PHP cURL Timing Issue - php

Question

I have a PHP script that is used to query an API and download some JSON information / insert that information into a MySQL database, we'll call this scriptA.php. I need to run this script multiple times as minute, preferably as many times in a minute that I can without allowing two instances to run at the same exact time or with any overlap. My solution to this has been to create scriptB.php and put in on a one minute cron job. Here is the source code of scriptB.php...
function next_run()
{
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, "http://somewebsite.com/scriptA.php");
curl_exec($curl);
curl_close($curl);
unset($curl);
}
$i = 0;
$times_to_run = 7;
$function = array();
while ($i++ < $times_to_run) {
$function = next_run();
sleep(3);
}
My question at this point is to how cURL performs when used in a loop, does this code trigger scriptA.php and THEN once it has finished loading it at that point start the next cURL request? Does the 3 second sleep even make a difference or will this literally run as fast as the time it takes each cURL request to complete. My objective is to time this script and run it as many times as possible in a one minute window without two iterations of it being run at the same time. I don't want to include the sleep statement if it is not needed. I believe what happens is cURL will run each request upon finishing the last, if I am wrong is there someway that I can instruct it to do this?

Answer 1

preferably as many times in a minute that I can without allowing two instances to run at the same exact time or with any overlap. - then you shouldn't use a cronjob at all, you should use a daemon. but if you for some reason have to use a cronjob (eg, if you're on a shared webhosting platform that doesn't allow daemons), guess you could use the sleep hack to run the same code several times a minute?
* * * * * /usr/bin/php /path/to/scriptA.php
* * * * * sleep 10; /usr/bin/php /path/to/scriptA.php
* * * * * sleep 20; /usr/bin/php /path/to/scriptA.php
* * * * * sleep 30; /usr/bin/php /path/to/scriptA.php
* * * * * sleep 40; /usr/bin/php /path/to/scriptA.php
* * * * * sleep 50; /usr/bin/php /path/to/scriptA.php
should make it execute every 10 seconds.
as for making sure it doesn't run in paralell if the previous execution hasn't finished yet, add this to the start of scriptA
call_user_func ( function () {
static $lock;
$lock = fopen ( __FILE__, "rb" );
if (! flock ( $lock, LOCK_EX | LOCK_NB )) {
// failed to get a lock, probably means another instance is already running
die ();
}
register_shutdown_function ( function () use (&$lock) {
flock ( $lock, LOCK_UN );
} );
} );
and it will just die() if another instance of scriptA is already running. however, if you want it to wait for the previous execution to finish, instead of just exiting, remove LOCK_NB... but that could be dangerous, if every, or even just a majority of the executions use more than 10 seconds, you'll have more and more processes waiting for the previous execution to finish, until you run out of ram.
as for your curl questions,
My question at this point is to how cURL performs when used in a loop, does this code trigger scriptA.php and THEN once it has finished loading it at that point start the next cURL request, that is correct, curl waits until the page has completely loaded, usually meaning the entire scriptA has completed. (you can tell scriptA to finish the pageload prematurely with the fastcgi_finish_request() function if you really want, but that's unusual)
Does the 3 second sleep even make a difference or will this literally run as fast as the time it takes each cURL request to complete - yes, the sleep will make the loop 3 seconds slower per iteration.
My objective is to time this script and run it as many times as possible in a one minute window without two iterations of it being run at the same time - then make it a daemon that never exits, rather than a cronjob.
I don't want to include the sleep statement if it is not needed. - it's not needed.
I believe what happens is cURL will run each request upon finishing the last - this is correct.

