Break out of incoming transactions processing loop if we need to sync.

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

@@ -856,6 +856,11 @@ public class Controller extends Thread {
 						return;
 					}
 
+					if (Synchronizer.getInstance().isSyncRequestPending()) {
+						LOGGER.debug("Breaking out of transaction processing loop with {} remaining, because a sync request is pending", this.incomingTransactions.size());
+						return;
+					}
+
 					TransactionData transactionData = (TransactionData) iterator.next();
 					Transaction transaction = Transaction.fromData(repository, transactionData);
 

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

@@ -82,6 +82,7 @@ public class Synchronizer extends Thread {
 	private volatile int syncPercent = 0;
 
 	private static volatile boolean requestSync = false;
+	private boolean syncRequestPending = false;
 
 	// Keep track of invalid blocks so that we don't keep trying to sync them
 	private Map<String, Long> invalidBlockSignatures = Collections.synchronizedMap(new HashMap<>());
@@ -123,6 +124,8 @@ public class Synchronizer extends Thread {
 						// Something went wrong, so try again next time
 						requestSync = true;
 					}
+					// Remember that we have a pending sync request if this attempt failed
+					syncRequestPending = !success;
 				}
 			}
 		} catch (InterruptedException e) {
@@ -143,6 +146,10 @@ public class Synchronizer extends Thread {
 		return this.isSynchronizing;
 	}
 
+	public boolean isSyncRequestPending() {
+		return this.syncRequestPending;
+	}
+
 	public Integer getSyncPercent() {
 		synchronized (this.syncLock) {
 			return this.isSynchronizing ? this.syncPercent : null;