Add mechanism to abort further processing of a score

osu.Server.Queues.ScoreStatisticsProcessor/Processors/ManiaKeyModeUserStatsProcessor.cs

@@ -21,7 +21,7 @@ namespace osu.Server.Queues.ScoreStatisticsProcessor.Processors
     [UsedImplicitly]
     public class ManiaKeyModeUserStatsProcessor : IProcessor
     {
-        public int Order => int.MaxValue;
+        public int Order => int.MaxValue - 1;
 
         public bool RunOnFailedScores => false;
         public bool RunOnLegacyScores => true;

osu.Server.Queues.ScoreStatisticsProcessor/Processors/MedalProcessor.cs

@@ -48,7 +48,7 @@ static MedalProcessor()
         public bool RunOnLegacyScores => true; // This is handled by each awarder.
 
         // This processor needs to run after the play count and hit statistics have been applied, at very least.
-        public int Order => int.MaxValue;
+        public int Order => int.MaxValue - 1;
 
         public void RevertFromUserStats(SoloScore score, UserStats userStats, int previousVersion, MySqlConnection conn, MySqlTransaction transaction, List<Action> postTransactionActions)
         {

osu.Server.Queues.ScoreStatisticsProcessor/Processors/ProcessingAbortedException.cs

@@ -0,0 +1,19 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+
+namespace osu.Server.Queues.ScoreStatisticsProcessor.Processors
+{
+    /// <summary>
+    /// Thrown by <see cref="IProcessor"/>s when the score's processing should be aborted immediately.
+    /// All side effects from the score processing should either be rolled back or not allowed to happen.
+    /// </summary>
+    public class ProcessingAbortedException : Exception
+    {
+        public ProcessingAbortedException(string message)
+            : base(message)
+        {
+        }
+    }
+}

osu.Server.Queues.ScoreStatisticsProcessor/ScoreStatisticsQueueProcessor.cs

@@ -235,7 +235,19 @@ private void processScore(ScoreItem item, bool force = false)
                         foreach (IProcessor p in enumerateValidProcessors(score))
                         {
                             stopwatch.Restart();
-                            p.ApplyToUserStats(score, userStats, conn, transaction, postTransactionActions);
+
+                            try
+                            {
+                                p.ApplyToUserStats(score, userStats, conn, transaction, postTransactionActions);
+                            }
+                            catch (ProcessingAbortedException abortException)
+                            {
+                                Console.WriteLine($"Aborting processing of score {item.Score.id}: {abortException.Message}");
+                                tags.Add("type:aborted");
+                                transaction.Rollback();
+                                return;
+                            }
+
                             DogStatsd.Timer("apply_time_elapsed", stopwatch.ElapsedMilliseconds, tags: item.Tags.Append($"processor:{p.GetType().ReadableName()}").ToArray());
                         }