RFR (S): CR 8005926: (thread) Merge ThreadLocalRandom state into java.lang.Thread

[Chris Hegarty]

For what it is worth, it is on my list for today.

-Chris.

On 14/01/2013 13:31, Aleksey Shipilev wrote:
> I understand everyone is busy with JDK8 milestone, but maybe some
> critical people have missed this note? It would be terrific if someone
> could review this (or even sponsor it!).
>
> Thanks,
> Aleksey.
>
> On 01/11/2013 02:31 AM, Aleksey Shipilev wrote:
>> Hi,
>>
>> Submitting this on behalf of Doug Lea. The webrev is here:
>>    http://cr.openjdk.java.net/~shade/8005926/webrev.00/
>>
>> Bottom-line: merge ThreadLocalRandom state into Thread, to optimize many
>> use cases around j.u.c.* code. The simple performance tests on 2x2 i5,
>> Linux x86_64, 4 threads, 5 forks, 3x3s warmup, 5x3s measurement:
>>
>> JDK8 (baseline)
>>                TLR.nextInt():  6.4 +- 0.1 ns/op
>>      TLR.current().nextInt(): 16.1 +- 0.4 ns/op
>>           TL.get().nextInt(): 19.1 +- 0.6 ns/op
>>
>> JDK8 (patched)
>>                TLR.nextInt():  6.5 +- 0.2 ns/op
>>      TLR.current().nextInt():  6.4 +- 0.1 ns/op
>>           TL.get().nextInt(): 17.2 +- 2.0 ns/op
>>
>> First line shows the peak performance of TLR itself, everything over
>> that is the ThreadLocal overhead. One can see the patched version
>> bypasses ThreadLocal machinery completely, and the overhead is slim to none.
>>
>> N.B. It gets especially interesting when there are many ThreadLocals
>> registered. Making 1M ThreadLocals and pre-touching them bloats the
>> thread-local maps, and we get:
>>
>> JDK8 (baseline), contaminators = 1M:
>>                TLR.nextInt():  6.4 +- 0.1 ns/op
>>      TLR.current().nextInt(): 21.7 +- 5.3 ns/op
>>           TL.get().nextInt(): 28.7 +- 1.1 ns/op
>>
>> JDK8 (patched), contaminators = 1M:
>>                TLR.nextInt():  6.6 +- 0.2 ns/op
>>      TLR.current().nextInt():  6.5 +- 0.1 ns/op
>>           TL.get().nextInt(): 29.4 +- 0.5 ns/op
>>
>> Note that patched version successfully dodges this pathological case.
>>
>> Testing:
>>    - Doug tested on his platforms
>>    - Tested Linux x86_64 to build and run successfully
>>    - JPRT builds are OK
>>    - JPRT tests are OK (modulo some weird lambda/default-methods test
>> failures in jdk8/tl)
>>
>> Attribution:
>>    - dl: original patch
>>    - shade: testing, copyright headers, etc.
>>
>> -Aleksey.
>>
>