3112	 List Processing in Real Time on a Serial Computer	 A real-time list processing system is one in which the time required by the elementary list operations e.g. CONS CAR CDR RPLACA REPLACD EQ and ATOM in LISP is bounded by a small constant. Classical implementations of list processing systems lack this property because allocating a list cell from the heap may cause a garbage collection which process requires time proportional to the heap size to finish. A real-time list processing system is presented which continuously reclaims garbage including directed cycles while linearizing and compacting the accessible cells into contiguous locations to avoid fragmenting the free storage pool. The program is small and requires no time-sharing interrupts making it suitable for microcode. Finally the system requires the same average time and not more than twice the space of a classical implementation and those space requirements can be reduced to approximately classical proportions by compact list representation. Arrays of different sizes a program stack and hash linking are simple extensions to our system and reference counting is found to be inferior for many applications. Real-time compacting garbage collection list processing virtual memory file or database management storage management storage allocation LISP CDR-coding reference counting.
