Limit number of instances of Symfony Command - symfony

Question

I have a command in my Symfony app launched by Cron. I want to be able to limit the number of instances executed at the same time on my server, let's say 4 instances. I don't have any clue on how to do this. I found how to lock the command to launch the command only one time and wait for it to finish, but I don't know how to launch more than one and limit the number of instances anyway.
Do you have an idea ?

Answer 1

What you are looking for is a semaphore.
There is a LockComponent currently scheduled for 3.4 (was pulled from 3.3). It is a major improvement over the LockHandler in the FilesystemComponent.
In a pinch, you can probably pool a fixed number of locks from the LockHandler. I don't recommend it, because it uses flock on the filesystem. This limits the lock to a single server. Additionally, flock may be limited to the process scope on some systems.
<?php
use Symfony\Component\Filesystem\LockHandler;
define('LOCK_ID', 'some-identifier');
define('LOCK_MAX', 5);
$lockPool = [];
for ($i = 0; $i <= LOCK_MAX;) {
$lockHandle = sprintf('%s-%s.lock', LOCK_ID, ++$i);
$lockPool[$i] = new LockHandler($lockHandle);
}
$activeLock = null;
$lockTimeout = 60 * 1000;
$lockWaitStart = microtime(true);
while(!$activeLock) {
foreach ($lockPool as $lockHandler) {
if ($lockHandler->lock()) {
$activeLock = $lockHandler;
break 2;
}
}
if ($lockTimeout && ($lockTimeout > microtime(true) - $lockWaitStart)) {
break;
}
// Randomly wait between 0.1ms and 10ms
usleep(mt_rand(100, 10000));
}
A much better and efficient solution would be to use the semaphore extension and work some magic with ftok, shm_* and sem_*.

Answer 2

i suggest you to use a process control system as supervisor. it's pretty simple to use and you can choose how many instance of your script you start.
http://supervisord.org/

Answer 3

You could use a shared counter file which holds a counter that gets increased when the Command starts running and decreases it before it's finished.
Another solution would be checking the process list with something like this:
$processCount = exec('ps aux | grep "some part of the console command you run" | grep -v "grep" | wc -l' );
if(!empty($processCount) && $processCount >= X) {
return false;
}

Answer 4

You can create a "launcher command" executed by your cron or supervisor.
This Symfony commad can launch your instances with the process component on your server. You can also check whatever you want to check and do everything you want to do like the exec php function.