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/*
* Copyright (c) 2026 AtLarge Research
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
package org.opendc.experiments
import jdk.jfr.consumer.RecordingFile
import java.nio.file.Path
import kotlin.math.sqrt
/**
* Heap usage statistics derived from a single JFR recording.
*
* All memory values are in megabytes and are computed from the `heapUsed` field
* of `jdk.GCHeapSummary` events captured during one JMH iteration.
*
* @property avgMb Mean heap usage across all GC samples in the recording (MB).
* @property maxMb Peak heap usage observed in any single GC sample (MB).
* @property stdMb Population standard deviation of heap usage across all samples (MB).
* @property sampleCount Number of `jdk.GCHeapSummary` events found in the recording.
*/
data class HeapStats(
val avgMb: Double,
val maxMb: Double,
val stdMb: Double,
val sampleCount: Int,
)
/**
* Parses a JFR recording file and computes heap usage statistics from its
* `jdk.GCHeapSummary` events.
*
* Each `jdk.GCHeapSummary` event is emitted by the JVM after a GC cycle and
* carries the `heapUsed` value (bytes). This function collects all such values,
* then computes mean, peak, and standard deviation, converting the results from
* bytes to megabytes.
*
* @param jfrPath Path to the `.jfr` recording file to analyze.
* @return A [HeapStats] instance if at least one `jdk.GCHeapSummary` event was
* found, or `null` if the recording contained no such events (e.g., no GC
* occurred during the iteration).
*/
fun analyzeHeap(jfrPath: Path): HeapStats? {
val samples = mutableListOf<Long>()
RecordingFile(jfrPath).use { recording ->
while (recording.hasMoreEvents()) {
val event = recording.readEvent()
if (event.eventType.name == "jdk.GCHeapSummary") {
samples.add(event.getLong("heapUsed"))
}
}
}
if (samples.isEmpty()) return null
val avg = samples.average()
val max = samples.max().toDouble()
val std = sqrt(samples.sumOf { (it - avg).let { d -> d * d } } / samples.size)
val toMb = 1.0 / (1024.0 * 1024.0)
return HeapStats(avg * toMb, max * toMb, std * toMb, samples.size)
}
/**
* Standalone entry point for inspecting the heap statistics of an existing JFR file.
*
* Reads `build/bench.jfr` (the default output path used by [OpenDCBenchmark]) and
* prints a human-readable summary to stdout. Useful for quickly inspecting the
* recording from the most recently completed benchmark iteration without re-running
* the full benchmark.
*
* Exits with an error if the file contains no `jdk.GCHeapSummary` events.
*/
fun main() {
val path = Path.of("build/bench.jfr")
val stats = analyzeHeap(path) ?: error("No jdk.GCHeapSummary events found in $path")
println("Heap statistics from $path (${stats.sampleCount} GC samples):")
println(" Avg: ${"%.2f".format(stats.avgMb)} MB")
println(" Max: ${"%.2f".format(stats.maxMb)} MB")
println(" Std: ${"%.2f".format(stats.stdMb)} MB")
}
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