What is a Lock?

File locking is a mechanism that restricts access to a computer file by allowing only one user or process access at any specific time. This mechanism was introduced a few decades ago for mainframes, but continues being useful for modern applications.

Symfony provides a LockHelper to help you use locks in your project.

Usage

A lock can be used, for example, to allow only one instance of a command to run.

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use Symfony\Component\Filesystem\LockHandler;

$lockHandler = new LockHandler('hello.lock');
if (!$lockHandler->lock()) {
    // the resource "hello" is already locked by another process

    return 0;
}

The first argument of the constructor is a string that it will use as part of the name of the file used to create the lock on the local filesystem. A best practice for Symfony commands is to use the command name, such as acme:my-command. LockHandler sanitizes the contents of the string before creating the file, so you can pass any value for this argument.

By default, the lock will be created in the temporary directory, but you can optionally select the directory where locks are created by passing it as the second argument of the constructor.

The lock() method tries to acquire the lock. If the lock is acquired, the method returns true, false otherwise. If the lock method is called several times on the same instance it will always return true if the lock was acquired on the first call.

You can pass an optional blocking argument as the first argument to the lock() method, which defaults to false. If this is set to true, your PHP code will wait indefinitely until the lock is released by another process.

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use Symfony\Component\Filesystem\LockHandler;

 if (!(new LockHandler('hello.lock'))->lock()) {
    // the resource "hello" is already locked by another process

    return 0;
}