I'm trying to find a safe way to prevent a cron job collision (ie. prevent it from running if another instance is already running).
Some options I've found recommend using a lock on a file.
Is that really a safe option? What would happen if the script dies for example? Will the lock remain?
Are there other ways of doing this?
I've extended the concept from zerkms to create a function that can be called from the start of a cron.
Using the Cronlocker you specify a lock name, then the name of a callback function to be called if the cron is OFF. Optionally you may give an array of parameters to pass to the callback function. There's also an optional callback function if you need to do something different if the lock is ON.
In some cases I got a few exceptions and wanted to be able to trap them, and I added a function for handling fatal exceptions, which should be added. I wanted to be able to hit the file from a browser and bypass the cronlock, so that's built in.
I found as I used this a lot there were cases where I wanted to block other crons from running while this cron is running, so I added an optional array of lockblocks, which are other lock names to block.
Then there were cases where I wanted this cron to run after other crons had finished, so there's an optional array of lockwaits, which are other lock names to wait until none of which are running.
simple example:
callback parameters and failure functions:
blocking and waiting:
class:
Should also be implemented on a common page, or built into your existing fatal error handler:
In Symfony Framework you could use the lock component symfony/lock
https://symfony.com/doc/current/console/lockable_trait.html
This sample was taken at http://php.net/flock and changed a little and this is a correct way to do what you want:
Credits:
w+
instead ofr+