Fix #5862.

src/main/java/org/jabref/gui/groups/GroupNodeViewModel.java

@@ -90,7 +90,7 @@ public GroupNodeViewModel(BibDatabaseContext databaseContext, StateManager state
         // The wrapper created by the FXCollections will set a weak listener on the wrapped list. This weak listener gets garbage collected. Hence, we need to maintain a reference to this list.
         entriesList = databaseContext.getDatabase().getEntries();
         entriesList.addListener(this::onDatabaseChanged);
-        throttler = new DelayTaskThrottler(1000);
+        throttler = taskExecutor.createThrottler(1000);
 
         ObservableList<Boolean> selectedEntriesMatchStatus = EasyBind.map(stateManager.getSelectedEntries(), groupNode::matches);
         anySelectedEntriesMatched = BindingsHelper.any(selectedEntriesMatchStatus, matched -> matched);

src/main/java/org/jabref/gui/util/CurrentThreadTaskExecutor.java

@@ -1,5 +1,6 @@
 package org.jabref.gui.util;
 
+import java.util.WeakHashMap;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
@@ -8,6 +9,8 @@
 
 import javafx.concurrent.Task;
 
+import org.jabref.logic.util.DelayTaskThrottler;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -19,6 +22,7 @@
 public class CurrentThreadTaskExecutor implements TaskExecutor {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(CurrentThreadTaskExecutor.class);
+    private final WeakHashMap<DelayTaskThrottler, Void> throttlers = new WeakHashMap<>();
 
     /**
      * Executes the task on the current thread. The code is essentially taken from {@link
@@ -60,7 +64,14 @@ public <V> Future<?> schedule(BackgroundTask<V> task, long delay, TimeUnit unit)
 
     @Override
     public void shutdown() {
-        // Nothing to do here
+        throttlers.forEach((throttler, aVoid) -> throttler.shutdown());
+    }
+
+    @Override
+    public DelayTaskThrottler createThrottler(int delay) {
+        DelayTaskThrottler throttler = new DelayTaskThrottler(delay);
+        throttlers.put(throttler, null);
+        return throttler;
     }
 
     private class FailedFuture<T> implements Future<T> {

src/main/java/org/jabref/gui/util/DefaultTaskExecutor.java

@@ -1,6 +1,7 @@
 package org.jabref.gui.util;
 
 import java.util.Objects;
+import java.util.WeakHashMap;
 import java.util.concurrent.Callable;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
@@ -15,6 +16,8 @@
 import javafx.application.Platform;
 import javafx.concurrent.Task;
 
+import org.jabref.logic.util.DelayTaskThrottler;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -28,6 +31,7 @@ public class DefaultTaskExecutor implements TaskExecutor {
 
     private final ExecutorService executor = Executors.newFixedThreadPool(5);
     private final ScheduledExecutorService scheduledExecutor = Executors.newScheduledThreadPool(2);
+    private final WeakHashMap<DelayTaskThrottler, Void> throttlers = new WeakHashMap<>();
 
     /**
      *
@@ -110,6 +114,14 @@ public <V> Future<?> schedule(BackgroundTask<V> task, long delay, TimeUnit unit)
     public void shutdown() {
         executor.shutdownNow();
         scheduledExecutor.shutdownNow();
+        throttlers.forEach((throttler, aVoid) -> throttler.shutdown());
+    }
+
+    @Override
+    public DelayTaskThrottler createThrottler(int delay) {
+        DelayTaskThrottler throttler = new DelayTaskThrottler(delay);
+        throttlers.put(throttler, null);
+        return throttler;
     }
 
     private <V> Task<V> getJavaFXTask(BackgroundTask<V> task) {

src/main/java/org/jabref/gui/util/TaskExecutor.java

@@ -5,6 +5,8 @@
 
 import javafx.concurrent.Task;
 
+import org.jabref.logic.util.DelayTaskThrottler;
+
 /**
  * An object that executes submitted {@link Task}s. This
  * interface provides a way of decoupling task submission from the
@@ -46,4 +48,9 @@ public interface TaskExecutor {
      * Shutdown the task executor.
      */
     void shutdown();
+
+    /**
+     * Creates a new task throttler, and registers it so that it gets properly shutdown.
+     */
+    DelayTaskThrottler createThrottler(int delay);
 }