Add shenandoah-jdk28: generational vs SATB Shenandoah, G1 and ZGC on a Spring Boot service (JEP 535 status probe included)

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01HmvoHH3ZnCEaPNXRpDxDZe

shenandoah-jdk28/scripts/gc_pauses.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+"""Stop-the-world pauses from a -Xlog:gc*:...:time,uptime log, restricted to an epoch-ms window.
+
+usage: gc_pauses.py LOG WINDOW_START_MS WINDOW_END_MS
+
+A pause is a log line that contains "Pause" and ends in "<n>ms" (G1 "Pause Young ... 4.2ms", ZGC
+"Y: Pause Mark Start 0.018ms", Shenandoah "Pause Init Mark 0.052ms"). The line without a duration that
+G1 and Shenandoah print when a pause *starts* is ignored, so nothing is counted twice.
+"""
+import re
+import sys
+from datetime import datetime
+
+LINE = re.compile(r"^\[(\d{4}-\d\d-\d\dT[\d:.]+[+-]\d{4})\].*?\bGC\(\d+\) .*Pause .* ([0-9.]+)ms$")
+
+log, lo, hi = sys.argv[1], int(sys.argv[2]), int(sys.argv[3])
+pauses = []
+for line in open(log, errors="replace"):
+    m = LINE.match(line.rstrip("\n"))
+    if not m:
+        continue
+    ts = datetime.strptime(m.group(1), "%Y-%m-%dT%H:%M:%S.%f%z").timestamp() * 1000
+    if lo <= ts <= hi:
+        pauses.append(float(m.group(2)))
+pauses.sort()
+n = len(pauses)
+
+
+def q(p):
+    return pauses[min(n - 1, int(p * n))] if n else 0.0
+
+
+print(f"pauses={n} pause_p50_ms={q(0.50):.3f} pause_p99_ms={q(0.99):.3f} pause_max_ms={pauses[-1] if n else 0.0:.3f} pause_total_ms={sum(pauses):.1f}")