RFR: 8366082: Improve queue size computation in CPU-time sampler

[Francesco Andreuzzi]

On Mon, 25 Aug 2025 12:41:11 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

> Improve the sample queue size computation for the CPU-time sampler by increasing the size dynamically when needed, but keeping the default size small.

src/hotspot/share/jfr/periodic/sampling/jfrCPUTimeThreadSampler.cpp line 186:

> 184:     if (factor > 1) {
> 185:       u4 new_capacity = _capacity * factor > CPU_TIME_QUEUE_MAX_CAPACITY ? CPU_TIME_QUEUE_MAX_CAPACITY : capacity * factor;
> 186:       set_capacity(new_capacity);

Is it a problem if another thread changes `_capacity` since when you read it at L171, and the update is overwritten?

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PR Review Comment: https://git.openjdk.org/jdk/pull/26926#discussion_r2298149533