question: public void begin ( ) { Operation op = currOp . get ( ) ; if ( op != null ) { op . reentries ++ ; return ; } op = new Operation ( ) ; currOp . set ( op ) ; for ( ; ; ) { Operation prev = head . get ( ) ; op . previous ( prev ) ; if ( head . compareAndSet ( prev , op ) ) { prev . next ( op ) ; break ; } } }
target:  Begins concurrent memory operation.