Rework of processIncomingTransactionsQueue() so that it no longer holds the lock while processing.

This should fix an issue where network threads could be blocked when new transactions arrived, due to waiting for the incomingTransactions lock to free up.

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

@@ -830,6 +830,10 @@ public class Controller extends Thread {
 		}
 	}
 
+	private void removeIncomingTransaction(byte[] signature) {
+		incomingTransactions.removeIf(t -> Arrays.equals(t.getSignature(), signature));
+	}
+
 	private void processIncomingTransactionsQueue() {
 		if (this.incomingTransactions.size() == 0) {
 			// Don't bother locking if there are no new transactions to process
@@ -853,17 +857,20 @@ public class Controller extends Thread {
 		}
 
 		try (final Repository repository = RepositoryManager.getRepository()) {
+			LOGGER.debug("Processing incoming transactions queue (size {})...", this.incomingTransactions.size());
+
+			// Take a copy of incomingTransactions so we can release the lock
+			List<TransactionData>incomingTransactionsCopy = new ArrayList<>(this.incomingTransactions);
 
 			// Iterate through incoming transactions list
-			synchronized (this.incomingTransactions) { // Required in order to safely iterate a synchronizedList()
-				Iterator iterator = this.incomingTransactions.iterator();
+			Iterator iterator = incomingTransactionsCopy.iterator();
 			while (iterator.hasNext()) {
 				if (isStopping) {
 					return;
 				}
 
 				if (Synchronizer.getInstance().isSyncRequestPending()) {
-						LOGGER.debug("Breaking out of transaction processing loop with {} remaining, because a sync request is pending", this.incomingTransactions.size());
+					LOGGER.debug("Breaking out of transaction processing loop with {} remaining, because a sync request is pending", incomingTransactionsCopy.size());
 					return;
 				}
 
@@ -873,7 +880,7 @@ public class Controller extends Thread {
 				// Check signature
 				if (!transaction.isSignatureValid()) {
 					LOGGER.trace(() -> String.format("Ignoring %s transaction %s with invalid signature", transactionData.getType().name(), Base58.encode(transactionData.getSignature())));
-						iterator.remove();
+					removeIncomingTransaction(transactionData.getSignature());
 					continue;
 				}
 
@@ -881,13 +888,13 @@ public class Controller extends Thread {
 
 				if (validationResult == ValidationResult.TRANSACTION_ALREADY_EXISTS) {
 					LOGGER.trace(() -> String.format("Ignoring existing transaction %s", Base58.encode(transactionData.getSignature())));
-						iterator.remove();
+					removeIncomingTransaction(transactionData.getSignature());
 					continue;
 				}
 
 				if (validationResult == ValidationResult.NO_BLOCKCHAIN_LOCK) {
 					LOGGER.trace(() -> String.format("Couldn't lock blockchain to import unconfirmed transaction", Base58.encode(transactionData.getSignature())));
-						iterator.remove();
+					removeIncomingTransaction(transactionData.getSignature());
 					continue;
 				}
 
@@ -906,17 +913,17 @@ public class Controller extends Thread {
 						// Invalid, unconfirmed transaction has become stale - add to invalidUnconfirmedTransactions so that we don't keep requesting it
 						invalidUnconfirmedTransactions.put(signature58, expiry);
 					}
-						iterator.remove();
+					removeIncomingTransaction(transactionData.getSignature());
 					continue;
 				}
 
 				LOGGER.debug(() -> String.format("Imported %s transaction %s", transactionData.getType().name(), Base58.encode(transactionData.getSignature())));
-					iterator.remove();
-				}
+				removeIncomingTransaction(transactionData.getSignature());
 			}
 		} catch (DataException e) {
 			LOGGER.error(String.format("Repository issue while processing incoming transactions", e));
 		} finally {
+			LOGGER.debug("Finished processing incoming transactions queue");
 			blockchainLock.unlock();
 		}
 	}