CR 8005604: HPROF should report the actual instance size

[Aleksey Shipilev]

Hi guys,

This issue popped out (again?) in the course of @Contended work, which
does the padding around fields in some corner cases. HPROF just iterates
the fields to deduce the instance size, which can give a terribly wrong
instance size estimate.

I have filed CR 8005604 to track this.

FWIW, the fix appears to be very simple, we can reuse the instance size
data already available in instanceKlass, like this:

--- a/src/share/vm/services/heapDumper.cpp	Mon Dec 24 11:46:38 2012 -0800
+++ b/src/share/vm/services/heapDumper.cpp	Sat Dec 29 13:08:51 2012 +0400
@@ -772,33 +772,7 @@
 u4 DumperSupport::instance_size(Klass* k) {
   HandleMark hm;
   instanceKlassHandle ikh = instanceKlassHandle(Thread::current(), k);
-
-  int size = 0;
-
-  for (FieldStream fld(ikh, false, false); !fld.eos(); fld.next()) {
-    if (!fld.access_flags().is_static()) {
-      Symbol* sig = fld.signature();
-      switch (sig->byte_at(0)) {
-        case JVM_SIGNATURE_CLASS   :
-        case JVM_SIGNATURE_ARRAY   : size += oopSize; break;
-
-        case JVM_SIGNATURE_BYTE    :
-        case JVM_SIGNATURE_BOOLEAN : size += 1; break;
-
-        case JVM_SIGNATURE_CHAR    :
-        case JVM_SIGNATURE_SHORT   : size += 2; break;
-
-        case JVM_SIGNATURE_INT     :
-        case JVM_SIGNATURE_FLOAT   : size += 4; break;
-
-        case JVM_SIGNATURE_LONG    :
-        case JVM_SIGNATURE_DOUBLE  : size += 8; break;
-
-        default : ShouldNotReachHere();
-      }
-    }
-  }
-  return (u4)size;
+  return (u4)ikh->size_helper();
 }

 // dumps static fields of the given class


Please let me know if you have troubles with pushing this. If not, I can
get the proper due diligence to get this fixed.

Thanks,
Aleksey.