8323792: ThreadSnapshot::initialize can cause assert in Thread::check_for_dangling_thread_pointer (possibility of dangling Thread pointer)

src/hotspot/share/services/management.cpp

@@ -1095,7 +1095,8 @@ static void do_thread_dump(ThreadDumpResult* dump_result,
 //               maxDepth == 0  requests no stack trace.
 //   infoArray - array of ThreadInfo objects
 //
-// QQQ - Why does this method return a value instead of void?
+// This method returns jint for historical reasons.
+// The value has no meaning, it is always 0.  The one caller never uses it, this method could equally be void.
 JVM_ENTRY(jint, jmm_GetThreadInfo(JNIEnv *env, jlongArray ids, jint maxDepth, jobjectArray infoArray))
   // Check if threads is null
   if (ids == nullptr || infoArray == nullptr) {
@@ -1141,7 +1142,7 @@ JVM_ENTRY(jint, jmm_GetThreadInfo(JNIEnv *env, jlongArray ids, jint maxDepth, jo
     for (int i = 0; i < num_threads; i++) {
       jlong tid = ids_ah->long_at(i);
       JavaThread* jt = dump_result.t_list()->find_JavaThread_from_java_tid(tid);
-      if (jt == nullptr) {
+      if (jt == nullptr || !Thread::is_JavaThread_protected_by_TLH(jt)) {
         // if the thread does not exist or now it is terminated,
         // create dummy snapshot
         dump_result.add_thread_snapshot();

test/jdk/java/lang/management/ThreadMXBean/ThreadInfoStress.java

@@ -0,0 +1,142 @@
+/*
+ * Copyright (c) 2025, 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
+ * @bug 8323792
+ * @summary Stress ThreadMXBean.getThreadInfo with Threads terminating
+ * @requires test.thread.factory != "Virtual"
+ * @run main/othervm ThreadInfoStress
+ */
+
+import java.lang.management.*;
+import java.util.*;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class ThreadInfoStress {
+
+    // The assert in Thread::check_for_dangling_thread_pointer happens very quickly.
+    // Run for some seconds as a short stress test:
+    private static final int DURATION_MS = 5 * 1000;
+    private static final int NUM_THREADS = 10;
+
+    private static com.sun.management.ThreadMXBean mbean = (com.sun.management.ThreadMXBean) ManagementFactory.getThreadMXBean();
+
+    static long [] ids = new long[NUM_THREADS];
+    static ThreadInfo [] infos = new ThreadInfo[NUM_THREADS];
+    static volatile int count = 0;
+
+    public static void main(String[] argv)
+        throws Exception {
+
+        int totalCount = 0;
+
+        startThreads(NUM_THREADS, ids);
+        new MyGetThreadInfoThread(ids).start();
+
+        long t1 = System.currentTimeMillis();
+        long t2 = t1 + DURATION_MS;
+
+        do {
+            // Threads are running and will finish at different times.
+            count = countThreadInfo(infos);
+            totalCount += count;
+            System.out.println("ThreadInfos found (Threads alive): " + count);
+            if (count == 0) {
+                startThreads(NUM_THREADS, ids);
+            }
+            goSleep(100);
+        } while (System.currentTimeMillis() < t2);
+
+        if (totalCount == 0) {
+            // If mitigations for the assert are extremely cautious, and no ThreadInfo are gathered, fail:
+            throw new RuntimeException("Failed: No ThreadInfos found.");
+        }
+        System.out.println("Done.");
+    }
+
+    // Start threads, store ids in shared array.
+    private static void startThreads(int count, long [] ids) {
+        System.out.println("Starting " + count + " Threads...");
+        for (int i = 0; i < count; i++) {
+            Thread thread = new MyThread(i);
+            thread.start();
+            ids[i] = thread.threadId();
+        }
+    }
+
+    // Scan array for non-null ThreadInfo, return count.
+    private static int countThreadInfo(ThreadInfo [] infos) {
+        int count = 0;
+        System.out.print("ThreadInfos found:");
+        for (ThreadInfo ti: infos) {
+            if (ti != null) {
+                System.out.print(" ");
+                System.out.print(ti.getThreadId());
+                count++;
+            }
+        }
+        System.out.println();
+        return count;
+    }
+
+    private static void goSleep(long ms) {
+        try {
+            Thread.sleep(ms);
+        } catch (InterruptedException e) {
+            System.out.println("goSleep: " + e);
+        }
+    }
+
+    // Thread that sleeps, then ends.
+    static class MyThread extends Thread {
+        long lifeMs;
+
+        public MyThread(long lifeMs) {
+            super("MyThread-" + lifeMs);
+            this.lifeMs = lifeMs * lifeMs * 10;
+        }
+
+        public void run() {
+            goSleep(lifeMs);
+        }
+    }
+
+    // Continually call getThreadInfo on a shared array of Thread ids,
+    // storing in the shared array of ThreadInfo.
+    // The ids will get stale, using ids of new or ending or ended threads is part of the test.
+    static class MyGetThreadInfoThread extends Thread {
+        long [] ids;
+
+        public MyGetThreadInfoThread(long [] ids) {
+            this.ids = ids;
+        }
+
+        public void run() {
+            while (true) {
+                infos = mbean.getThreadInfo(ids, 0 /* maxDepth */);
+                goSleep(10);
+            }
+        }
+    }
+}