Session Locking

bash

# Make sure you copy-paste all commands, so there is no delay between them

wget -q http://localhost/test.php -O first.txt &
sleep 1s
wget -q http://localhost/test.php -O second.txt
cat first.txt second.txt

output

3.1705009937286
5.171688079834

The second request will be always take 2 seconds more to finish, because its waiting for the first request to be completed.

test.php

<?php
session_id('sessionConcurrentTest');
session_start();

sleep(3);

echo (microtime(true) - $_SERVER['REQUEST_TIME']) . PHP_EOL;