Use ArrayList for update send queue instead of a LinkedList

Unless we need to remove elements in the middle of a list, an array based variant is always faster.

src/refit/replica/execution/REFITExecutor.java

@@ -53,7 +53,7 @@ public class REFITExecutor {
 		this.enableCheckpoints = false;
 		this.createLightWeightCheckpoints = false;
 		this.enableUpdates = false;
-		this.updateSendQueue = new LinkedList<>();
+		this.updateSendQueue = new ArrayList<>();
 		this.nodeProgresses = new long[REFITConfig.ADDRESSES.length];
 		Arrays.fill(nodeProgresses, -1L);
 		this.replyHashes = new byte[REFITConfig.ADDRESSES.length][];
@@ -343,7 +343,7 @@ public class REFITExecutor {
 	// ###########
 
 	private boolean enableUpdates;
-	private final Queue<REFITUpdate> updateSendQueue;
+	private final List<REFITUpdate> updateSendQueue;
 
 
 	public void setEnableUpdates(boolean enableUpdates) {
@@ -409,12 +409,12 @@ public class REFITExecutor {
 		REFITUpdateMessage update;
 		if (updateSendQueue.size() > 1) {
 			// Assign batch update the UID and agreement sequence number of the first individual update
-			REFITUpdate firstUpdate = updateSendQueue.peek();
+			REFITUpdate firstUpdate = updateSendQueue.get(0);
 			update = new REFITBatchUpdate(firstUpdate.agreementSeqNr(), replicaID, updateSendQueue);
-			updateSendQueue.clear();
 		} else {
-			update = updateSendQueue.poll();
+			update = updateSendQueue.get(0);
 		}
+		updateSendQueue.clear();
 		updateSender.broadcast(update);
 	}