It's important to note that our experiments show that the byte codes are
different.
Gary
On Mon, Sep 29, 2014 at 10:29 AM, Paul Benedict <pbened...@apache.org>
wrote:
> Open JDKers, I am forwarding an email to get some clarification. It's been
> a common understanding that foreach should perform no differently than the
> equivalent for-loop . However, some fellow developers claim there is a
> noticable difference in their microbenchmarking. Can you help explain what
> is really going on? It's either the case there is a true difference (a
> result that would surprise me) or the results are within a margin of error
> that make the results insignificant. Please advise.
>
> Cheers,
> Paul
>
> ---------- Forwarded message ----------
> From: Remko Popma <remko.po...@gmail.com>
> Date: Fri, Sep 26, 2014 at 8:43 AM
> Subject: Re: No for each loop comment?
> To: Log4J Developers List <log4j-...@logging.apache.org>
>
>
> On Windows it looks like normal for loops are slightly faster than
> for-each loops, especially for small arrays of primitives. This could be
> noise, since we are talking about 5 nanoseconds where the baseline (an
> empty method invocation) is 12 nanos.
>
> On Solaris 10 and Red Hat Enterprise Linux the baseline is so large (255
> nanos and 1910 nanos respectively) that any difference we are seeing is
> just noise.
>
> All benchmarks were run with one fork, one thread, 10 warmup iterations
> and 10 test iterations.
>
> *Windows 7 (64bit) with Java 1.8.0_05, 2-core Intel i5-3317u CPU @1.70Ghz
> with hyperthreading switched on (4 virtual cores)*
> Benchmark Mode Samples
> Score Score error Units
> o.a.l.l.p.j.LoopsBenchmark.baseline sample 154947
> 12.432 0.550 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10000ForEachLoop sample 126597
> 2759.592 3.431 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10000ForLoop sample 126494
> 2761.729 3.127 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray1000ForEachLoop sample 154124
> 292.880 1.065 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray1000ForLoop sample 156155
> 288.751 1.101 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray100ForEachLoop sample 191980
> 41.826 0.870 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray100ForLoop sample 193770
> 36.894 0.782 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10ForEachLoop sample 190847
> 22.393 0.618 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10ForLoop sample 192552
> 17.146 0.560 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10000ForEachLoop sample 173839
> 31959.057 14.341 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10000ForLoop sample 171137
> 32461.985 14.353 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray1000ForEachLoop sample 97495
> 3591.200 4.852 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray1000ForLoop sample 101560
> 3445.998 4.010 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray100ForEachLoop sample 102796
> 438.207 1.923 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray100ForLoop sample 102333
> 439.576 2.139 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10ForEachLoop sample 113924
> 58.957 1.247 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10ForLoop sample 120416
> 60.712 1.284 ns/op
>
>
> // For loops for Object arrays are similar but return the total XOR of the
> element hashcodes.
>
> private int forEachLoop(final int[] array) {
> int result = 0;
> for (final int element : array) {
> result ^= element;
> }
> return result;
> }
>
> private int forLoop(final int[] array) {
> int result = 0;
> for (int i = 0; i < array.length; i++) {
> result ^= array[i];
> }
> return result;
> }
>
>
>
> *Solaris 10 (64bit) with JDK1.7.0_06-b24 (Oracle Hotspot), 2 quad-core
> Xeon X5570 dual CPUs @2.93Ghz with hyperthreading switched on (16 virtual
> cores)*
> Benchmark Mode Samples
> Score Score error Units
> o.a.l.l.p.j.LoopsBenchmark.baseline sample 110212
> 255.300 0.201 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10000ForEachLoop sample 187808
> 3938.055 1.207 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10000ForLoop sample 187897
> 3937.929 0.748 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray1000ForEachLoop sample 123989
> 606.631 0.626 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray1000ForLoop sample 123973
> 609.565 0.416 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray100ForEachLoop sample 126933
> 294.204 0.280 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray100ForLoop sample 127070
