6948538: CMS: BOT walkers can fall into object allocation and initialization cracks Summary: GC workers now recognize an intermediate transient state of blocks which are allocated but have not yet completed initialization. blk_start() calls do not attempt to determine the size of a block in the transient state, rather waiting for the block to become initialized so that it is safe to query its size. Audited and ensured the order of initialization of object fields (klass, free bit and size) to respect block state transition protocol. Also included some new assertion checking code enabled in debug mode. Reviewed-by: chrisphi, johnc, poonam

--- a/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp	Sat Aug 14 00:47:52 2010 -0700
+++ b/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp	Mon Aug 16 15:58:42 2010 -0700
@@ -1010,10 +1010,10 @@
 
   // Non-product stat counters
   NOT_PRODUCT(
-    int _numObjectsPromoted;
-    int _numWordsPromoted;
-    int _numObjectsAllocated;
-    int _numWordsAllocated;
+    size_t _numObjectsPromoted;
+    size_t _numWordsPromoted;
+    size_t _numObjectsAllocated;
+    size_t _numWordsAllocated;
   )
 
   // Used for sizing decisions