##

use warnings;
use strict;

use DBI;
use Parallel::ForkManager;

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

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

for (1..20){
    $pm->start and next;
    my $interval = $_ / 10;
    while (1){
        dbwrite($dbh, $interval);
        #print "$interval\n";
    }
}

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

    #sleep 1;
}

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