> 296.411 0.223 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10ForEachLoop sample 113400
> 261.519 0.181 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10ForLoop sample 111637
> 260.435 0.115 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10000ForEachLoop sample 115872
> 48154.673 18.846 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10000ForLoop sample 116777
> 47793.868 17.615 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray1000ForEachLoop sample 138432
> 5256.767 2.451 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray1000ForLoop sample 136644
> 5325.377 2.388 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray100ForEachLoop sample 166653
> 773.541 0.330 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray100ForLoop sample 166570
> 774.513 0.574 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10ForEachLoop sample 178754
> 317.232 0.134 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10ForLoop sample 180165
> 316.189 0.238 ns/op
>
> *64 bit RHEL 6.5 (Linux 2.6.32-431.el6.x86_64) with JDK1.7.0_05-b06
> (Oracle Hotspot), 4 quad-core Xeon X5570 CPUs @2.93GHz with hyperthreading
> switched on (16 virtual cores)*
> Benchmark Mode Samples
> Score Score error Units
> o.a.l.l.p.j.LoopsBenchmark.baseline sample 114783
> 1910.576 29.256 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10000ForEachLoop sample 194584
> 5132.885 25.137 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10000ForLoop sample 196672
> 4811.572 52.072 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray1000ForEachLoop sample 133119
> 1967.213 28.970 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray1000ForLoop sample 133804
> 2004.501 31.554 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray100ForEachLoop sample 142439
> 1575.329 6.457 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray100ForLoop sample 142215
> 1957.714 27.815 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10ForEachLoop sample 130826
> 1980.301 30.818 ns/op
> o.a.l.l.p.j.LoopsBenchmark.intArray10ForLoop sample 132654
> 1589.120 8.449 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10000ForEachLoop sample 126947
> 43301.320 50.589 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10000ForLoop sample 126117
> 43574.129 55.272 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray1000ForEachLoop sample 143697
> 5831.250 19.667 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray1000ForLoop sample 163244
> 4823.096 13.180 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray100ForEachLoop sample 162502
> 1930.819 24.136 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray100ForLoop sample 171619
> 1625.806 10.385 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10ForEachLoop sample 172226
> 1888.683 22.554 ns/op
> o.a.l.l.p.j.LoopsBenchmark.objArray10ForLoop sample 188838
> 1581.979 6.322 ns/op
>
>
>
>
> On Fri, Sep 26, 2014 at 2:56 AM, Matt Sicker <boa...@gmail.com> wrote:
>
>> The foreach over an array looks like it's supposed to compile to the same
>> thing:
>>
>> https://jcp.org/aboutJava/communityprocess/jsr/tiger/enhanced-for.html
>>
>> Same goes for .length which is supposed to be a final field which would
>> allow for inlining by the JIT I'd imagine (hence why we use final
>> everywhere):
>>
>> http://docs.oracle.com/javase/specs/jls/se7/html/jls-10.html#jls-10.7
>>
>>
>>>>> On 24 September 2014 22:12, Gary Gregory <garydgreg...@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Why does this "//noinspection ForLoopReplaceableByForEach" comment
>>>>>> mean?
>>>>>>
>>>>>> Why not for an enhanced for each loop?
>>>>>>
>>>>>> private static boolean contains(final Marker parent, final Marker...
>>>>>> localParents) {
>>>>>> //noinspection ForLoopReplaceableByForEach
>>>>>> for (int i = 0, localParentsLength = localParents.length;
>>>>>> i < localParentsLength; i++) {
>>>>>> final Marker marker = localParents[i];
>>>>>> if (marker == parent) {
>>>>>> return true;
>>>>>> }
>>>>>> }
>>>>>> return false;
>>>>>> }
>>>>>>
>>>>>> Thanks,
>>>>>> Gary
>>>>>>
>>>>>>
>>>>>>
--
E-Mail: garydgreg...@gmail.com | ggreg...@apache.org
Java Persistence with Hibernate, Second Edition
<http://www.manning.com/bauer3/>
JUnit in Action, Second Edition <http://www.manning.com/tahchiev/>
Spring Batch in Action <http://www.manning.com/templier/>
Blog: http://garygregory.wordpress.com
Home: http://garygregory.com/
Tweet! http://twitter.com/GaryGregory
