Sample parallel test for php

parallel-test.php

<?php

try {
	
	$db = new PDO('mysql:host=127.0.0.1;dbname=parallel_test', '', '');
	$db->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);

	$requested_stock = (int) $_REQUEST['requested_stock'];
	$item_id = (int) $_REQUEST['id'];

	$product = $db->prepare("select stock from items where id = ? limit 1 for update");
	$product->execute([
		$item_id
	]);


	$product = $product->fetchAll(PDO::FETCH_OBJ);

	if ($product[0]->stock > $requested_stock) {
		
		$update_stock = $db->prepare("update items set stock = ? where id = ? limit 1");
		$update_stock->execute([
			($product[0]->stock-$requested_stock),
			$item_id
		]);

		echo "Product updated.";
	}
	else {

		echo "Unsufficient stock.";
		
	}
} catch (PDOException $e) {
	
	die($e->getMessage());
}