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

[Aleksey Shipilev]

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.
>