What is thread safe and non-thread safe in PHP? How to choose the correct version?

Hello everyone! I'm a beginner in PHP, and when downloading the PHP distribution from the official website, I see two versions: "Thread Safe" (TS) and "Non-Thread Safe" (NTS). Honestly, I don't understand the difference and don't know which one to choose. I'm using XAMPP on Windows and writing simple websites. But recently I tried to write a script that sends email notifications in a loop. Here's the simplified code: ```php ``` When I run this script, the page loads very slowly, and I thought it could be sped up using threads. I found the pthreads extension, but it requires the Thread Safe version of PHP. However, I read that if