Answer 2

I need to run this script multiple times as minute, preferably as many times in a minute that I can without allowing two instances to run
Your in luck as I wrote a class to handle just such a thing. You can find it on my github here
https://github.com/ArtisticPhoenix/MISC/blob/master/ProcLock.php
I'll also copy the full code at the end of this post.
The basic idea is to create a file, I will call it afile.lock for this example. In this file is recorded the PID, or the process ID of the current process that is ran by cron. Then when cron attempts to run the process again, it checks this lock file and sees if there is a PHP process running that is using this PID.
if there is it updates the modified time of the file (and throws an exception)
if there is not then you are free to create a new instance of the "worker".
As a bonus th modified time of the lock file can be used by the script (whose PID we are tracking) as a way of shutting down in the event the file is not updated, so for example: if cron is stopped, or if the lock file is manually deleted you can set in in such a way that the running script will detect this and self destruct.
So not only can you keep multiple instances from running, you can tell the current instance to die if cron is turned off.
The basic usage is as follows. In the cron file that starts up the "worker"
//define a lock file (this is actually optional)
ProcLock::setLockFile(__DIR__.'/afile.lock');
try{
//if you didn't set a lock file you can pass it in with this method call
ProcLock::lock();
//execute your process
}catch(\Exception $e){
if($e->getCode() == ProcLock::ALREADY_LOCKED){
//just exit or what have you
}else{
//some other exception happened.
}
}
It's basically that easy.
Then in the running process you can every so often check (for example if you have a loop that runs something)
$expires = 90; //1 1/2 minute (you may need a bit of fudge time)
foreach($something as $a=>$b){
$lastAccess = ProcLock::getLastAccess()
if(false == $lastAccess || $lastAccess + $expires < time()){
//if last access is false (no lock file)
//or last access + expiration, is less then the current time
//log something like killed by lock timeout
exit();
}
}
Basically what this says is that either the lock file was deleted wile the process was running, or cron failed to update it before the expiration time. So here we are giving it 90 seconds and cron should be updating the lock file every 60 seconds. As I said the lock file is updated automatically if it's found when calling lock(), which calls canLock() which if it returns true meaning we can lock the process because its not currently locked, then it runs touch($lockfile) which updates the mtime (modified time).
Obviously you can only self kill the process in this way if it is actively checking the access and expiration times.
This script is designed to work both on windows and linux. On windows under certain circumstances the lock file won't properly be deleted (sometimes when hitting ctrl+c in the CMD window), however I have taken great pains to make sure this does not happen, so the class file contains a custom register_shutdown_function that runs when the PHP script ends.
When running something using the ProcLoc in the browser please note that the process id will always be the same no matter the tab its ran in. So if you open one tab that is Process locked, then open another tab, the process locker will see it as the same process and allow it to lock again. To properly run it in a browser and test the locking it must be done using two separate browsers such as crome and firefox. It's not really intended to be ran in the browser but this is one quirk I noticed.
One last note this class is completely static, as you can have only one Process ID per process that is running, which should be obvious.
The tricky parts are
making sure the lock file is disposed of in the event of even critical PHP failures
making sure another process didn't pick up the pid number when it was freed from PHP. This can be done with relative accuracy, in that we can tell if a PHP process is using it, and if so we assume its the process we need, there is much less chance a re-used PID would show up for another process very quickly, even less that it would be another PHP process
making all this work on both Linux and Windows
Lucky for you I have already invested sufficient time in this to do all these things, this is a more generic version of an original lock script I made for my job that we have used in this way successfully for 3 years in maintaining control over various synchronous cron jobs, everything from sFTP upload scanning, expired file clean up to RabbitMq message workers that run for an indefinite period of time.
In anycase here is the full code, enjoy.
<?php
/*
(c) 2017 ArtisticPhoenix
For license information please view the LICENSE file included with this source code GPL3.0.
Proccess Locker
==================================================================
This is a pseudo implementation of mutex since php does not have
any thread synchronization objects
This class uses files to provide locking functionality.
Lock will be released in following cases
1 - user calls unlock
2 - when this lock object gets deleted
3 - when request or script ends
4 - when pid of lock does not match self::$_pid
==================================================================
Only one Lock per Process!
-note- when running in a browser typically all tabs will have the same PID
so the locking will not be able to tell if it's the same process, to get
around this run in CLI, or use 2 diffrent browsers, so the PID numbers are diffrent.
This class is static for the simple fact that locking is done per-proces, so there is no need
