RFR: Samples/jmh sample 39 memory access

[Aleksey Shipilev]

On Wed, 12 Oct 2022 23:34:59 GMT, Michael Mirwaldt <duke at openjdk.org> wrote:

> I propose this sample because overlooking the memory layout of e.g. ArrayLists can be a pitfall for benchmarks.
> This new sample makes users of JMH aware of this problem. It teaches them how to use JMH right.
> What do you think?

Quick review...

jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_39_MemoryAccess.java line 64:

> 62:      *
> 63:      * Benchmark                               Mode  Cnt        Score      Error  Units
> 64:      * JMHSample_39_MemoryAccess.sumArray      avgt   25        5.117 ±    0.039  ns/op

5 ns to sum 1M elements seems way too low.

jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_39_MemoryAccess.java line 87:

> 85:         long sum = 0;
> 86:         for (int i = 0; i < N; i++) {
> 87:             sum = intArray[i];

This needs to be `+=`.

jmh-samples/src/main/java/org/openjdk/jmh/samples/JMHSample_39_MemoryAccess.java line 96:

> 94:         long sum = 0;
> 95:         for (int i = 0; i < N; i++) {
> 96:             sum = intList.get(i);

This needs to be `+=`.

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PR: https://git.openjdk.org/jmh/pull/85