Improved effectiveness from a real time LISP garbage collector

Abstract

i n h e r e n t to r e a l -t i m e g a r b a g e c o l l e c t o r s , and g i v e s o m e e v i d e n c e t h a t the p r o p o s e d a l g o r i t h m t e n d s to r e d u c e t h e s e p r o b l e m s . In a v i r t u a l m e m o r y i m p l e m e n t a t i o n , the a l g o r i t h m r e s t r u c t u r e s the c e l l s t o r a g e a r e a m o r e c o m p a c t l y , t h u s r e d u c i n g w o r k i n g sets. T h e a l g o r i t h m a l s o m a y p r o v i d e a m o r e g a r b a g e -f r e e s t o r a g e a r e a at the end of the c o l l e c t i o n c y c l e , a l t h o u g h t h i s c l a i m r e a l l y m u s t a w a i t e m p i r i c a l v e r i f i c a t i o n . G a r b a q~ c o l l e c t i o n L i s t p r o c e s s i n g s y s t e m s c o m p r i s e t w o r e l a t e d p r o c e s s e s . T h e m u t a t o r a l l o c a t e s c e l l s f r o m f r e e s t o r a g e and l i n k s t h e m t o g e t h e r to f o r m d a t a s t r u c t u r e s r e p r e s e n t i n g the c o m p u t a t i o n u n d e r w a y . W h e n the m u t a t o r d r o p s a d a t a s t r u c t u r e it no l o n g e r n e e d s , the u n d e r l y i n g c e l l s r e m a i n in the s y s t e m but are no l o n g e r a c c e s s i b l e . In o r d e r to p r e v e n t the m u t a t o r f r o m r u n n i n g out of c e l l s to a l l o c a t e and t h u s b l o c k i n g c o m p u t a t i o n , a c o l l e c t o r p r o c e s s g a t h e r s the i n a c c e s s i b l e or g a r b a g e c e l l s and r e t u r n s t h e m to f r e e s t o r a g e for r e u s e by the m u t a t o r . A n u m b e r of c o l l e c t o r a l g o r i t h m s h a v e b e e n p r o p o s e d w i t h a v a r i e t y of p e r f o r m a n c e o b j e c t i v e s . { C o h e n 8 1 ] p r o v i d e s a r e c e n t s u r v e y of g a r b a g e c o l l e c t o r s . s y s t e m . In o r d e r to m e e t r e a l -t i m e c o n s t r a i n t s , [ B a k e r 7 8 ] d i s t r i b u t e s the c o p y i n g f u n c t i o n a m o n g the m u t a t o r ' s p r i m i t i v e s . For e a c h c e l l the m u t a t o r a l l o c a t e s , it m u s t c o p y a n u m b e r of c e l l s b o u n d e d by a c o n s t a n t , k By c a r e f u l l y c h o o s i n g k, o n e c a n be a s s u r e d t h a t the m u t a t o r w i l l not run o u t of c e l l s to a l l o c a t e . M o r e o v e r , the m u t a t o r ' s p r i m i t i v e o p e r a t o r s h a v e w e l l d e f i n e d b o u n d s on t h e i r e x e c u t i o n t i m e s . T h e t r i c k is in m a i n t a i n i n g the c o n s i s t e n c y of the d a t a s t r u c t u r e s as the c o l l e c t o r c o p i e s t h e m and the m u t a t o r a l t e r s them. T h i s is a c c o m p l i s h e d by g i v i n g the m u t a t o r the i m p r e s s i o n t h a t g a r b a g e c o l l e c t i o n has c o m p l e t e d and t h a t it is w o r k i n g in the n e w s e m i s p a c e , a l t h o u g h c o p y i n g is in f a c t s t i l l g o i n g on. T h e m u t a t o r ' s a c c e s s to the d a t a s t r u c t u r e s is t h ...

A new memory allocation method for shared memory multiprocessors with large virtual address space

“…When this technique is used with applications requiring large heaps, the time used for collecting garbage is relatively small. This technique is widely used by many generational garbage collector implementations [9][10][11], as well as by many real-time and parallel garbage collector implementations [8,12,13]. Our method can be used in conjunction with all these scavenging garbage collectors.…”

Recovery using virtual memory

“…Several authors [6,201 have suggested that copying garbage collection can be used to increase the locality of refence in virtual memory for the objects it copies. The copying algorithm as presented in this chapter traverses and copies the graph of accessible objects in a breadth-first fashion.…”