Facebook Engineer?

This function is available as File\AlreadyLockedException() in Facebook's www repository.

Indicates that a lock failed, because the file is already locked

This class does not extend OS\Exception as an EWOULDBLOCK after flock($fd, LOCK_NB) is expected rather than an error; this exception is thrown when the caller has explicitly requested an exception for these cases.

Interface Synopsis

namespace HH\Lib\File;

final class AlreadyLockedException extends \Exception {...}