I tried the following on an IIS 6/PHP 5 machine:
function profiler($return = false)
static $m = 0;
if($return) return $m . " bytes";
if(($mem = memory_get_usage()) > $m) $m = $mem;
declare(ticks = 1);
$numbers = array();
for($i=0; $i<1000000; $i++)
print($i . "<br />");
...and got the following errors:
1) PHP has encountered an Unhandled Exception Code -1073741674 at 0435EC5A
2) PHP has encountered an Access Violation at 02727891
3) PHP has encountered an Access Violation at 02727879
4) PHP has encountered an Access Violation at 00000000
So far the code hasn't crashed the web server, but like the warning says, "register_tick_function() should not be used with threaded web server modules. Ticks are not working in ZTS mode and may crash your web server."
Strangely enough, the code does execute successfully every once in a while.