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/IHM_benchmark_results_i7-2600K.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
