Avoid leaks in Long GC disruption tests

We can leak disrupted threads here since we never wait for them to
complete after freeing them from their loops. This commit addresses this
by joining on disrupted threads, and addresses fallout from trying to
join here.

Relates #24338

test/framework/src/main/java/org/elasticsearch/test/disruption/LongGCDisruption.java

@@ -106,6 +106,15 @@ public class LongGCDisruption extends SingleNodeDisruption {
                     logger.warn("failed to stop node [{}]'s threads within [{}] millis. Stopping thread stack trace:\n {}"
                         , disruptedNode, getStoppingTimeoutInMillis(), stackTrace(stoppingThread.getStackTrace()));
                     stoppingThread.interrupt(); // best effort;
+                    try {
+                        /*
+                         * We need to join on the stopping thread in case it has stopped a thread that is in a critical section and needs to
+                         * be resumed.
+                         */
+                        stoppingThread.join();
+                    } catch (InterruptedException e) {
+                        throw new RuntimeException(e);
+                    }
                     throw new RuntimeException("stopping node threads took too long");
                 }
                 // block detection checks if other threads are blocked waiting on an object that is held by one
@@ -228,23 +237,39 @@ public class LongGCDisruption extends SingleNodeDisruption {
                 if (thread.isAlive() && nodeThreads.add(thread)) {
                     liveThreadsFound = true;
                     logger.trace("stopping thread [{}]", threadName);
-                    thread.suspend();
-                    // double check the thread is not in a shared resource like logging. If so, let it go and come back..
-                    boolean safe = true;
-                    safe:
-                    for (StackTraceElement stackElement : thread.getStackTrace()) {
-                        String className = stackElement.getClassName();
-                        for (Pattern unsafePattern : getUnsafeClasses()) {
-                            if (unsafePattern.matcher(className).find()) {
-                                safe = false;
-                                break safe;
+                    // we assume it is not safe to suspend the thread
+                    boolean safe = false;
+                    try {
+                        /*
+                         * At the bottom of this try-block we will know whether or not it is safe to suspend this thread; we start by
+                         * assuming that it is safe.
+                         */
+                        boolean definitelySafe = true;
+                        thread.suspend();
+                        // double check the thread is not in a shared resource like logging; if so, let it go and come back
+                        safe:
+                        for (StackTraceElement stackElement : thread.getStackTrace()) {
+                            String className = stackElement.getClassName();
+                            for (Pattern unsafePattern : getUnsafeClasses()) {
+                                if (unsafePattern.matcher(className).find()) {
+                                    // it is definitely not safe to suspend the thread
+                                    definitelySafe = false;
+                                    break safe;
+                                }
                             }
                         }
-                    }
-                    if (!safe) {
-                        logger.trace("resuming thread [{}] as it is in a critical section", threadName);
-                        thread.resume();
-                        nodeThreads.remove(thread);
+                        safe = definitelySafe;
+                    } finally {
+                        if (!safe) {
+                            /*
+                             * Do not log before resuming as we might be interrupted while logging in which case we will throw an
+                             * interrupted exception and never resume the stopped thread that is in a critical section. Also, logging before
+                             * resuming makes for confusing log messages if we never hit the resume.
+                             */
+                            thread.resume();
+                            logger.trace("resumed thread [{}] as it is in a critical section", threadName);
+                            nodeThreads.remove(thread);
+                        }
                     }
                 }
             }

test/framework/src/test/java/org/elasticsearch/test/disruption/LongGCDisruptionTests.java

@@ -22,6 +22,8 @@ import org.elasticsearch.common.Nullable;
 import org.elasticsearch.test.ESTestCase;
 
 import java.lang.management.ThreadInfo;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -69,8 +71,8 @@ public class LongGCDisruptionTests extends ESTestCase {
         final CountDownLatch pauseUnderLock = new CountDownLatch(1);
         final LockedExecutor lockedExecutor = new LockedExecutor();
         final AtomicLong ops = new AtomicLong();
+        final Thread[] threads = new Thread[10];
         try {
-            Thread[] threads = new Thread[10];
             for (int i = 0; i < 10; i++) {
                 // at least one locked and one none lock thread
                 final boolean lockedExec = (i < 9 && randomBoolean()) || i == 0;
@@ -101,6 +103,9 @@ public class LongGCDisruptionTests extends ESTestCase {
         } finally {
             stop.set(true);
             pauseUnderLock.countDown();
+            for (final Thread thread : threads) {
+                thread.join();
+            }
         }
     }
 
@@ -121,8 +126,8 @@ public class LongGCDisruptionTests extends ESTestCase {
         final AtomicBoolean stop = new AtomicBoolean();
         final LockedExecutor lockedExecutor = new LockedExecutor();
         final AtomicLong ops = new AtomicLong();
+        final Thread[] threads = new Thread[10];
         try {
-            Thread[] threads = new Thread[10];
             for (int i = 0; i < 10; i++) {
                 threads[i] = new Thread(() -> {
                     for (int iter = 0; stop.get() == false; iter++) {
@@ -150,6 +155,9 @@ public class LongGCDisruptionTests extends ESTestCase {
             assertBusy(() -> assertThat(ops.get(), greaterThan(first)));
         } finally {
             stop.set(true);
+            for (final Thread thread : threads) {
+                thread.join();
+            }
         }
     }
 
@@ -183,6 +191,7 @@ public class LongGCDisruptionTests extends ESTestCase {
         final CountDownLatch pauseUnderLock = new CountDownLatch(1);
         final LockedExecutor lockedExecutor = new LockedExecutor();
         final AtomicLong ops = new AtomicLong();
+        final List<Thread> threads = new ArrayList<>();
         try {
             for (int i = 0; i < 5; i++) {
                 // at least one locked and one none lock thread
@@ -206,6 +215,7 @@ public class LongGCDisruptionTests extends ESTestCase {
                 });
 
                 thread.setName("[" + disruptedNodeName + "][" + i + "]");
+                threads.add(thread);
                 thread.start();
             }
 
@@ -224,12 +234,13 @@ public class LongGCDisruptionTests extends ESTestCase {
                     }
                 });
                 thread.setName("[" + blockedNodeName + "][" + i + "]");
+                threads.add(thread);
                 thread.start();
             }
             // make sure some threads of test_node are under lock
             underLock.await();
             disruption.startDisrupting();
-            waitForBlockDetectionResult.await(30, TimeUnit.SECONDS);
+            assertTrue(waitForBlockDetectionResult.await(30, TimeUnit.SECONDS));
             disruption.stopDisrupting();
 
             ThreadInfo threadInfo = blockDetectionResult.get();
@@ -240,6 +251,9 @@ public class LongGCDisruptionTests extends ESTestCase {
         } finally {
             stop.set(true);
             pauseUnderLock.countDown();
+            for (final Thread thread : threads) {
+                thread.join();
+            }
         }
     }
 }