PHP Lock Handler

lock-hanlder.php

<?php

/**
 * A helper class for file locking stuff.
 * Locks obtained through this class are shared with the entire request,
 * allowing multiple objects to get their own locks on the same file
 * without deadlocking internally.
 */
class LockHandler
{
	public static function getInstance()
	{
		static $instance = null;
		if ($instance === null)
		{
			$instance = new LockHandler();
		}
		return $instance;
	}

	private $handles = array();

	/**
	 * Gets an internally shared lock on the given file.
	 * @param lockfile: The path to the file to lock.
	 *        It is recommended that this be an absolute path to avoid
	 *        attempting to lock the same file twice.
	 * @returns: The resource from opening the file, opened with file_open.
	 */
	public function lock($lockfile)
	{
		if (!isset($this->handles[$lockfile]))
		{
			$resource = file_lock($lockfile);
			$this->handles[$lockfile] = new stdClass();
			$this->handles[$lockfile]->count = 0;
			$this->handles[$lockfile]->handle = $resource;
		}
		$this->handles[$lockfile]->count++;
		return $this->handles[$lockfile]->handle;
	}

	/**
	 * Releases a lock on the given file or resource.
	 * @param resource: The path to the file to lock, or the resource from opening it.
	 *        It is recommended that this be the resource.
	 */
	public function unlock($resource)
	{
		$wrapper = null;
		$lockfile = null;

		if (is_resource($resource))
		{
			foreach ($this->handles as $path => $res)
			{
				if ($res->handle === $resource)
				{
					$wrapper = $res;
					$lockfile = $path;
					break;
				}
			}
		}
		else if (is_string($resource))
		{
			$lockfile = $resource;
			$wrapper = @$this->handles[$lockfile];
		}

		if ($wrapper === null)
		{
			throw new Exception("Cannot unlock unknown item '$resource'.", E_INTERNAL_ERROR);
		}

		$wrapper->count--;
		$ret = true;
		if ($wrapper->count === 0 && ($ret = file_unlock($wrapper->handle)))
		{
			unset($this->handles[$lockfile]);
		}
		return $ret;
	}

	/**
	 * Testing method.
	 * Returns the number of active repo hanldes.
	 * Intended to help catch potential deadlocks with other threads.
	 */
	public function handleCount()
	{
		return count($this->handles);
	}
}

test-lock-handler.php

<?php

$lh = LockHandler::getInstance();

// $testWorkPath

$file = $testWorkPath.'/bacon';

$lock1 = $lh->lock($file);
test_nonempty($lock1, 'Failed to get first lock on file!');
$lock2 = $lh->lock($file);
test_nonempty($lock2, 'Failed to get second lock on file!');

test_true($lock1 === $lock2, 'Simultaneous locks on the same file should be the same resource');
test_equal($lh->handleCount(), 1, 'Two locks on the same file should be stored as a single handle');

$lh->unlock($lock2);

test_equal($lh->handleCount(), 1, 'Releasing one lock on the file should not remove the lock completely');

$lh->unlock($file);

test_equal($lh->handleCount(), 0, 'Releasing the remaining lock on the file should remove the lock completely');

$lock3 = $lh->lock($file);

test_nonempty($lock3, 'Failed to get lock on file after closing all previous handles');
test_equal($lh->handleCount(), 1, 'Getting another lock on the file should be stored as a single handle');

$lh->unlock($file);

test_equal($lh->handleCount(), 0, 'Releasing third lock on the file should remove the lock completely');