Java 27 and 26: runnable demos and captured output for every JEP, plus version lanes

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01B38FGKKam5SCGgwgduVAh3

scripts/g1-cost.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# What does the switch cost on a machine that used to get Serial?  1 CPU, 2 GB, three runs each.
+# Timing is indicative only: one shared machine, one process per run. Read the SHAPE, not the digits.
+#   ./scripts/g1-cost.sh              -> docs/output/04-g1-cost-1cpu.txt        (4000 batches, ~6-8 s per run)
+#   BATCHES=400 OUTNAME=05-g1-cost-1cpu-short.txt ./scripts/g1-cost.sh   (a short-lived process, e.g. a CI job)
+set -euo pipefail
+source "$(dirname "$0")/env.sh"
+BUILD="$ROOT/build/g1"; mkdir -p "$BUILD"
+"$JDK27/bin/javac" --release 26 -d "$BUILD" "$ROOT"/g1-container/src/*.java
+RUNS="${RUNS:-3}"; BATCHES="${BATCHES:-4000}"; OUTNAME="${OUTNAME:-04-g1-cost-1cpu.txt}"
+{
+  echo "# Allocation workload, 1 CPU / 2 GB container, $BATCHES batches x 50,000 objects, $RUNS runs per configuration (indicative, not a benchmark)"
+  echo "# 'default' means nobody passed a collector flag."
+  echo
+  for cfg in "$IMG26|" "$IMG27|" "$IMG27|-XX:+UseSerialGC"; do
+    img="${cfg%%|*}"; flag="${cfg##*|}"
+    for i in $(seq 1 "$RUNS"); do
+      echo "=== $img ${flag:-default} run $i"
+      docker run --rm --cpus=1 --memory=2g -v "$BUILD:/app:ro" "$img" \
+        java $flag -cp /app Workload "$BATCHES" | grep -v -E '^allocated'
+    done
+    echo
+  done
+} > "$OUT/$OUTNAME" 2>&1
+cat "$OUT/$OUTNAME"