The lock-file mechanism in Kevin Trass's note is incorrect because it is subject to race conditions.
For locks you need an atomic way of verifying if a lock file exists and creating it if it doesn't exist. Between file_exists and file_put_contents, another process could be faster than us to write the lock.
The only filesystem operation that matches the above requirements that I know of is symlink().
Thus, if you need a lock-file mechanism, here's the code. This won't work on a system without /proc (so there go Windows, BSD, OS X, and possibly others), but it can be adapted to work around that deficiency (say, by linking to your pid file like in my script, then operating through the symlink like in Kevin's solution).
#!/usr/bin/php
<?php
define('LOCK_FILE', "/var/run/" . basename($argv[0], ".php") . ".lock");
if (!tryLock())
die("Already running.\n");
# remove the lock on exit (Control+C doesn't count as 'exit'?)
register_shutdown_function('unlink', LOCK_FILE);
# The rest of your script goes here....
echo "Hello world!\n";
sleep(30);
exit(0);
function tryLock()
{
# If lock file exists, check if stale. If exists and is not stale, return TRUE
# Else, create lock file and return FALSE.
if (@symlink("/proc/" . getmypid(), LOCK_FILE) !== FALSE) # the @ in front of 'symlink' is to suppress the NOTICE you get if the LOCK_FILE exists
return true;
# link already exists
# check if it's stale
if (is_link(LOCK_FILE) && !is_dir(LOCK_FILE))
{
unlink(LOCK_FILE);
# try to lock again
return tryLock();
}
return false;
}
?>
getmypid
(PHP 4, PHP 5, PHP 7, PHP 8)
getmypid — Restituisce l'ID del processo PHP
Descrizione
getmypid(): int
Restituisce l'ID del processo PHP, oppure false in caso errore.
Avviso
Gli ID di processo non sono univoci, poiché sono sorgenti di bassa entropia. Si raccomanda di non basarsi sul pid nei contesti basati sulla sicurezza.
Vedere anche getmygid(), getmyuid(), get_current_user(), getmyinode() e getlastmod().
add a note
User Contributed Notes 14 notes
Radu Cristescu ¶
11 years ago
Robert Mays Jr ¶
13 years ago
All of the examples above require you to have shell command execution turned on- this example uses only PHP functions and should work on any system (posix is included by default)-
the key is posix_getsid which will return FALSE if the processes does not exist.
<?php
$lockfile = sys_get_temp_dir() . '/myScript.lock';
$pid = file_get_contents($lockfile);
if (posix_getsid($pid) === false) {
print "process has died! restarting...\n";
file_put_contents($lockfile, getmypid()); // create lockfile
} else {
print "PID is still alive! can not run twice!\n";
exit;
}
?>
:-) perfect if you need to make sure a cron job or shell script has ended before it can be started again.
This works across users- if the cron job is started as 'root' your 'web user' can see if the process is still alive (useful for system status pages)
Kevin Traas (ktraas- at -gmail dot com) ¶
15 years ago
Looking to create a lock-file mechanism for a cmd-line script?
Enjoy!
#!/usr/bin/php
<?php
define( 'LOCK_FILE', "/var/run/".basename( $argv[0], ".php" ).".lock" );
if( isLocked() ) die( "Already running.\n" );
# The rest of your script goes here....
echo "Hello world!\n";
sleep(30);
unlink( LOCK_FILE );
exit(0);
function isLocked()
{
# If lock file exists, check if stale. If exists and is not stale, return TRUE
# Else, create lock file and return FALSE.
if( file_exists( LOCK_FILE ) )
{
# check if it's stale
$lockingPID = trim( file_get_contents( LOCK_FILE ) );
# Get all active PIDs.
$pids = explode( "\n", trim( `ps -e | awk '{print $1}'` ) );
# If PID is still active, return true
if( in_array( $lockingPID, $pids ) ) return true;
# Lock-file is stale, so kill it. Then move on to re-creating it.
echo "Removing stale lock file.\n";
unlink( LOCK_FILE );
}
file_put_contents( LOCK_FILE, getmypid() . "\n" );
return false;
}
?>
brospam at gmail dot com ¶
11 years ago
My lockfile system
<?php
function isLocked(){
if(file_exists(LOCK_FILE)) {
$lockingPID = trim(file_get_contents(LOCK_FILE));
$test=trim(`ps -p $lockingPID -o pid=`);
if(!empty($test)) return true;
echo "Removing stale lock file.\n";
unlink(LOCK_FILE);
}
file_put_contents(LOCK_FILE, getmypid()."\n");
return false;
}
?>
brooke at jump dot net ¶
21 years ago
One good use for this is deciding on a concurrency-safe temporary file or directory name. You can be assured that no two processes on the same server have the same PID, so this is enough to avoid collisions. For example:
<?php
$tmpfile = "/tmp/foo_".getmypid();
// Use $tmpfile...
// Use $tmpfile...
// Use $tmpfile...
unlink ($tmpfile);
?>
If you are sharing /tmp over the network (which is odd....) then you can, of course, mix in the PHP server's IP address.
wouter99999 at gmail dot com ¶
13 years ago
On windows, ps is not available. Instead, to view a list of running processes, you can use exec('tasklist'); To kill processes you can use exec('taskkill); Enter taskkill /? for more information.
