question: public static String obtainLock ( EntityManager em , long expiration , long type , String note ) { EntityTransaction tx = null ; try { long now = System . currentTimeMillis ( ) ; tx = em . getTransaction ( ) ; tx . begin ( ) ; GlobalInterlock lock = _findAndRefreshLock ( em , type ) ; if ( lock != null && now - lock . lockTime > expiration ) { em . remove ( lock ) ; em . flush ( ) ; } tx . commit ( ) ; } catch ( Exception ex ) { LOGGER . warn ( "An error occurred trying to refresh the type {} lock: {}" , type , ex . getMessage ( ) ) ; LOGGER . debug ( ex . getMessage ( ) , ex ) ; if ( tx != null && tx . isActive ( ) ) { tx . rollback ( ) ; } } try { tx = em . getTransaction ( ) ; tx . begin ( ) ; GlobalInterlock lock = em . merge ( new GlobalInterlock ( type , note ) ) ; em . flush ( ) ; tx . commit ( ) ; return Long . toHexString ( lock . lockTime ) ; } catch ( Exception ex ) { throw new GlobalInterlockException ( "Could not obtain " + type + " lock" , ex ) ; } finally { if ( tx != null && tx . isActive ( ) ) { tx . rollback ( ) ; } } }
target:  Obtains a global lock of a given type.