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
2026-09-21 15:08:50 +00:00
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+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Virtual threads and synchronized: until JEP 491 (Java 24) a virtual thread that blocked inside a synchronized
+ * block kept its carrier thread (was "pinned"). With ONE carrier, four virtual threads that each sleep 200 ms inside
+ * synchronized on their own lock take about 800 ms if pinned (one at a time) and about 200 ms if not (all at once).
+ * Run by scripts/lanes.sh with -Djdk.virtualThreadScheduler.parallelism=1 -Djdk.virtualThreadScheduler.maxPoolSize=1
+ * Chapter: docs/14-lanes-21-to-25.md
+ */
+public class PinningDemo {
+    public static void main(String[] args) throws Exception {
+        System.out.println("java.version = " + System.getProperty("java.version"));
+        List<Thread> threads = new ArrayList<>();
+        long t0 = System.nanoTime();
+        for (int i = 0; i < 4; i++) {
+            Object lock = new Object();
+            threads.add(Thread.ofVirtual().start(() -> {
+                synchronized (lock) {
+                    try { Thread.sleep(200); } catch (InterruptedException ignored) { }
+                }
+            }));
+        }
+        for (Thread t : threads) t.join();
+        long ms = (System.nanoTime() - t0) / 1_000_000;
+        System.out.println("4 virtual threads, 1 carrier, sleep(200) inside synchronized: "
+                + (ms >= 700 ? "SERIALISED (pinned): about 4 x 200 ms" : "OVERLAPPED (not pinned): about 200 ms"));
+    }
+}