I'm in favor of not adding complexity to ObjectName.equals(). The goal of this CR is to remove a bottleneck created by the use of String.intern() in ObjectName's constructors. This CR doesn't aim to optimize the ObjectName.equals() method.
An application can define an optimized method to compare two ObjectNames based on its knowledge of the patterns used by its ObjectNames. However, there's no simple way to workaround the bottleneck created by the String.intern() call. The Ops-Center team has experimented the removal of String.intern() by providing their own implementation of ObjectName and playing with the bootclasspath, but this is not a solution easy to deploy in a production environment. Fred On 2/23/12 8:44 PM, Eamonn McManus wrote:
I am not sure it is worth the complexity of extra checks. Do you have data showing that ObjectName.equals usually returns false? In a successful HashMap lookup, for example, it will usually return true since the equals method is used to guard against collisions, and collisions are rare by design. Meanwhile, String.equals is intrinsic in HotSpot so we may assume that it is highly optimized, and you are giving up that optimization if you use other comparisons. Éamonn On 23 February 2012 10:52, Olivier Lagneau <olivier.lagn...@oracle.com <mailto:olivier.lagn...@oracle.com>> wrote: Hi Frederic, Performance and typo comments. Regarding performance of ObjectName.equals method, which is certainely a frequent call on ObjectNames, I think that using inner fields (Property array for canonical name and domain length) would be more efficient than using String.equals() on these potentially very long strings. Two differents objectNames may often have the same length with different key/properties values, and may often be different only on the last property of the canonical name. The Property array field ca_array (comparing length and property contents) and domain length are good candidates to filter out more efficiently different objectNames, knowing that String.equals will compare every single char of the two char arrays. So for performance purpose, I suggest to filter out different objectNames by doing inner comparisons in the following order : length of the two canonical names, then domain_length, then ca_array size, then its content, and lastly if all of this fails to filter out, then use String.equals. _canonicalName = (new String(canonical_chars, 0, prop_index)); Typo : useless parentheses. Thanks, Olivier. -- Olivier Lagneau, olivier.lagn...@oracle.com <mailto:olivier.lagn...@oracle.com> Oracle, Grenoble Engineering Center - France Phone : +33 4 76 18 80 09 <tel:%2B33%204%2076%2018%2080%2009> Fax : +33 4 76 18 80 23 <tel:%2B33%204%2076%2018%2080%2023> Frederic Parain said on date 2/23/2012 6:01 PM: No particular reason. But after thinking more about it, equals() should be a better choice, clearer code, and the length check in equals() implementation is likely to help performance of ObjectName's comparisons as ObjectNames are often long with a common section at the beginning. I've updated the webrev: http://cr.openjdk.java.net/~__fparain/6988220/webrev.01/ <http://cr.openjdk.java.net/~fparain/6988220/webrev.01/> Thanks, Fred On 2/23/12 4:58 PM, Vitaly Davidovich wrote: Hi Frederic, Just curious - why are you checking string equality via compareTo() instead of equals()? Thanks Sent from my phone On Feb 23, 2012 10:37 AM, "Frederic Parain" <frederic.par...@oracle.com <mailto:frederic.par...@oracle.com> <mailto:frederic.parain@__oracle.com <mailto:frederic.par...@oracle.com>>> wrote: This a simple fix to solve CR 6988220: http://bugs.sun.com/____bugdatabase/view_bug.do?bug_____id=6988220 <http://bugs.sun.com/__bugdatabase/view_bug.do?bug___id=6988220> <http://bugs.sun.com/__bugdatabase/view_bug.do?bug___id=6988220 <http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6988220>> The use of String.intern() in the ObjectName class prevents the class the scale well when more than 20K ObjectNames are managed. The fix simply removes the use of String.intern(), and uses regular String instead. The Object.equals() method is modified too to make a regular String comparison. The complexity of this method now depends on the length of the ObjectName's canonical name, and is not impacted any more by the number of ObjectName instances being handled. The Webrev: http://cr.openjdk.java.net/~____fparain/6988220/webrev.00/ <http://cr.openjdk.java.net/~__fparain/6988220/webrev.00/> <http://cr.openjdk.java.net/~__fparain/6988220/webrev.00/ <http://cr.openjdk.java.net/~fparain/6988220/webrev.00/>> I've tested this fix with the jdk_lang and jdk_management test suites. Thanks, Fred -- Frederic Parain - Oracle Grenoble Engineering Center - France Phone: +33 4 76 18 81 17 <tel:%2B33%204%2076%2018%2081%2017> <tel:%2B33%204%2076%2018%2081%__2017> Email: frederic.par...@oracle.com <mailto:frederic.par...@oracle.com> <mailto:Frederic.Parain@__oracle.com <mailto:frederic.par...@oracle.com>>
-- Frederic Parain - Oracle Grenoble Engineering Center - France Phone: +33 4 76 18 81 17 Email: frederic.par...@oracle.com
