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proc_nice

(PHP 5, PHP 7, PHP 8)

proc_niceChange the priority of the current process

Description

proc_nice(int $priority): bool

proc_nice() changes the priority of the current process by the amount specified in priority. A positive priority will lower the priority of the current process, whereas a negative priority will raise the priority.

proc_nice() is not related to proc_open() and its associated functions in any way.

Parameters

priority

The new priority value, the value of this may differ on platforms.

On Unix, a low value, such as -20 means high priority whereas positive values have a lower priority.

For Windows the priority parameter has the following meaning:

Priority class Possible values
High priority priority < -9
Above normal priority priority < -4
Normal priority priority < 5 & priority > -5
Below normal priority priority > 5
Idle priority priority > 9

Return Values

Returns true on success or false on failure. If an error occurs, like the user lacks permission to change the priority, an error of level E_WARNING is also generated.

Changelog

Version Description
7.2.0 This function is now available on Windows.

Examples

Example #1 Using proc_nice() to set the process priority to high

<?php
// Highest priority
proc_nice(-20);
?>

Notes

Note: Availability

proc_nice() will only exist if your system has 'nice' capabilities. 'nice' conforms to: SVr4, SVID EXT, AT&T, X/OPEN, BSD 4.3.

Note: Windows only

proc_nice() will change the current process priority, even if PHP was compiled using thread safety.

See Also

add a note

User Contributed Notes 5 notes

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7
kevin AT REMOVETHIS mrkmg.com
10 years ago
On a Linux system, running apache2 as a non-privileged user you can not increase the niceness of the process after decreasing it. Also, you can not use the apache_child_ terminate either. I found the following does work though:

<?php

//decrease niceness
proc_nice(19);

//kill child process to "reset" niceness
posix_kill( getmypid(), 28 );

?>
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3
php at richardneill dot org
13 years ago
If a process is reniced, then all its children inherit that niceness. So a PHP script can call proc_nice on itself, then invoke system(), and the command executed via system() will also be niced.

Also worth making a note of ionice. There's no PHP function for this, but it's important. A nice'd program will happily try to chew up all i/o bandwidth with very little CPU usage, it can therefore make the entire computer non-responsive despite the programmer's intention. Use "ionice -c3" or see "man ionice"
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2
Marek
13 years ago
Regarding ionice - on linux the impact of the ionice -c3 class is similar to that of nice, because the CPU "niceness" is taken into account when calculating the io niceness.
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0
phil_php at zieaon dot com
2 years ago
It is important to note that this is a relative change. I didn't read the description properly and couldn't figure out why setting proc_nice(0) didn't take the forked children back to 0!
For example if you run:
<?php
proc_nice
(-5);
proc_nice(0); // will have no effect
proc_nice(5); // will take the niceness back to 0

?>

In PHP CLI under Debian (and probably many other Linux flavours) you can read the 'niceness' from the proc filesystem. (There may be a PHP command that gives this info but there doesn't seem to be a link to it on this page.)
E.g
<?php
$Current_Niceness_Value
= intval(explode(" ",file_get_contents("/proc/".getmypid()."/stat"))[18]);

// Note: Older versions of Linux return an unsigned integer which has to be converted to a signed integer.
$Current_Niceness_Value = unpack("l",pack("L",intval(explode(" ",file_get_contents("/proc/".getmypid()."/stat"))[18])))[1];

?>
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0
pandi at home dot pl
15 years ago
Simple function for check process nice, by default returns nice of current process:

<?php

public static function getProcessNice ($pid = null) {
if (!
$pid) {
$pid = getmypid ();
}

$res = `ps -p $pid -o "%p %n"`;

preg_match ('/^\s*\w+\s+\w+\s*(\d+)\s+(\d+)/m', $res, $matches);

return array (
'pid' => (isset ($matches[1]) ? $matches[1] : null), 'nice' => (isset ($matches[2]) ? $matches[2] : null));
}

?>
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