8345294: test/jdk/java/lang/Thread/virtual/RetryMonitorEnterWhenPinned.java timeout with JTREG_TEST_THREAD_FACTORY=Virtual

Reviewed-by: alanb

Author: Doug Lea

src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java

@@ -610,12 +610,11 @@ public class ForkJoinPool extends AbstractExecutorService {
      * it tries to deactivate()), giving up (and rescanning) on "ctl"
      * contention. To avoid missed signals during deactivation, the
      * method rescans and reactivates if there may have been a missed
-     * (external) signal during deactivation. To reduce false-alarm
-     * reactivations while doing so, we scan multiple times
-     * (analogously to method quiescent()) before trying to
-     * reactivate.  Because idle workers are often not yet blocked
-     * (parked), we use a WorkQueue field to advertise that a waiter
-     * actually needs unparking upon signal.
+     * signal during deactivation. To reduce false-alarm reactivations
+     * while doing so, we scan multiple times (analogously to method
+     * quiescent()) before trying to reactivate.  Because idle workers
+     * are often not yet blocked (parked), we use a WorkQueue field to
+     * advertise that a waiter actually needs unparking upon signal.
      *
      * Quiescence. Workers scan looking for work, giving up when they
      * don't find any, without being sure that none are available.
@@ -1996,7 +1995,7 @@ private int deactivate(WorkQueue w, int phase) {
             return IDLE;
         int p = phase | IDLE, activePhase = phase + (IDLE << 1);
         long pc = ctl, qc = (activePhase & LMASK) | ((pc - RC_UNIT) & UMASK);
-        w.stackPred = (int)pc;                // set ctl stack link
+        int sp = w.stackPred = (int)pc;       // set ctl stack link
         w.phase = p;
         if (!compareAndSetCtl(pc, qc))        // try to enqueue
             return w.phase = phase;           // back out on possible signal
@@ -2006,18 +2005,18 @@ private int deactivate(WorkQueue w, int phase) {
             (qs = queues) == null || (n = qs.length) <= 0)
             return IDLE;                      // terminating
         int prechecks = Math.min(ac, 2);      // reactivation threshold
-        for (int k = Math.max(n + (n << 1), SPIN_WAITS << 1);;) {
-            WorkQueue q; int cap; ForkJoinTask<?>[] a;
+        for (int k = Math.max(n << 2, SPIN_WAITS << 1);;) {
+            WorkQueue q; int cap; ForkJoinTask<?>[] a; long c;
             if (w.phase == activePhase)
                 return activePhase;
             if (--k < 0)
                 return awaitWork(w, p);       // block, drop, or exit
-            if ((k & 1) != 0)
-                Thread.onSpinWait();          // interleave spins and rechecks
-            else if ((q = qs[k & (n - 1)]) != null &&
-                     (a = q.array) != null && (cap = a.length) > 0 &&
+            if ((q = qs[k & (n - 1)]) == null)
+                Thread.onSpinWait();
+            else if ((a = q.array) != null && (cap = a.length) > 0 &&
                      a[q.base & (cap - 1)] != null && --prechecks < 0 &&
-                     ctl == qc && compareAndSetCtl(qc, pc))
+                     (int)(c = ctl) == activePhase &&
+                     compareAndSetCtl(c, (sp & LMASK) | ((c + RC_UNIT) & UMASK)))
                 return w.phase = activePhase; // reactivate
         }
     }

test/jdk/java/lang/Thread/virtual/Starvation.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/* @test
+ * @library /test/lib
+ * @bug 8345294
+ * @run main/othervm --enable-native-access=ALL-UNNAMED Starvation 100000
+ */
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicReference;
+import jdk.test.lib.thread.VThreadPinner;
+
+public class Starvation {
+    public static void main(String[] args) throws Exception {
+        int iterations = Integer.parseInt(args[0]);
+
+        for (int i = 0; i < iterations; i++) {
+            var exRef = new AtomicReference<Exception>();
+            Thread thread =  Thread.startVirtualThread(() -> {
+                try {
+                    runTest();
+                } catch (Exception e) {
+                    exRef.set(e);
+                }
+            });
+            while (!thread.join(Duration.ofSeconds(1))) {
+                System.out.format("%s iteration %d waiting for %s%n", Instant.now(), i, thread);
+            }
+            Exception ex = exRef.get();
+            if (ex != null) {
+                throw ex;
+            }
+        }
+    }
+
+    static void runTest() throws InterruptedException {
+        int nprocs = Runtime.getRuntime().availableProcessors();
+
+        var threads = new ArrayList<Thread>();
+        Object lock = new Object();
+        synchronized (lock) {
+            for (int i = 0; i < nprocs - 1; i++) {
+                var started = new CountDownLatch(1);
+                Thread thread = Thread.startVirtualThread(() -> {
+                    started.countDown();
+                    VThreadPinner.runPinned(() -> {
+                        synchronized (lock) {
+                        }
+                    });
+                });
+                started.await();
+                threads.add(thread);
+            }
+        }
+
+        for (Thread t : threads) {
+            t.join();
+        }
+    }
+}