RFR 8041565: JMX ObjectName could be refactored to save memory

[Jaroslav Bachorik]

Hi Roger,

On 13.4.2015 16:07, Roger Riggs wrote:
> Hi Jaroslav,
>
> Minor comments:
>
> 1488+:  In forms like:
>
>   _pattern_flag &= (~PROPLIST_PATTERN & 0xff);"
>
> The &0xff seems unnecessary since the store is to a byte field.

Fixed: http://cr.openjdk.java.net/~jbachorik/8041565/webrev.01

>
> 1644:  the ? and : operators should be surrounded by spaces.
>
> There are other style issues, such as then statements on the same line
> as the 'if' but that
> may be beyond the scope of this change.

I know but these style issue have been around since the file was first 
committed. I didn't address them because it didn't feel right to mix 
style changes with the actual functionality.

Cheers,

-JB-

>
> Otherwise looks fine  (as a 9 reviewer, but not specifically a
> serviceability reviewer).
>
> Thanks, Roger
>
>
> On 4/13/2015 5:43 AM, Jaroslav Bachorik wrote:
>> Please, review the following change
>>
>> Issue : https://bugs.openjdk.java.net/browse/JDK-8041565
>> Webrev: http://cr.openjdk.java.net/~jbachorik/8041565/webrev.00
>>
>> In situations when there are 10s of thousands ObjectNname instances
>> around (enterprise setups etc.) the 3 separate internal boolean fields
>> can lead to a noticeable memory waste. Adding insult to the injury,
>> with the current field layout it is necessary to align the instances
>> by 4 bytes.
>>
>> When using JOL (http://openjdk.java.net/projects/code-tools/jol/) to
>> inspect the object layout we can see this:
>>
>> Before optimization (JDK8u40):
>> ---
>> javax.management.ObjectName object internals:
>> OFFSET SIZE TYPE DESCRIPTION VALUE
>>       0 12 (object header)| N/A
>>      12 4 int ObjectName._domain_length N/A
>>      16 1 boolean ObjectName._domain_pattern N/A
>>      17 1 boolean ObjectName._property_list_pattern N/A
>>      18 1 boolean ObjectName._property_value_pattern N/A
>>      19 1 (alignment/padding gap) N/A
>>      20 4 String ObjectName._canonicalName N/A
>>      24 4 Property[] ObjectName._kp_array N/A
>>      28 4 Property[] ObjectName._ca_array N/A
>>      32 4 Map ObjectName._propertyList N/A
>>      36 4 (loss due to the next object alignment)
>> Instance size: 40 bytes (estimated, the sample instance is not available)
>> Space losses: 1 bytes internal + 4 bytes external = 5 bytes total
>> {noformat}
>>
>> After optimization (JDK9 internal build):
>> ---
>>
>> javax.management.ObjectName object internals:
>>  OFFSET SIZE TYPE DESCRIPTION VALUE
>>       0 12 (object header) N/A
>>      12 2 short ObjectName._domain_length N/A
>>      14 1 byte ObjectName._pattern_flag N/A
>>      15 1 (alignment/padding gap) N/A
>>      16 4 String ObjectName._canonicalName N/A
>>      20 4 Property[] ObjectName._kp_array N/A
>>      24 4 Property[] ObjectName._ca_array N/A
>>      28 4 Map ObjectName._propertyList N/A
>> Instance size: 32 bytes (estimated, the sample instance is not available)
>> Space losses: 1 bytes internal + 0 bytes external = 1 bytes total
>>
>>
>> After optimization we can save 8 bytes per instance which can
>> translate to very interesting numbers on large installations.
>>
>>
>> To achieve this the domain name length is set to be *short* instead of
>> *int* and the three booleans kept for the performance purposes are
>> encoded into one byte value (as proposed by the reporter,
>> Jean-Francois Denise).
>>
>> All the regression and JCK tests are passing after this change.
>>
>>
>> Thanks,
>>
>> -JB-
>