IdentityHashMap.[keySet|values|entrySet].toArray speed-up (original) (raw)

Peter Levart peter.levart at gmail.com
Thu Feb 14 13:24:28 UTC 2013

Hello Mike,

On 02/13/2013 09:21 PM, Mike Duigou wrote:

This looks like excellent contribution Peter!

I will proceed with the testing needed to integrate your improved toArray()/toArray(T[]) implementations. I have created an issue, JDK-8008167, for this patch. I am surprised that this didn't get more attention back in December as it does seem to offer significant benefits for size and performance.

It would if IdentityHashMap was used instead of HashMap for annotations caching. But that's something that should be done on the global basis (there are various places where Maps of annotations are constructed: reflection classes, AnnotationParser, ...).

There's also opportunity to use IdentityHashMap instead of LinkedHashMap (totally unnecessary, since it is never iterated !!??) for holding member values of annotation instances (the Map is keyed by String objects, but they could be interned at map creation time - the same string values are interned already, since they are equal to names of methods of the annotation interfaces and retrieval is already using the interned Strings: Method.getName() - see AnnotationInvocationHandler)...

Let me know if testing finds anything or if there's anything I can do (regarding coding style, etc).

Regards, Peter

Thanks, Mike On Dec 12 2012, at 01:07 , Peter Levart wrote:

Hi all,

I propose a patch to java.util.IdentityHashMap to speed-up toArray methods of it's keySet, values and entrySet views: http://dl.dropbox.com/u/101777488/jdk8-tl/IdentityHashMap/webrev.01/index.html I toyed with the possibility to replace HashMap-s, that are used in java.lang.Class and java.lang.reflect.[Field|Method|Constructor] to hold cached annotations, with IdentityHashMap-s. They are a perfect replacement, since keys in these maps are java.lang.Class objects. They are more compact then HashMap-s. This is the comparison of allocated heap bytes between HashMap and IdentityHashMap for various sizes and corresponding capacities which takes into account the size of the Map object, the size of allocated array and the size of Map.Entry-s in case of HM (IHM doesn't have them) and the size of associated values Collection view (allocated when dumping annotations to array). HM-s for annotations are currently allocated with default initial capacity (16). I propose to allocate IHM-s with initial capacity 8 that fits to hold 5 entries which is enough for typical annotation use cases on one hand and still makes improvement for any case on the other: 32 bit JVM: | HashMap | IdentityHashMap | size|capacity bytes|capacity bytes|IHM.bytes-HM.bytes --------+-----------------+-----------------+------------------ 0| 16 144| 8 136| -8 1| 16 168| 8 136| -32 2| 16 192| 8 136| -56 3| 16 216| 8 136| -80 4| 16 240| 8 136| -104 5| 16 264| 8 136| -128 6| 16 288| 16 200| -88 7| 16 312| 16 200| -112 8| 16 336| 16 200| -136 9| 16 360| 16 200| -160 10| 16 384| 16 200| -184 11| 16 408| 16 200| -208 12| 16 432| 32 328| -104 13| 32 520| 32 328| -192 14| 32 544| 32 328| -216 15| 32 568| 32 328| -240 16| 32 592| 32 328| -264 17| 32 616| 32 328| -288 18| 32 640| 32 328| -312 19| 32 664| 32 328| -336 20| 32 688| 32 328| -360 40| 64 1296| 64 584| -712 60| 128 2032| 128 1096| -936 80| 128 2512| 128 1096| -1416 100| 256 3504| 256 2120| -1384 120| 256 3984| 256 2120| -1864 140| 256 4464| 256 2120| -2344 160| 256 4944| 256 2120| -2824 180| 256 5424| 512 4168| -1256 64 bit JVM: | HashMap | IdentityHashMap | size|capacity bytes|capacity bytes|IHM.bytes-HM.bytes --------+-----------------+-----------------+------------------ 0| 16 248| 8 240| -8 1| 16 296| 8 240| -56 2| 16 344| 8 240| -104 3| 16 392| 8 240| -152 4| 16 440| 8 240| -200 5| 16 488| 8 240| -248 6| 16 536| 16 368| -168 7| 16 584| 16 368| -216 8| 16 632| 16 368| -264 9| 16 680| 16 368| -312 10| 16 728| 16 368| -360 11| 16 776| 16 368| -408 12| 16 824| 32 624| -200 13| 32 1000| 32 624| -376 14| 32 1048| 32 624| -424 15| 32 1096| 32 624| -472 16| 32 1144| 32 624| -520 17| 32 1192| 32 624| -568 18| 32 1240| 32 624| -616 19| 32 1288| 32 624| -664 20| 32 1336| 32 624| -712 40| 64 2552| 64 1136| -1416 60| 128 4024| 128 2160| -1864 80| 128 4984| 128 2160| -2824 100| 256 6968| 256 4208| -2760 120| 256 7928| 256 4208| -3720 140| 256 8888| 256 4208| -4680 160| 256 9848| 256 4208| -5640 180| 256 10808| 512 8304| -2504 I hope I've got that tables right. This is the program to compute them: https://raw.github.com/plevart/jdk8-tl/JEP-149.2/test/src/test/IHMvsHMsizes.java IHM is also more performant when retrieving the values by keys. The only area in which it lags behind HashMap and is important for accessing annotations in bulk is the toArray method of the values view. In particular for small sizes. The above patch speeds-up those methods by using index iteration instead of Iterator. Here are some speed-up comparisons: https://raw.github.com/plevart/jdk8-tl/JEP-149.2/test/IHMbenchmarkresultsi7-2600K.txt They are obtained by running the following micro benchmark: https://raw.github.com/plevart/jdk8-tl/JEP-149.2/test/src/test/IdentityHashMapTest.java Even if IHM doesn't replace HM for holding annotations, a speed-up improvement is an improvement.

Regards, Peter

More information about the core-libs-dev mailing list