Redis version flash kill exercise

<?php

$redis = new Redis();
$redis->connect('127.0.0.1', 6379);

$UserID = (int) $_GET['UserID'];
$ActivityID = (int) $_GET['ActivityID'];

// 库存检查
if ($redis->decr('Amount') < 0) {
	$redis->incr('Amount');
	echo '{ "exception" : "InvalidNumberException" }';
	exit;
}

// 直接入库
$NoRepeat = $redis->hSet('UserList', $UserID, sprintf('{ "ActivityID" : %d, "Milliseconds" : "%.0f" }', $ActivityID, round(microtime(true) * 1000)) );
if (!$NoRepeat) {
	
	// 还原库存
	$redis->incr('Amount');
	echo '{ "exception" : "SaveInvalidException" }';
	exit;
}

echo sprintf('{ "errno" : 0 , "data" : { "UserID" : %d, "Milliseconds": %.0f } }', $UserID, round(microtime(true) * 1000));
exit;