AbstractSessionHandler::read

public function read($sessionId)
{
	if (!$this->validateSessionId($sessionId))
	{
		return '';
	}

	$this->sessionId = $sessionId;
	if ($this->prefetchId !== null)
	{
		$prefetchId = $this->prefetchId;
		$prefetchData = $this->prefetchData;

		$this->prefetchId = null;
		$this->prefetchData = null;

		if ($prefetchId === $this->sessionId)
		{
			return $prefetchData;
		}
	}

	if (!$this->readOnly && !$this->lock($this->sessionId))
	{
		$this->triggerLockFatalError();
	}

	return $this->processRead($sessionId);
}