[PHP-DEV] Interesting sleep() side-effect From: Rasmus Lerdorf (rasmus <email protected>)
Date: 01/27/99

In testing Thies' connection abort detection code, completely unrelated to
his stuff, I noticed an interesting side-effect of calling sleep() in a
PHP script. I have tried this on both Linux and Solaris and get the same
results. Could you guys with access to other OS'es try this one?

<?
    set_time_limit(5);
    register_shutdown_function("done");
    function done() {
        global $i;

        $fp = fopen("/tmp/done","w");
        fputs($fp,"i reached $i\n");
        fclose($fp);
    }

    for($i=0; $i<30000; $i++) {
        for($j=0;$j<1000;$j++) $a=sqrt($j);
        /* sleep(1); */
        echo "$i ................................................................................<br>";
        flush();
    }
?>

This script should run for 5 seconds, unless of course you are on a
massively fast machine that can do 30000 sqrt()'s in 5 seconds. However,
when you uncomment the sleep(1) call there, it will happily run way past 5
seconds. Looks to me like the sleep() system call is interfering with our
itimer. The man pages state that sleep() may be implemented as a SIGALRM,
but we are using a SIGPROF itimer, so I thought we were actually safe
here.

It doesn't worry me too much. It is more an interesting side effect, but
something we might want to document as a caveat in the sleep()
documentation. I would be intersted in hearing if this behaviour is
consistent across all the operating systems.

The "/tmp/done" file is not related to this particular message. That's
just how I am testing to see if PHP catches when the client closes the
socket.

-Rasmus 

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