Gracefully stop the PHP process before max execution time is reached

[brefphp]

Gracefully stop the PHP process before max execution time is reached

[t-geindre]

I made a simple POC to validate my idea.

Here a simple PHP script which handle signals and runs forever:

<?php
declare(ticks = 1);

class SigtermException extends \Exception {}

pcntl_signal(SIGTERM, function () {
	throw new SigtermException('SIGTERM received');
});


set_exception_handler(function ($exception) {
	// Log exception as usual
	echo "Exception thrown: " , $exception->getMessage(), "\n";
	// If it's a Sigterm one, stop execution
	if ($exception instanceof SigtermException) {
		exit(1);
	}
});


for(;;){
	echo "Running\n";
	usleep(100000);
}

And here is the javascript handler which runs the PHP script:

const spawn = require('child_process').spawn;

var script = spawn('php', ['test.php']);
var timeoutHandler = setTimeout(() => script.kill('SIGTERM'), 2000);

script.on('close', (code) => {
	console.log('Process closed with code: ' + code);
	clearTimeout(timeoutHandler);
});

script.stdout.on('data', function(data) {
    console.log(data.toString());
});

script.stderr.on('data', function(data) {
    console.log('[STDERR] ' + data.toString());
});

And finally the execution output:

$ nodejs handler.js
Running

Running

[...]

Running

Exception thrown: SIGTERM received

Process closed with code: 1

So it seems to be working as expected and would allows us to to gracefully shut down the PHP process before the lambda shuts down.

[t-geindre]

A simple solution is the following:

pcntl_async_signals(true);
pcntl_signal(SIGALRM, function () {
     throw new \RuntimeException('Maximum execution time reached');
});
pcntl_alarm(2); // a SIGALRM will be triggered after 2 seconds

This could work and wouldn't require any modification in Bref.

[mnapoli]

Yes that is really interesting!

Just to be the devil's advocate: when not using AWS lambda (i.e. Apache/Nginx setup) there is a time limit too and there is the same problem right? So in a way my opinion is that since it's not a new constraint specific to lambdas, it's not critical to offer a solution for this.

However if it's easy and doesn't impact a lot the architecture of Bref then why not! And since we control the PHP binary we can make sure pcntl is available.

[t-geindre]

Just to be the devil's advocate: when not using AWS lambda (i.e. Apache/Nginx setup) there is a time limit too and there is the same problem right? So in a way my opinion is that since it's not a new constraint specific to lambdas, it's not critical to offer a solution for this.

We shouldn't think as if we were working on a classic setup. On natively supported languages, AWS provides a context object which provides a method to get the remaining execution time. That's exactly why I had this idea, in other languages we can check the time left and that's not possible at the moment with PHP/Bref.

Another solution could be to give access to that context object, this could be done through socket for example.