Proxy.isProxyClass scalability

[Vitaly Davidovich]

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.levart at 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
>
>
>