How to prevent multiple requests from being submitted simultaneously to the same address at the same time in PHP

How to prevent multiple requests from being submitted simultaneously to the same address at the same time in PHP
Title, for example, there is a method in which the logic is probably as follows:


function Test () {
$a = $db->query (' ... ');//returns 1 or 0
if ($a = = 1) {
$db->set (0);//The next execution of this method after the update is no longer 1.
Here is the other logic, the problem is that if many requests call this method at the same time, and the set procedure in this method is a little longer, then the logic here will be executed multiple times, which is inconsistent with the expected execution only once.
}
}


How do you generally deal with this situation? This is a lot of the case with high security requirements such as voting or prizes.
If the request may come from a different IP, if you use a cache such as memcached to save the state, there is also a network delay, SHMOP.

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