to ever have duplate ProcLocks within the same process
---------------------------------------------------------------
*/
final class {
/**
* exception code numbers
* #var int
*/
const DIRECTORY_NOT_FOUND = 2000;
const LOCK_FIRST = 2001;
const FAILED_TO_UNLOCK = 2002;
const FAILED_TO_LOCK = 2003;
const ALREADY_LOCKED = 2004;
const UNKNOWN_PID = 2005;
const PROC_UNKNOWN_PID = 2006;
/**
* process _key
* #var string
*/
protected static $_lockFile;
/**
*
* #var int
*/
protected static $_pid;
/**
* No construction allowed
*/
private function __construct(){}
/**
* No clones allowed
*/
private function __clone(){}
/**
* globaly sets the lock file
* #param string $lockFile
*/
public static function setLockFile( $lockFile ){
$dir = dirname( $lockFile );
if( !is_dir( dirname( $lockFile ))){
throw new Exception("Directory {$dir} not found", self::DIRECTORY_NOT_FOUND); //pid directroy invalid
}
self::$_lockFile = $lockFile;
}
/**
* return global lockfile
*/
public static function getLockFile() {
return ( self::$_lockFile ) ? self::$_lockFile : false;
}
/**
* safe check for local or global lock file
*/
protected static function _chk_lock_file( $lockFile = null ){
if( !$lockFile && !self::$_lockFile ){
throw new Exception("Lock first", self::LOCK_FIRST); //
}elseif( $lockFile ){
return $lockFile;
}else{
return self::$_lockFile;
}
}
/**
*
* #param string $lockFile
*/
public static function unlock( $lockFile = null ){
if( !self::$_pid ){
//no pid stored - not locked for this process
return;
}
$lockFile = self::_chk_lock_file($lockFile);
if(!file_exists($lockFile) || unlink($lockFile)){
return true;
}else{
throw new Exception("Failed to unlock {$lockFile}", self::FAILED_TO_UNLOCK ); //no lock file exists to unlock or no permissions to delete file
}
}
/**
*
* #param string $lockFile
*/
public static function lock( $lockFile = null ){
$lockFile = self::_chk_lock_file($lockFile);
if( self::canLock( $lockFile )){
self::$_pid = getmypid();
if(!file_put_contents($lockFile, self::$_pid ) ){
throw new Exception("Failed to lock {$lockFile}", self::FAILED_TO_LOCK ); //no permission to create pid file
}
}else{
throw new Exception('Process is already running[ '.$lockFile.' ]', self::ALREADY_LOCKED );//there is a process running with this pid
}
}
/**
*
* #param string $lockFile
*/
public static function getPidFromLockFile( $lockFile = null ){
$lockFile = self::_chk_lock_file($lockFile);
if(!file_exists($lockFile) || !is_file($lockFile)){
return false;
}
$pid = file_get_contents($lockFile);
return intval(trim($pid));
}
/**
*
* #return number
*/
public static function getMyPid(){
return ( self::$_pid ) ? self::$_pid : false;
}
/**
*
* #param string $lockFile
* #param string $myPid
* #throws Exception
*/
public static function validatePid($lockFile = null, $myPid = false ){
$lockFile = self::_chk_lock_file($lockFile);
if( !self::$_pid && !$myPid ){
throw new Exception('no pid supplied', self::UNKNOWN_PID ); //no stored or injected pid number
}elseif( !$myPid ){
$myPid = self::$_pid;
}
return ( $myPid == self::getPidFromLockFile( $lockFile ));
}
/**
* update the mtime of lock file
* #param string $lockFile
*/
public static function canLock( $lockFile = null){
if( self::$_pid ){
throw new Exception("Process was already locked", self::ALREADY_LOCKED ); //process was already locked - call this only before locking
}
$lockFile = self::_chk_lock_file($lockFile);
$pid = self::getPidFromLockFile( $lockFile );
if( !$pid ){
//if there is a not a pid then there is no lock file and it's ok to lock it
return true;
}
//validate the pid in the existing file
$valid = self::_validateProcess($pid);
if( !$valid ){
//if it's not valid - delete the lock file
if(unlink($lockFile)){
return true;
}else{
throw new Exception("Failed to unlock {$lockFile}", self::FAILED_TO_UNLOCK ); //no lock file exists to unlock or no permissions to delete file
}
}
//if there was a valid process running return false, we cannot lock it.
//update the lock files mTime - this is usefull for a heartbeat, a periodic keepalive script.
touch($lockFile);
return false;
}
/**
*
* #param string $lockFile
*/
public static function getLastAccess( $lockFile = null ){
$lockFile = self::_chk_lock_file($lockFile);
clearstatcache( $lockFile );
if( file_exists( $lockFile )){
return filemtime( $lockFile );
}
return false;
}
/**
*
* #param int $pid
*/
protected static function _validateProcess( $pid ){
$task = false;
$pid = intval($pid);
if(stripos(php_uname('s'), 'win') > -1){
$task = shell_exec("tasklist /fi \"PID eq {$pid}\"");
/*
'INFO: No tasks are running which match the specified criteria.
'
*/
/*
'
Image Name PID Session Name Session# Mem Usage
========================= ======== ================ =========== ============
php.exe 5064 Console 1 64,516 K
'
*/
}else{
$cmd = "ps ".intval($pid);
$task = shell_exec($cmd);
/*
' PID TTY STAT TIME COMMAND
'
*/
}
//print_rr( $task );
if($task){
return ( preg_match('/php|httpd/', $task) ) ? true : false;
}
throw new Exception("pid detection failed {$pid}", self::PROC_UNKNOWN_PID); //failed to parse the pid look up results
//this has been tested on CentOs 5,6,7 and windows 7 and 10
}
/**
* destroy a lock ( safe unlock )
*/
public static function destroy($lockFile = null){
try{
$lockFile = self::_chk_lock_file($lockFile);
self::unlock( $lockFile );
}catch( Exception $e ){
//ignore errors here - this called from distruction so we dont care if it fails or succeeds
//generally a new process will be able to tell if the pid is still in use so
//this is just a cleanup process
}
}
}
/*
* register our shutdown handler - if the script dies unlock the lock
* this is superior to __destruct(), because the shutdown handler runs even in situation where PHP exhausts all memory
*/
register_shutdown_function(array('\\Lib\\Queue\\ProcLock',"destroy"));