RedisLock.php

<?php
/**
 * Global Locking using Redis
 *
 */
class RedisLock {

/**
 * How long should the lock be kept active, even if the process dies
 *
 * @var integer
 */
	public static $lockTimeout = 20;

/**
 * Stores the expire time of the currently held lock
 *
 * @var int
 */
	protected static $_expire;

/**
 * Gets a lock or waits for it to become available
 *
 * @param  mixed	$key			Item to lock
 * @param  int		$timeout	Time to wait for the key (seconds)
 * @return mixed	The key
 * @throws LockException If the key is invalid
 * @throws LockTimeoutException If the lock is not acquired before the method times out
 */
	public static function get($key, $timeout = 10, $sleep = 1) {
		if (empty($key)) {
			throw new LockException('Invalid Key');
		}

		$start = time();
		$acquired = false;

		do {
			static::$_expire = static::timeout();

			if ($acquired = (static::_getRedis()->setnx("mutex:{$key}", static::$_expire))) {
				break;
			}

			if ($acquired = (static::recover($key))) {
				break;
			}

			if ($timeout === 0) {
				break;
			}

			sleep($sleep);
		} while(!is_numeric($timeout) || time() < $start + $timeout);

		if (!$acquired) {
			throw new LockTimeoutException("Timeout exceeded");
		}

		return $key;
	}

/**
 * Releases the lock
 *
 * @param  mixed	$key	Item to lock
 * @throws LockException If the key is invalid
 */
	public static function release($key) {
		if (empty($key)) {
			throw new LockException('Invalid Key');
		}

		// Only release the lock if it hasn't expired
		if (static::$_expire > time()) {
			static::_getRedis()->del("mutex:{$key}");
		}
	}

/**
 * Generates an expire time based on the current time
 *
 * @return int	timeout
 */
	protected static function timeout() {
		return (int) (time() + static::$lockTimeout + 1);
	}

/**
 * Recover an abandoned lock
 *
 * @param  mixed	$key	Item to lock
 * @return bool	Was the lock acquired?
 */
	protected static function recover($key) {
		if (($lockTimeout = static::_getRedis()->get("mutex:{$key}")) > time()) {
			return false;
		}

		$timeout = static::timeout();
		$currentTimeout = static::_getRedis()->getset("mutex:{$key}", $timeout);

		if ($currentTimeout != $lockTimeout) {
			return false;
		}

		static::$_expire = $timeout;
		return true;
	}

/**
 * Get an redis instance
 *
 * @return Redis
 */
	protected static function _getRedis() {
		return ConnectionManager::getDataSource('redis');
	}

}

class LockException extends RuntimeException {

}

class LockTimeoutException extends LockException {

}