That's unfortunate. Can you steal a bit in one of the int fields? E.g. lastAnnotationsRedefinedCount surely doesn't need the full range right? :)
Sent from my phone On Jan 25, 2013 11:02 AM, "Peter Levart" <peter.lev...@gmail.com> wrote: > On 01/25/2013 06:35 AM, David Holmes wrote: > >> On 25/01/2013 2:36 AM, Peter Levart wrote: >> >>> On 01/24/2013 04:45 PM, Peter Levart wrote: >>> >>>> >>>>> Is there really no existing alignment gap in j.l.Class layout that a >>>>> boolean can slide into? >>>>> >>>>> There might be, I will check. >>>> >>> All instance fields in j.l.Class are either references or ints. >>> >> >> Instance are also 8-byte aligned though so does that leave any slop where >> an extra field would not make an actual difference. (I should know the >> answer to that after the ReflectionData changes but don't recall.) >> >> Note: I have not looked at this, just considering the "add a field" >> aspect of it. >> >> David >> > > Here's what the Unsafe reports about current layout of j.l.Class > (ReflectionData changes already taken into account): > > 32 bit pointers: > > java.lang.Class instance field offsets: > > Field Type Field Name Offset > ---------- ---------- ------ > Constructor cachedConstructor 12 > Class newInstanceCallerCache 16 > String name 20 > SoftReference reflectionData 24 > ClassRepository genericInfo 28 > Object[] enumConstants 32 > Map enumConstantDirectory 36 > Map annotations 40 > Map declaredAnnotations 44 > AnnotationType annotationType 48 > ClassValueMap classValueMap 52 > int classRedefinedCount 80 > int lastAnnotationsRedefinedCount 84 > > java.lang.String static field offsets: > > Field Type Field Name Offset > ---------- ---------- ------ > ObjectStreamField[] serialPersistentFields 96 > Comparator CASE_INSENSITIVE_ORDER 100 > long serialVersionUID 104 > int HASHING_SEED 112 > > > 64 bit pointers: > > java.lang.Class instance field offsets: > > Field Type Field Name Offset > ---------- ---------- ------ > Constructor cachedConstructor 16 > Class newInstanceCallerCache 24 > String name 32 > SoftReference reflectionData 40 > ClassRepository genericInfo 48 > Object[] enumConstants 56 > Map enumConstantDirectory 64 > Map annotations 72 > Map declaredAnnotations 80 > AnnotationType annotationType 88 > ClassValueMap classValueMap 96 > int classRedefinedCount 128 > int lastAnnotationsRedefinedCount 132 > > java.lang.String static field offsets: > > Field Type Field Name Offset > ---------- ---------- ------ > ObjectStreamField[] serialPersistentFields 144 > Comparator CASE_INSENSITIVE_ORDER 152 > long serialVersionUID 160 > int HASHING_SEED 168 > > > If I add a boolean instance field "isProxy" to j.l.Class the report > changes to: > > 32 bit pointers: > > java.lang.Class instance field offsets: > > Field Type Field Name Offset > ---------- ---------- ------ > Constructor cachedConstructor 12 > Class newInstanceCallerCache 16 > String name 20 > SoftReference reflectionData 24 > ClassRepository genericInfo 28 > Object[] enumConstants 32 > Map enumConstantDirectory 36 > Map annotations 40 > Map declaredAnnotations 44 > AnnotationType annotationType 48 > ClassValueMap classValueMap 52 > int classRedefinedCount 80 > int lastAnnotationsRedefinedCount 84 > boolean isProxy 96 > > java.lang.String static field offsets: > > Field Type Field Name Offset > ---------- ---------- ------ > ObjectStreamField[] serialPersistentFields 104 > Comparator CASE_INSENSITIVE_ORDER 108 > long serialVersionUID 112 > int HASHING_SEED 120 > > > 64 bit pointers: > > java.lang.Class instance field offsets: > > Field Type Field Name Offset > ---------- ---------- ------ > Constructor cachedConstructor 16 > Class newInstanceCallerCache 24 > String name 32 > SoftReference reflectionData 40 > ClassRepository genericInfo 48 > Object[] enumConstants 56 > Map enumConstantDirectory 64 > Map annotations 72 > Map declaredAnnotations 80 > AnnotationType annotationType 88 > ClassValueMap classValueMap 96 > int classRedefinedCount 128 > int lastAnnotationsRedefinedCount 132 > boolean isProxy 144 > > java.lang.String static field offsets: > > Field Type Field Name Offset > ---------- ---------- ------ > ObjectStreamField[] serialPersistentFields 152 > Comparator CASE_INSENSITIVE_ORDER 160 > long serialVersionUID 168 > int HASHING_SEED 176 > > > ...so it seems that in both cases, adding a boolean to j.l.Class wastes 8 > bytes per Class object :-( > > > Regards, Peter > > >
