What is a practical use for PHP's sleep()?

Question

I just had a look at the docs on sleep().

Where would you use this function?

Is it there to give the CPU a break in an expensive function?

Any common

Answer 1

Old question I know, but another reason for using u/sleep can be when you are writing security/cryptography code, such as an authentication script. A couple of examples:

1. You may wish to reduce the effectiveness of a potential brute force attack by making your login script purposefully slow, especially after a few failed attempts.
2. Also you might wish to add an artificial delay during encryption to mitigate against timing attacks. I know that the chances are slim that you're going to be writing such in-depth encryption code in a language like PHP, but still valid I reckon.

EDIT

Using u/sleep against timing attacks is not a good solution. You can still get the important data in a timing attack, you just need more samples to filter out the noise that u/sleep adds.

You can find more information about this topic in: Could a random sleep prevent timing attacks?