(PHP 4, PHP 5, PHP 7, PHP 8)
usleep — Delay execution in microseconds
Delays program execution for the given number of microseconds.
microsecondsHalt time in microseconds. A microsecond is one millionth of a second.
Note: Values larger than
1000000(i.e. sleeping for more than a second) may not be supported by the operating system. Use sleep() instead.
Note: The sleep may be lengthened slightly (i.e. may be longer than
microseconds) by any system activity or by the time spent processing the call or by the granularity of system timers.
No value is returned.
Example #1 usleep() example
<?php
// Current time
echo (new DateTime('now'))->format('H:i:s.v'), "\n";
// wait for 2 milliseconds
usleep(2000);
// back!
echo (new DateTime('now'))->format('H:i:s.v'), "\n";
// wait for 30 milliseconds
usleep(30000);
// back again!
echo (new DateTime('now'))->format('H:i:s.v'), "\n";
?>The above example will output:
11:13:28.005 11:13:28.007 11:13:28.037
the idea of sleep and usleep is that by letting the cpu run a few idle cycles so the other programs can have some cycles run of their own. what results in better response times and lower overall system-load. so if you have to wait for something, go to sleep for a few seconds instead of occupying the cpu while doing absolute nothing but waitting.On both MacOS X and Linux the usleep() call seems to consume CPU cycles, whereas sleep() and time_nanosleep() do not. This was the same on PHP 5.3.29 and 5.5.29.
I used a loop with just a call to sleep/usleep/time_nanosleep, and compared them all with an empty loop. Obviously the empty loop consumed 99% of the CPU, sleep used 0%, usleep used 3% for 1000ms and 6% for 100ms, and time_nanosleep used 0% for both 500ms and 1000ms.It should be noted that Windows machines have a resolution of either 10 mS or 15 mS (depending on the chipset implementation and HAL used) when using the Sleep() function in kernel32.dll. This means that your average error will be either 5 or 7.5 mS. This is not ordinarily a problem unless you really NEED to sleep for less time than the granularity provided by Windows.Should be noted that functions that loop really fast to create a delay also consume 100% CPU while doing the loop. Try creating a dummy loop that goes 100000 times, watch it choke your machine. If you really need usleep() don't use windows.If you're using Windows then you maybe are in trouble with usleep if you really need to use it.
The Bernie's microdelay function using fsockopen does not work properly, and the fclose doesn't help much.
I don't know if network connections go strange, but I know it does not work since you've made more than 2000 - 3000 calls to it, so it's not a reliable solution in 'long life' php scripts, or these are the issues of the microdelay function in my PHP and PHP-GTK applications.
Though another solution should be found, and googling a bit I fount a WinAPI function: Sleep.
So I get with this snippet wich works fine for me, you get milliseconds precission but the more important, it works for long-run scripts and of course, it does not waste any CPU cycles.
dl('php_w32api.dll');
$GLOBALS['win32api'] =& new win32;
// USleep alternative for Windows and PHP4:
$GLOBALS['win32api']->registerfunction("long Sleep (long dwMillisecods) From kernel32.dll");
// Now you can call the function from everywhere in your script: $GLOBALS['win32api']->Sleep(milliseconds);
for ($msec = 2000; $msec > 0; $msec = $msec - 125) {
echo "Hi. Next one in $msec msec.\n";
$GLOBALS['win32api']->Sleep($msec);
}A word of warning about the microdelay() code posted that uses the fsockopen - if you use this is a loop that delays for small periods you will very quickly run out of sockets/socket buffer space. And then your network connections go very strange......I have spent DAYS trying to create a reliable usleep()-replacement for Windows.
I have only this to offer:
As commented by someone else already, the gettimeofday() method used below is useless - PHP will use all available CPU power doing nothing.
The fsockopen() method apparently is also useless - as someone else commented, an fclose() was missing in the original post, but this apparently does not solve the problem. After calling the function about 50 or so times, fsockopen() returns immidiately, without any delay - and watching a process monitor in Windows, you can then watch the process taking up increasingly more memory, until eventually PHP aborts (or crashes) when it reaches maximum.
The win32api-method is also a no-go ... after calling the Sleep function a few hundred times (during which memory usage will also go up every time due to a memory leak somewhere), PHP will cause an exception and Windows will terminate it.
I have given up - I don't think there is any viable solution to this problem under PHP 4.
If you need this function, upgrade your project to PHP 5.
Or settle for 1-second delays with the sleep()-function.
These, unfortunately, seem to be your only options...Dude you are SO the man for that code snippet. It worked like a charm. I just wanted to point out a couple things and offer my own improvement.
1. If you're like me, you were probably wondering why the socket had to keep being recreated on each call, and why you couldn't just create a static socket. Its because socket_select assumes you're passing in a pointer, and will alter the variable on return to reflect the actual sockets that were changed.
2. I couldn't figure out for the life of me why socket_select wasn't defined. Its because you hadn't enabled the right extension in php.ini
Ok so heres my slight improvement. The only real thing I did is use a static variable for the socket, to avoid creating a brand new socket on each call of this function. I'm not sure if socket creation will cause things to crash down the line like the other problems reported on here, but if you ask me better safe then sorry.
function Sleeper($mSec)
{
// For dummies like me who spent 5 minutes
// wondering why socket_create wasn't defined
if(!function_exists('socket_create')){
die("Please enable extension php_sockets.dll");
}
// So the socket is only created once
static $socket=false;
if($socket===false){
$socket=array(socket_create(AF_INET,SOCK_RAW,0));
}
$pSock=$socket;
// Calc time
$uSex = $mSec * 1000;
// Do the waiting
socket_select($read=NULL,$write=NULL,$pSock,0,$uSex);
// OCD
return true;
}Note that this function has an overhead!
Example:
<?php
for ($i = 0; $i < 1000000; ++$i)
{
usleep(1);
}
?>
This block is running about 70 seconds on my server.
Script take about 70 microseconds for every usleep() function call.To monitor a scripts CPU ussage and avoid any nasty CPU gobbling loops you can use this function (will not work with windows or safe mode) I know it works on FreeBSD:
function phpmon($max)
{
$cmd = `ps -Unobody -r -o%cpu`;
$lines = explode("\n", $cmd);
$usage = substr($lines[1], 0, strpos($lines[1], "."));
$sleeprate = 500;
while ($usage >= $max)
{
$cmd = `ps -Unobody -r -o%cpu`;
$lines = explode("\n", $cmd);
$usage = substr($lines[1], 0, strpos($lines[1], "."));
usleep($sleeprate);
}
}
phpmon($MAX);
where $MAX is the maximum CPU you want the process to consume. e-mail me with any improvements/suggestions.
I have noticed that this consumes a lot of system CPU (at least in my limited testing) possibly from all of the system calls or the huge mathematical functions I used to test the effectiveness of the script.