smarter marking

Sun Dec 12 13:26:00 GMT 1999

It looks as though we're unconditionally marking every object's Class
object. The code for marking classes contains 5 loops. It seems like
a good idea to only mark them if they haven't been marked before.
This seems possible with a minor change to the gc's interface. I
haven't tried this yet. I just thought I'd see what people think
first.
Index: boehm-gc/gc_mark.h
===================================================================
RCS file: /cvs/java/libgcj/boehm-gc/gc_mark.h,v
retrieving revision 1.3
diff -u -r1.3 gc_mark.h

--- gc_mark.h	1999年11月01日 23:15:51	1.3
+++ gc_mark.h	1999年12月12日 21:07:44
@@ -139,9 +139,8 @@
 
 /* Push the contents of current onto the mark stack if it is a valid	*/
 /* ptr to a currently unmarked object. Mark it.			*/
-/* If we assumed a standard-conforming compiler, we could probably	*/
-/* generate the exit_label transparently.				*/
-# define PUSH_CONTENTS(current, mark_stack_top, mark_stack_limit, \
+/* Jump to exit_label if we're not marking an object. */
+# define PUSH_CONTENTS_WITH_EXIT(current, mark_stack_top, mark_stack_limit, \
 		 source, exit_label) \
 { \
 register int displ; /* Displacement in block; first bytes, then words */ \
@@ -177,6 +176,17 @@
 } \
 PUSH_OBJ(((word *)(HBLKPTR(current)) + displ), hhdr, \
 	 mark_stack_top, mark_stack_limit) \
+}
+
+/* Push the contents of current onto the mark stack if it is a valid	*/
+/* ptr to a currently unmarked object. Mark it.			*/
+/* If we assumed a standard-conforming compiler, we could probably	*/
+/* generate the exit_label transparently.				*/
+# define PUSH_CONTENTS(current, mark_stack_top, mark_stack_limit, \
+		 source, exit_label) \
+{ \
+ PUSH_CONTENTS_WITH_EXIT(current, mark_stack_top, mark_stack_limit, \
+ source, exit_label); \
 exit_label: ; \
 }
 
Index: libjava/boehm.cc
===================================================================
RCS file: /cvs/java/libgcj/libjava/boehm.cc,v
retrieving revision 1.11
diff -u -r1.11 boehm.cc
--- boehm.cc	1999年11月05日 17:34:32	1.11
+++ boehm.cc	1999年12月12日 21:07:44
@@ -91,9 +91,12 @@
 // Every object has a sync_info pointer.
 word w = (word) obj->sync_info;
 MAYBE_MARK (w, mark_stack_ptr, mark_stack_limit, obj, o1label);
- // Mark the object's class.
- w = (word) klass;
- MAYBE_MARK (w, mark_stack_ptr, mark_stack_limit, obj, o2label);
+ // Mark the object's class. Jump to the `done' label if it's already
+ // been marked.
+ if ((ptr_t) (klass) >= GC_least_plausible_heap_addr
+ && (ptr_t) (klass) <= GC_greatest_plausible_heap_addr)
+ PUSH_CONTENTS_WITH_EXIT (klass, mark_stack_ptr, 
+			 mark_stack_limit, obj, done)
 
 if (klass == &ClassClass)
 {
@@ -262,6 +265,7 @@
 	}
 }
 
+ done:
 return mark_stack_ptr;
 }
 
