RFR 8041565: JMX ObjectName could be refactored to save memory
Daniel Fuchs
daniel.fuchs at oracle.com
Thu Aug 13 09:53:53 UTC 2015
Hi Jaroslav,
On 12/08/15 18:05, Jaroslav Bachorik wrote:
> On 5.8.2015 08:04, Eamonn McManus wrote:
>> That makes me sad. The limit is clearly a detail of this particular
>> implementation and should not be enshrined in the spec.
>> Éamonn
>
> I re-requested CCC for not mentioning the exact limit in the docs and it
> has been approved (thanks to Joe for quick turnaround).
>
> The update webrev: http://cr.openjdk.java.net/~jbachorik/8041565/webrev.04
Why are index and in_index now declared as short? Is that a left over
from the original webrev?
445 short index = 0;
501 short in_index;
should these be reverted to 'int' ?
Otherwise - this looks good...
-- daniel
>
> -JB-
>
>>
>>
>> 2015-08-05 8:02 GMT-07:00 Jaroslav Bachorik
>> <jaroslav.bachorik at oracle.com>:
>>> On 5.8.2015 16:53, Eamonn McManus wrote:
>>>>
>>>> I would remove the spec changes about the limit on the domain length,
>>>> which are a property of this particular implementation. It's perfectly
>>>> reasonable to blow up if the domain length is > 536,870,911, but
>>>> there's no reason for it to be in the spec.
>>>
>>>
>>> Well, CCC board had a different opinion. That's why this limit is
>>> documented
>>> in the spec.
>>>
>>> -JB-
>>>
>>>
>>>> Éamonn
>>>>
>>>>
>>>> 2015-08-05 4:48 GMT-07:00 Jaroslav Bachorik
>>>> <jaroslav.bachorik at oracle.com>:
>>>>>
>>>>> 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-
>>>>>
>>>>>
>>>>>
>>>
>
More information about the serviceability-dev
mailing list