Synchronize peer data lookups.

Without this we could broadcast the same data multiple times, due to more than one thread processing the same message from different peers.

src/main/java/org/qortal/controller/arbitrary/ArbitraryDataManager.java

@@ -36,6 +36,7 @@ public class ArbitraryDataManager extends Thread {
 	private static final long ARBITRARY_REQUEST_TIMEOUT = 5 * 1000L; // ms
 
 	private static ArbitraryDataManager instance;
+	private final Object peerDataLock = new Object();
 
 	private boolean buildInProgress = false;
 
@@ -679,39 +680,42 @@ public class ArbitraryDataManager extends Thread {
 
 		boolean containsNewEntry = false;
 
-		try (final Repository repository = RepositoryManager.getRepository()) {
-			for (byte[] signature : signatures) {
-
-				// Check if a record already exists for this hash/peer combination
-				ArbitraryPeerData existingEntry = repository.getArbitraryRepository()
-						.getArbitraryPeerDataForSignatureAndPeer(signature, peer.getPeerData().getAddress().toString());
-
-				if (existingEntry == null) {
-					// We haven't got a record of this mapping yet, so add it
-					LOGGER.info("Adding arbitrary peer: {} for signature {}", peerAddress, Base58.encode(signature));
-					ArbitraryPeerData arbitraryPeerData = new ArbitraryPeerData(signature, peer);
-					repository.getArbitraryRepository().save(arbitraryPeerData);
-					repository.saveChanges();
+		// Synchronize peer data lookups to make this process thread safe. Otherwise we could broadcast
+		// the same data multiple times, due to more than one thread processing the same message from different peers
+		synchronized (this.peerDataLock) {
+			try (final Repository repository = RepositoryManager.getRepository()) {
+				for (byte[] signature : signatures) {
+
+					// Check if a record already exists for this hash/peer combination
+					ArbitraryPeerData existingEntry = repository.getArbitraryRepository()
+							.getArbitraryPeerDataForSignatureAndPeer(signature, peer.getPeerData().getAddress().toString());
+
+					if (existingEntry == null) {
+						// We haven't got a record of this mapping yet, so add it
+						LOGGER.info("Adding arbitrary peer: {} for signature {}", peerAddress, Base58.encode(signature));
+						ArbitraryPeerData arbitraryPeerData = new ArbitraryPeerData(signature, peer);
+						repository.getArbitraryRepository().save(arbitraryPeerData);
+						repository.saveChanges();
+
+						// Remember that this data is new, so that it can be re-broadcast later
+						containsNewEntry = true;
+					}
+				}
 
-					// Remember that this data is new, so that it can be re-broadcast later
-					containsNewEntry = true;
+				// If at least one signature in this batch was new to us, we should re-broadcast the message to the
+				// network in case some peers haven't received it yet
+				if (containsNewEntry) {
+					LOGGER.info("Rebroadcasting arbitrary signature list for peer {}", peerAddress);
+					Network.getInstance().broadcast(broadcastPeer -> arbitrarySignaturesMessage);
+				} else {
+					// Don't re-broadcast as otherwise we could get into a loop
 				}
-			}
 
-			// If at least one signature in this batch was new to us, we should re-broadcast the message to the
-			// network in case some peers haven't received it yet
-			if (containsNewEntry) {
-				LOGGER.info("Rebroadcasting arbitrary signature list for peer {}", peerAddress);
-				Network.getInstance().broadcast(broadcastPeer -> arbitrarySignaturesMessage);
-			}
-			else {
-				// Don't re-broadcast as otherwise we could get into a loop
+				// If anything needed saving, it would already have called saveChanges() above
+				repository.discardChanges();
+			} catch (DataException e) {
+				LOGGER.error(String.format("Repository issue while processing arbitrary transaction signature list from peer %s", peer), e);
 			}
-
-			// If anything needed saving, it would already have called saveChanges() above
-			repository.discardChanges();
-		} catch (DataException e) {
-			LOGGER.error(String.format("Repository issue while processing arbitrary transaction signature list from peer %s", peer), e);
 		}
 	}