Allow duplicate variations of each OnlineAccountData in the import queue, but don't allow two entries that match exactly.

src/main/java/org/qortal/controller/OnlineAccountsManager.java

@@ -66,7 +66,7 @@ public class OnlineAccountsManager {
     private final ScheduledExecutorService executor = Executors.newScheduledThreadPool(4, new NamedThreadFactory("OnlineAccounts"));
     private volatile boolean isStopping = false;
 
-    private final Set<OnlineAccountData> onlineAccountsImportQueue = ConcurrentHashMap.newKeySet();
+    private final List<OnlineAccountData> onlineAccountsImportQueue = Collections.synchronizedList(new ArrayList<>());
 
     /**
      * Cache of 'current' online accounts, keyed by timestamp
@@ -184,9 +184,12 @@ public class OnlineAccountsManager {
 
         LOGGER.debug("Processing online accounts import queue (size: {})", this.onlineAccountsImportQueue.size());
 
+        // Take a copy of onlineAccountsImportQueue so we can safely remove whilst iterating
+        List<OnlineAccountData> onlineAccountsImportQueueCopy = new ArrayList<>(this.onlineAccountsImportQueue);
+
         Set<OnlineAccountData> onlineAccountsToAdd = new HashSet<>();
         try (final Repository repository = RepositoryManager.getRepository()) {
-            for (OnlineAccountData onlineAccountData : this.onlineAccountsImportQueue) {
+            for (OnlineAccountData onlineAccountData : onlineAccountsImportQueueCopy) {
                 if (isStopping)
                     return;
 
@@ -207,6 +210,19 @@ public class OnlineAccountsManager {
         }
     }
 
+    private boolean importQueueContainsExactMatch(OnlineAccountData acc) {
+        // Check if an item exists where all properties match exactly
+        // This is needed because signature and nonce are not compared in OnlineAccountData.equals()
+        synchronized (onlineAccountsImportQueue) {
+            return onlineAccountsImportQueue.stream().anyMatch(otherAcc ->
+                    acc.getTimestamp() == otherAcc.getTimestamp() &&
+                            Arrays.equals(acc.getPublicKey(), otherAcc.getPublicKey()) &&
+                            acc.getNonce() == otherAcc.getNonce() &&
+                            Arrays.equals(acc.getSignature(), otherAcc.getSignature())
+            );
+        }
+    }
+
     /**
      * Check if supplied onlineAccountData is superior (i.e. has a nonce value) than existing record.
      * Two entries are considered equal even if the nonce differs, to prevent multiple variations
@@ -809,6 +825,10 @@ public class OnlineAccountsManager {
                 // We have already validated this online account
                 continue;
 
+            if (this.importQueueContainsExactMatch(onlineAccountData))
+                // Identical online account data already present in queue
+                continue;
+
             boolean isNewEntry = onlineAccountsImportQueue.add(onlineAccountData);
 
             if (isNewEntry)