Fix ConcurrentModificationException in RemoteRecorder

common/src/main/java/ctbrec/recorder/RemoteRecorder.java

@@ -15,6 +15,7 @@ import java.util.List;
 import java.util.Optional;
 import java.util.Set;
 import java.util.UUID;
+import java.util.concurrent.locks.ReentrantLock;
 
 import org.json.JSONObject;
 import org.slf4j.Logger;
@@ -70,6 +71,7 @@ public class RemoteRecorder implements Recorder {
     private List<Model> models = Collections.emptyList();
     private List<Model> onlineModels = Collections.emptyList();
     private List<Recording> recordings = Collections.emptyList();
+    private ReentrantLock modelGroupLock = new ReentrantLock();
     private Set<ModelGroup> modelGroups = new HashSet<>();
     private List<Site> sites;
     private long spaceTotal = -1;
@@ -202,8 +204,13 @@ public class RemoteRecorder implements Recorder {
             throw new IOException("Server returned error " + resp.status + " " + resp.msg);
         }
 
-        modelGroups.clear();
-        modelGroups.addAll(resp.groups);
+        modelGroupLock.lock();
+        try {
+            modelGroups.clear();
+            modelGroups.addAll(resp.groups);
+        } finally {
+            modelGroupLock.unlock();
+        }
     }
 
     private void addHmacIfNeeded(String msg, Builder builder) throws InvalidKeyException, NoSuchAlgorithmException, UnsupportedEncodingException {
@@ -691,7 +698,12 @@ public class RemoteRecorder implements Recorder {
 
     @Override
     public Set<ModelGroup> getModelGroups() {
-        return new HashSet<>(modelGroups);
+        modelGroupLock.lock();
+        try {
+            return new HashSet<>(modelGroups);
+        } finally {
+            modelGroupLock.unlock();
+        }
     }
 
     @Override