JMH Thread index? (original) (raw)

Aleksey Shipilev aleksey.shipilev at oracle.com
Mon May 6 12:39:34 PDT 2013

On 05/06/2013 10:10 PM, Nitsan Wakart wrote:

What I meant was programmatically... in my benchmark code I have an array which is the benchmark state with an element per thread, I'd like to know the number of threads so I can allocate for the number of threads.

You can't possibly do this at this point. There's no feedback to the benchmark how many threads are running, although it should be fixed with future @Param works.

Similarly, each thread needs to access it's own element, so I'd like to have a thread index which correlates to the thread stats reported in the output.

The best way to showcase this would be having the asymmetric benchmark. I remember doing the false-sharing benchmark like this:

@State(Scope.Group) @OutputTimeUnit(TimeUnit.NANOSECONDS) public class MyFalseSharingBench {

volatile int x1;
volatile int x2;
volatile int  x3,  x4,  x5,  x6,  x7,  x8,  x9, x10;
volatile int x11, x12, x13, x14, x15, x16, x17, x18, x19;
volatile int x20;

@GenerateMicroBenchmark(BenchmarkType.AverageTimePerOp)
@Group("sharing")
public void thread1() {
   x1++;
}

@GenerateMicroBenchmark(BenchmarkType.AverageTimePerOp)
@Group("sharing")
public void thread2() {
   x2++;
}

@GenerateMicroBenchmark(BenchmarkType.AverageTimePerOp)
@Group("sharing")
public void thread3() {
   x20++;
}

}

$ ... Iteration 2 (5s in 3 threads): thread1{t=1} = 28.039, thread2{t=1} = 32.116, thread3{t=1} = 11.998 nsec/op

It gets really beautiful with @Contended.

-Aleksey.

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