<?php
$sleep = 0;
if (isset($_GET['sleep'])) {
    $sleep = $_GET['sleep'];
}

$pdo = new PDO('mysql:host=localhost;dbname=test', 'root', 'xxxxxx');
$pdo->beginTransaction();
$data = $pdo->query('SELECT counter FROM foo WHERE id=1 FOR UPDATE', PDO::FETCH_ASSOC);

foreach ($data as $row) {
    $c = $row['counter'];
}
++$c;

sleep($sleep);
$state = $pdo->query("UPDATE foo SET counter = $c WHERE id=1");
$res = NULL;
if ($state) {
    $res = $state->execute();
}
$pdo->commit();

echo $c;
var_dump($res);
var_dump($state);
exit;