sleep(0) is valid

[BenMorel]

https://3v4l.org/qknjR

[weirdan]

What's the use-case though? Is it to yield CPU to other processes?

[BenMorel]

Our use case is a CLI that accepts an optional startup delay, and we do accept 0 seconds.

Anyway, I think Psalm should align with PHP's behaviour, that complains only for < 0?

[orklah]

We do have this issue too in our codebase. Our default sleep duration is 0 but can be changed. It feels cheap to make a special condition to avoid calling a sleep instruction that will do nothing

[weirdan]

There's a difference between not calling sleep() at all and calling it with 0 argument, most noticeable when the system is under load. E.g. running paratest on Psalm test suite with Xdebug enabled (to generate load) and the following script in parallel:

<?php

$s = microtime(true);
$t = $argv[1];
if ($t >= 0) {
    sleep($argv[1]);
}

var_dump('elapsed', number_format(microtime(true) - $s, 6));

I get:

$ time php qq.php -1                                                                                     
string(7) "elapsed"
string(8) "0.000018"
user=0.14s system=0.05s cpu=19% total=0.980

$ time php qq.php 0
string(7) "elapsed"
string(8) "0.014775"
user=0.16s system=0.03s cpu=20% total=0.929

(LA ~10).

So 0 is not totally useless, as it does produce measurable effect.

[weirdan]

Thanks!

[orklah]

Is it any different than another "no-action" function call? Let's say strtolower on an empty string?

[weirdan]

It is.

Quoting nanosleep() man page (sleep() is using nanosleep() under the hood):

nanosleep() suspends the execution of the calling thread until either at least the time specified in *req has elapsed, or [...]
Furthermore, after the sleep completes, there may still be a delay before the CPU becomes free to once again execute the calling thread.

The net effect of that is that the longer the CPU runqueue, the later your process will be waked up, on average. sleep(0) still suspends your process, and it then must wait its turn to use the CPU again.

[orklah]

Good to know, thanks!