1 files changed, 43 insertions, 0 deletions

diff --git a/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/internal/engine/ListenerContainer.java b/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/internal/engine/ListenerContainer.java
new file mode 100644
index 00000000..34133bed
--- /dev/null
+++ b/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/internal/engine/ListenerContainer.java
@@ -0,0 +1,43 @@
+/*******************************************************************************
+ * Copyright (c) 2010-2013, Abel Hegedus, Istvan Rath and Daniel Varro
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-v20.html.
+ * 
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package tools.refinery.viatra.runtime.internal.engine;
+
+import static tools.refinery.viatra.runtime.matchers.util.Preconditions.checkArgument;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public abstract class ListenerContainer<Listener> {
+    
+    protected final Set<Listener> listeners;
+    
+    public ListenerContainer() {
+        this.listeners = new HashSet<Listener>();
+    }
+    
+    public synchronized void addListener(Listener listener) {
+        checkArgument(listener != null, "Cannot add null listener!");
+        boolean added = listeners.add(listener);
+        if(added) {
+            listenerAdded(listener);
+        }
+    }
+    
+    public synchronized void removeListener(Listener listener) {
+        checkArgument(listener != null, "Cannot remove null listener!");
+        boolean removed = listeners.remove(listener);
+        if(removed) {
+            listenerRemoved(listener);
+        }
+    }
+    
+    protected abstract void listenerAdded(Listener listener);
+    
+    protected abstract void listenerRemoved(Listener listener);
+}
\ No newline at end of file