RFR 8041565: JMX ObjectName could be refactored to save memory

[Jaroslav Bachorik]

Eamonn, Daniel,

thanks for the comments.

I've updated the webrev to address them. Also, I've added a test to 
exercise the boolean flag en-/decoding in ObjectName.

http://cr.openjdk.java.net/~jbachorik/8041565/webrev.03


Cheers,

-JB-

On 4.8.2015 23:02, Daniel Fuchs wrote:
> Hi Jaroslav,
>
>   379      * This field encodes _domain_pattern, _property_list_pattern and
>   380      * _property_value_pattern booleans.
>
> If I'm not mistaken it also encodes the domain length.
>
>
>   1072         if ((l & FLAG_MASK) > 0 ) {
>
> Although it is not expected that 'l' could be negative, it might be
> better to write this test as:
>
>               if ((l & FLAG_MASK) != 0 ) {
>
> (+ I agree with Éamonn that l is not a great parameter name - nice to
> see you back  Éamonn :-)) best regards, -- daniel On 8/4/15 4:20 PM,
> Jaroslav Bachorik wrote:
>> Hi, reviving this review. On 14.4.2015 16:58, Jaroslav Bachorik wrote:
>>> On 14.4.2015 14:56, Daniel Fuchs wrote:
>>>> Hi Jaroslav, I like this change, but it does introduce an
>>>> incompatibility, so it probably needs a CCC and some release notes.
>>>> For instance, this test passes with the current version of
>>>> ObjectName: public class StringLengthTest {      final static int
>>>> smax = Short.MAX_VALUE;      final static int smore = smax + 126;
>>>>      public static void main(String[] args) throws
>>>> MalformedObjectNameException {          char[] chars = new
>>>> char[smore];          Arrays.fill(chars, 0, smax, 'a');
>>>> Arrays.fill(chars, smax, smore, 'b');
>>>> System.out.println(new ObjectName(new String(chars), "type",
>>>> "Test"));      } } I'm not sure what it will do with your changes :-)
>>> It will fail with assert (if enabled). Or truncate the domain name, I
>>> suppose.
>>>> With that in mind I believe you should consider throwing
>>>> InternalError - or IllegalArgumentException - instead of using
>>>> 'assert' statements.
>>> This would probably be better.
>>>> BTW have you run the JCK?
>>> Yes. All passed. I don't think JCK is testing for unrealistic values
>>> :) I don't see how one could come up with a domain name 32767
>>> characters long.
>> The proposed change has passed the CCC review. In case the domain name
>> is longer than Integer.MAX_VALUE/4 a MalformedObjectNameException will
>> be thrown. All the JMX tests and JCK are still passing.
>> http://cr.openjdk.java.net/~jbachorik/8041565/webrev.02 -JB-
>>> -JB-
>>>> best regards, -- daniel On 13/04/15 17:07, Jaroslav Bachorik wrote:
>>>>> 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-