README

Simple file based locking.

Features

• file based locking with flock()
• works on Unix-like systems as well as Windows
• supports timeout for acquiring lock
• no third-party dependencies

Install

The easiest way to install FileLock is by using composer:

$> composer require fostam/filelock

Usage

<?php

require "vendor/autoload.php";

$fl = new \Fostam\FileLock\FileLock('mylock');
if (!$fl->acquire()) {
    exit;
}

// do exclusive stuff

$fl->release();

Locking

The name of the lock is passed as first argument to the constructor:

$fl = FileLock('mylock');

Acquiring the lock is done with the acquire() method:

$fl->acquire();

It will return true on success and false if the lock is already present. If an error occurs, an exception is thrown (see below).

Optionally, a timeout in seconds can be passed:

$fl->acquire(10);

The acquire() method will try to get the lock once per second until the timeout has been reached. If the lock could not be acquired, false will be returned.

A value of 0 will immediately return false if the locking fails. This is also the default behaviour if no timeout is given.

Unlocking

Explicitly releasing the lock:

$fl->release();

The lock is also implicitly released in the desctructor of the FileLock class if still present on destruction of the object.

Lock File

The process id (PID) of the locking process is written into the lock file after acquiring the lock.

By default, the lock file is created in the system's temporary directory as returned by sys_get_temp_dir(). An alternative directory can be passed to the constructor as second parameter:

$fl = FileLock('mylock', '/var/run');

In this example, the lock file would be /var/run/mylock.lock.

If required, the full lock file name can be retrieved from the FileLock object:

$filename = $fl->getLockFileName();

If the lock file is kept in a place that is subject to periodic cleanups (e.g. /tmp on most Linux systems), it can be refreshed with the refresh() method:

$fl->refresh();

This will update the file's modification time to the current timestamp.

NOTE: To avoid race conditions, the lock file is not deleted when released.

Exceptions

All exceptions inherit the common LockFileException class.

The acquire() method might throw one of the following exceptions:

• LockFileNotOpenableException: the lock file can not be created or opened
• LockFileOperationFailedException: a file system operation on the lock file has failed
• LockFileVanishedException: the lock file has vanished after acquiring the lock

The release() method will throw the LockFileOperationFailureException exception in case the unlock file system operation fails.