商城秒杀不超卖思路，附php伪代码

<?php
header("content-type:text/html;charset=utf-8");
$t_start_set = microtime(true);
$redis = new redis();
$result = $redis->connect('127.0.0.1', 6379);
$goods_id=22;
$redis->watch("watchGoods_".$goods_id);
$len = $redis->hlen("watchGoods_".$goods_id);//已抢购数量
$rob_total = $redis->get('Goods_'.$goods_id.'_totalNum'); // $redis->set('Goods_'.$goods_id.'_totalNum',100) 抢购数量(库存总数)设置100件
if ($len < $rob_total) {
    $redis->multi();
    $redis->hSet("watchGoods_".$goods_id, "user_id_" . mt_rand(1, 999999) .'=====:'.$len, $t_start_set.'->'.microtime(true));//hash表
    $rob_result = $redis->exec();
     if ($rob_result) {
           file_put_contents("log.txt", '时间: '.$t_start_set." 进入  success ! 抢到了第:".($len+1).'个商品，库存数量='.($rob_total- $len-1).PHP_EOL, FILE_APPEND);
            $mywatchlist = $redis->hGetAll("watchGoods_".$goods_id);
            echo "抢购成功！<br/>";
            echo "剩余数量：" . ($rob_total - $len - 1) . "<br/>";
            echo "用户列表：<pre>";
            var_dump($mywatchlist);
        } else {
            file_put_contents("log.txt", '时间: '.$t_start_set.' 进入 ERROR！！手气不好，再抢购 CAS啦 准备抢第'.($len+1).'个，但是CAS机制，别人抢走了。' . PHP_EOL, FILE_APPEND);
            exit;
        }
} else {
  file_put_contents("log.txt", '时间: '.$t_start_set.'进入. ^_^ 抢购结束 抢光了 over='.$len . PHP_EOL, FILE_APPEND);
  $mywatchlist1 = $redis->hGetAll("watchGoods_".$goods_id);
   echo "用户列表：<pre>";
  var_dump($mywatchlist1);
}?>

秒杀思路：

1.使用redis 结合watch的乐观锁的特性。CAS[check-and-set OR compare and swap]

  参考 http://www.csdn.net/article/2014-11-28/2822858 

        http://www.cnblogs.com/martinzhang/p/3415204.html

2. CAS

   参考 http://blog.csdn.net/chen19870707/article/details/41083183
          http://www.cnblogs.com/Mainz/p/3546347.html   
          http://flychao88.iteye.com/blog/2269438

          http://coolshell.cn/articles/8239.html