lockable_trait.rst

Prevent Multiple Executions of a Console Command

A simple but effective way to prevent multiple executions of the same command in a single server is to use locks. The :doc:`Lock component </components/lock>` provides multiple classes to create locks based on the filesystem (:ref:`FlockStore <lock-store-flock>`), shared memory (:ref:`SemaphoreStore <lock-store-semaphore>`) and even databases and Redis servers.

In addition, the Console component provides a PHP trait called LockableTrait that adds two convenient methods to lock and release commands:

// ...
use Symfony\Component\Console\Command\LockableTrait;

class UpdateContentsCommand extends Command
{
    use LockableTrait;

    // ...

    protected function execute(InputInterface $input, OutputInterface $output)
    {
        if (!$this->lock()) {
            $output->writeln('The command is already running in another process.');

            return 0;
        }

        // If you prefer to wait until the lock is released, use this:
        // $this->lock(null, true);

        // ...

        // if not released explicitly, Symfony releases the lock
        // automatically when the execution of the command ends
        $this->release();
    }
}