[totony]

Most operating systems will not idle on a sleep() call, as far as I remember. Since the server is executing multiple applications, it is very likely that the processor will be assigned to another running application. The only way to really know this would be to know the state of the specific process php is using for the request, which seems unfeasible in a production environment (except if you have admin of course).

[ircmaxell]

Well, it won't idle if there is another process ready to execute (load is greater than 1). If there is no process wanting to execute, it will idle.

Again, I'm not saying this is practical. I'm saying it might be possible (even if improbable).

And don't get me wrong, I'm not saying "OMG YOU ARE BAD IF YOU DON"T PROTECT THIS RIGHT". I'm more leaning on the side of "if there's a chance, I assume someone could possibly figure out a way".