On May 30 2012, at 07:05 , Ulf Zibis wrote:
> Hi,
>
> there are still some "Yoda" style expressions in String, HashMap, maybe
> more...
They can be slightly surprising but aren't a bug. Nothing in the style
guidelines suggests that they shouldn't be used.
> there is still {@inheritDoc} in String.hash32(), which points to nowhere,
> since interface Hashable32 is not implemented.
Now corrected.
> -Ulf
>
> Am 30.05.2012 01:05, schrieb Mike Duigou:
>> Another round of updates for Java 7 [1] and Java 8 [2] implementations. This
>> revision incorporates Remi's suggestions and some feedback from Doug Lea
>> regarding applying the per-instance seed to the result of String.hash32()
>>
>> [1] althashing "7" webrev :
>> http://cr.openjdk.java.net/~mduigou/althashing7/10/webrev/
>> [2] althashing "8" webrev :
>> http://cr.openjdk.java.net/~mduigou/althashing8/10/webrev/
>>
>> Barring any emergencies this will be integrated to both Java 7 and Java 8 on
>> Wednesday May 30th, 2012.
>>
>> Thanks to all who provided feedback!
>>
>> Mike
>>
>>
>> On May 25 2012, at 10:38 , Rémi Forax wrote:
>>
>>> On 05/24/2012 09:34 PM, Mike Duigou wrote:
>>>> Hello All;
>>>>
>>>> I have updated the webrevs for alternative hashing for String with
>>>> feedback from Remi, Doug, Ulf and internal reviewers.
>>>>
>>>> Additional feedback is welcome.
>>>>
>>>> Mike
>>>>
>>>> [1] althashing "7" webrev :
>>>> http://cr.openjdk.java.net/~mduigou/althashing7/9/webrev/
>>>> [2] althashing "8" webrev :
>>>> http://cr.openjdk.java.net/~mduigou/althashing8/9/webrev/
>>> Hello Mike,
>>> just two small issues.
>>>
>>> In WeakHashMap.hash(), the null check should be done at callsite,
>> It's not even needed at the callsite as it always follows a maskNull call.
>>
>>> the call to hash32() should be directly returned like in HashMap.
>> Fixed.
>>
>>> Is Hashable32 is used anymore ?
>> It's the "source" of the hash32 method that String now implements and
>> hopefully more later. This bit is sort of unfinished in this patch but I
>> would like to leave it in for now.
>>
>> Mike
>>
>>
>>> Rémi
>>>
>>>> On May 22 2012, at 22:16 , Mike Duigou wrote:
>>>>
>>>>> Dear OpenJDK CoreLibs community,
>>>>>
>>>>> A significant enhancement to the Java SE hashing-based Map
>>>>> implementations in planned for inclusion in Java SE 7u6. All of the
>>>>> hashing based Map implementations: HashMap, Hashtable, LinkedHashMap,
>>>>> WeakHashMap and ConcurrentHashMap will now use an enhanced hashing
>>>>> algorithm for string keys when the capacity of the hash table has ever
>>>>> grown beyond 512 entries. The enhanced hashing implementation uses the
>>>>> murmur3 hashing algorithm[1] along with random hash seeds and index
>>>>> masks. These enhancements mitigate cases where colliding String hash
>>>>> values could result in a performance bottleneck.
>>>>>
>>>>> In order to provide the greatest opportunity for developers to test
>>>>> compatibility with their applications this change will be incorporated
>>>>> into JDK7u6 build 12 and JDK8 build 39. Both builds are planned for
>>>>> release next week. ***For 7u6 build 12 only, the alternative hashing will
>>>>> be unconditionally enabled (always on).*** The threshold default will be
>>>>> reset to the intended release default (512) for 7u6 build 13.
>>>>>
>>>>> The quick promotion of this change into builds with limited opportunity
>>>>> for public review and the special behaviour for build 12 is intended to
>>>>> make it easier for developers to test their application compatibility.
>>>>> Feedback on the approach, implementation, compatibility and performance
>>>>> is eagerly sought and encouraged both before *and after* this change is
>>>>> incorporated into the OpenJDK repositories.
>>>>>
>>>>> A new system property, jdk.map.althashing.threshold, allows adjustment of
>>>>> the threshold for enabling the enhanced hashing algorithm. If changed
>>>>> from the default value of 512, the enhanced hashing will be invoked any
>>>>> time after map capacity exceeds the value of
>>>>> jdk.map.althashing.threshold. To completely disable the enhanced hashing
>>>>> (not recommended), set jdk.map.althashing.threshold to -1 or a very large
>>>>> number such as 2^31 -1 (Integer.MAX_VALUE).
>>>>>
>>>>> The iteration order of keys, values and entries for hash-based maps where
>>>>> the new algorithm has been invoked will vary for each HashMap instance.
>>>>> While the Java SE Map documentation makes no promises that iteration
>>>>> order of items returned from Maps will be consistent, developers should
>>>>> check if their applications have incorrectly created a dependency on the
>>>>> iteration order of Map entries, keys or values.
>>>>>
>>>>> Webrevs for the Java 7u6 and 8 changes are available for download at [2]
>>>>> and [3] for your review. There are some important differences between the
>>>>> Java 7 and 8 implementations of this enhancement. Most specifically in
>>>>> the Java 8 implementation alternative string hashing is always
>>>>> enabled--no threshold is used for enablement and alternative hashing
>>>>> cannot be disabled. (The Java 8 implementation completely ignores the
>>>>> jdk.map.althashing.threshold system property). The Java 8 implementation
>>>>> is also subject to additional refinement as Java 8 develops.
>>>>>
>>>>> If you have any questions or concerns with this planned enhancement,
>>>>> please use the corelibs development mailing
>>>>> list,<mailto:core-libs-dev@openjdk.java.net>, or you may also respond
>>>>> privately to me if you prefer.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> Mike
>>>>>
>>>>> [1] Murmur3 : https://code.google.com/p/smhasher/wiki/MurmurHash3
>>>>> [2] althashing "7" webrev :
>>>>> http://cr.openjdk.java.net/~mduigou/althashing7/8/webrev/
>>>>> [3] althashing "8" webrev :
>>>>> http://cr.openjdk.java.net/~mduigou/althashing8/8/webrev/
>>
