Closed
Description
Symfony version(s) affected: 5.2.*
Description
Using nested cache contracts can cause deadlock between processes
How to reproduce
test-deadlock.php:
#!/usr/bin/env php
<?php
require __DIR__.'/vendor/autoload.php';
use Symfony\Component\Console\Application;
use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputArgument;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;
use Symfony\Component\Cache\Adapter\MemcachedAdapter;
use Symfony\Contracts\Cache\ItemInterface;
class TestCommand extends Command {
protected static $defaultName = 'test' ;
private $keys = [
'a' => ["abc_5", "def_4"],
'b' => ["fgh_17", "ijk_21"],
];
public function __construct() {
$this->cache = new MemcachedAdapter(MemcachedAdapter::createConnection('memcached://localhost'));
parent::__construct();
}
protected function configure() {
$this->addArgument('key_set', InputArgument::REQUIRED);
}
public function execute(InputInterface $input, OutputInterface $output) {
$key_set = $input->getArgument('key_set');
$value = $this->cache->get($this->keys[$key_set][0], function (ItemInterface $item) use ($key_set) {
sleep(10);
$value2 = $this->cache->get($this->keys[$key_set][1], function (ItemInterface $item) {
sleep(10);
$item->expiresAfter(1);
return 1;
});
$item->expiresAfter(1);
return 1;
});
$output->writeln("All done");
return 0;
}
}
$app = new Application();
$app->add(new TestCommand());
$app->run();composer.json:
{
"require": {
"symfony/console": "5.2.*",
"symfony/framework-bundle": "5.2.*"
}
}
memcached daemon should be running on localhost
run
composer install
if you then run the scripts sequentially,
php test-deadlock.php test a
php test-deadlock.php test b
then they exit correctly, after 20 seconds each
But if run them in parallel in different terminals, they will never finish.
If we look at the locks when the scripts are running, we will see something like this:
$ lslocks | grep php
php 32014 FLOCK 21.6K READ* 0 0 0 /.../vendor/symfony/cache/Adapter/PdoAdapter.php
php 32018 FLOCK 21.6K WRITE 0 0 0 /.../vendor/symfony/cache/Adapter/PdoAdapter.php
php 32018 FLOCK 1.9K READ* 0 0 0 /.../vendor/symfony/cache/Adapter/Psr16Adapter.php
php 32014 FLOCK 1.9K WRITE 0 0 0 /.../vendor/symfony/cache/Adapter/Psr16Adapter.php
Possible Solution
Please make using flock() in cache contract optional, or add to the documentation that using nested cache contracts is dangerous.
Additional context