Erickson Reyes ercbluemonday at yahoo dot com ¶
15 years ago
We also had this challenge in our company to prevent a php script in a cron job from overlapping each other.
We made this solution
<?php
// Initialize variables
$found = 0;
$file = basename(__FILE__);
$commands = array();
// Get running processes.
exec("ps w", $commands);
// If processes are found
if (count($commands) > 0) {
foreach ($commands as $command) {
if (strpos($command, $file) === false) {
// Do nothin'
}
else {
// Let's count how many times the file is found.
$found++;
}
}
}
// If the instance of the file is found more than once.
if ($found > 1) {
echo "Another process is running.\n";
die();
}
/**
*
* Regular process here...
*
*/
?>
kroczu at interia dot pl ¶
19 years ago
<?php
/*
mixed getpidinfo(mixed pid [, string system_ps_command_options])
this function gets PID-info from system ps command and return it in useful assoc-array,
or return false and trigger warning if PID doesn't exists
$pidifo=getpidinfo(12345);
print_r($pidifo);
Array
(
[USER] => user
[PID] => 12345
[%CPU] => 0.0
[%MEM] => 0.0
[VSZ] => 1720
[RSS] => 8
[TT] => ??
[STAT] => Is
[STARTED] => 6:00PM
[TIME] => 0:00.01
[COMMAND] => php someproces.php > logfile
)
*/
//////////////////////////////////////////////
function getpidinfo($pid, $ps_opt="aux"){
$ps=shell_exec("ps ".$ps_opt."p ".$pid);
$ps=explode("\n", $ps);
if(count($ps)<2){
trigger_error("PID ".$pid." doesn't exists", E_USER_WARNING);
return false;
}
foreach($ps as $key=>$val){
$ps[$key]=explode(" ", ereg_replace(" +", " ", trim($ps[$key])));
}
foreach($ps[0] as $key=>$val){
$pidinfo[$val] = $ps[1][$key];
unset($ps[1][$key]);
}
if(is_array($ps[1])){
$pidinfo[$val].=" ".implode(" ", $ps[1]);
}
return $pidinfo;
}
?>
eight_hf at live dot fr ¶
12 years ago
On Linux you can check if a process is still running by verifying if the PID exists in the /proc directory :
<?php
if(file_exists('/proc/'.$pid))
{
echo 'The process is still running.';
}
?>
pdc at example dot com ¶
12 years ago
Here is how you'd use exec on a posix system to accomplish counting processes quickly.
I want to know how many processes are running with 'update.php' in the command:
ps aux|grep "[u]pdate.php"|wc -l
(the trick of using [u]pdate.php instead of update.php makes sure that the grep command itself is not matched). Be sure to use quotes in the command, or it won't work either.
So, the code:
<?php
function countProcesses($scriptName)
{
// ps aux|grep "[u]pdate.php"|wc -l
$first = substr($scriptName, 0, 1);
$rest = substr($scriptName, 1);
$name = '"['.$first.']'.$rest.'"';
$cmd = "ps aux | grep $name | wc -l";
$result = exec($cmd);
return $result;
}
?>
Pure-PHP ¶
19 years ago
You can use this function also to avoid more than one instance of your app.
You can also use this class.
http://www.pure-php.de/node/20
Usage:
<?php
inlude("ProcessHandler.class.php");
if(ProcessHandler::isActive()){
die("Already running!\n";);
}else{
ProcessHandler::activate();
//run my app
}
?>
martijn at nowhere dot com ¶
8 years ago
On windows, you can get a list of PID's using this single line statement: <?php $pids = array_column(array_map('str_getcsv', explode("\n",trim(`tasklist /FO csv /NH`))), 1); ?>.
james at voodoo dot co dot uk ¶
14 years ago
The 'ps' command has an option that can make filtering for a specific process more efficient. Using this the work of looking for matching processes can be made neater:
<?php
/*
Return an array of the pids of the processes that are running for the specific command
e.g.
returnPids('myprocess.php');
*/
function returnPids($command) {
exec("ps -C $command -o pid=",$pids);
foreach ($pids as $key=>$value) $pids[$key]=trim($value);
return $pids;
}
/*
Returns an array of the pids for processes that are like me, i.e. my program running
*/
function returnMyPids() {
return returnPids(basename($_SERVER["SCRIPT_NAME"]));
}
?>
e.g. to bomb out if I'm running already
if (count(returnMyPids())>1) exit;
gabe at fijiwebdesign dot com ¶
14 years ago
Based on what james at voodoo dot co dot uk said, but modified for CLI scripts (ie: there is no $_SERVER).
<?php
/**
* Check for a current process by filename
* @param $file[optional] Filename
* @return Boolean
*/
function processExists($file = false) {
$exists = false;
$file = $file ? $file : __FILE__;
// Check if file is in process list
exec("ps -C $file -o pid=", $pids);
if (count($pids) > 1) {
$exists = true;
}
return $exists;
}
?>
