Only write when writes occur

Also add finaliser logic for safety. Also better threading. Also more cleanup.

osu.Game/Beatmaps/BeatmapManager.cs

@@ -172,7 +172,7 @@ namespace osu.Game.Beatmaps
         /// <param name="archive">The beatmap to be imported.</param>
         public BeatmapSetInfo Import(ArchiveReader archive)
         {
-            using ( contextFactory.GetForWrite()) // used to share a context for full import. keep in mind this will block all writes.
+            using (contextFactory.GetForWrite()) // used to share a context for full import. keep in mind this will block all writes.
             {
                 // create a new set info (don't yet add to database)
                 var beatmapSet = createBeatmapSetInfo(archive);
@@ -181,7 +181,7 @@ namespace osu.Game.Beatmaps
                 var existingHashMatch = beatmaps.BeatmapSets.FirstOrDefault(b => b.Hash == beatmapSet.Hash);
                 if (existingHashMatch != null)
                 {
-                    undelete(existingHashMatch);
+                    Undelete(existingHashMatch);
                     return existingHashMatch;
                 }
 
@@ -315,9 +315,9 @@ namespace osu.Game.Beatmaps
         /// <param name="beatmapSet">The beatmap set to delete.</param>
         public void Delete(BeatmapSetInfo beatmapSet)
         {
-            using (var db = contextFactory.GetForWrite())
+            using (var usage = contextFactory.GetForWrite())
             {
-                var context = db.Context;
+                var context = usage.Context;
 
                 context.ChangeTracker.AutoDetectChangesEnabled = false;
 
@@ -378,11 +378,16 @@ namespace osu.Game.Beatmaps
             if (beatmapSet.Protected)
                 return;
 
-            using (var db = contextFactory.GetForWrite())
+            using (var usage = contextFactory.GetForWrite())
             {
-                db.Context.ChangeTracker.AutoDetectChangesEnabled = false;
+                usage.Context.ChangeTracker.AutoDetectChangesEnabled = false;
-                undelete(beatmapSet);
+
-                db.Context.ChangeTracker.AutoDetectChangesEnabled = true;
+                if (!beatmaps.Undelete(beatmapSet)) return;
+
+                if (!beatmapSet.Protected)
+                    files.Reference(beatmapSet.Files.Select(f => f.FileInfo).ToArray());
+
+                usage.Context.ChangeTracker.AutoDetectChangesEnabled = true;
             }
         }
 
@@ -398,21 +403,6 @@ namespace osu.Game.Beatmaps
         /// <param name="beatmap">The beatmap difficulty to restore.</param>
         public void Restore(BeatmapInfo beatmap) => beatmaps.Restore(beatmap);
 
-        /// <summary>
-        /// Returns a <see cref="BeatmapSetInfo"/> to a usable state if it has previously been deleted but not yet purged.
-        /// Is a no-op for already usable beatmaps.
-        /// </summary>
-        /// <param name="beatmaps">The store to restore beatmaps from.</param>
-        /// <param name="files">The store to restore beatmap files from.</param>
-        /// <param name="beatmapSet">The beatmap to restore.</param>
-        private void undelete(BeatmapSetInfo beatmapSet)
-        {
-            if (!beatmaps.Undelete(beatmapSet)) return;
-
-            if (!beatmapSet.Protected)
-                files.Reference(beatmapSet.Files.Select(f => f.FileInfo).ToArray());
-        }
-
         /// <summary>
         /// Retrieve a <see cref="WorkingBeatmap"/> instance for the provided <see cref="BeatmapInfo"/>
         /// </summary>

osu.Game/Beatmaps/BeatmapStore.cs

@@ -31,9 +31,9 @@ namespace osu.Game.Beatmaps
         /// <param name="beatmapSet">The beatmap to add.</param>
         public void Add(BeatmapSetInfo beatmapSet)
         {
-            using (var db = ContextFactory.GetForWrite())
+            using (var usage = ContextFactory.GetForWrite())
             {
-                var context = db.Context;
+                var context = usage.Context;
 
                 foreach (var beatmap in beatmapSet.Beatmaps.Where(b => b.Metadata != null))
                 {
@@ -48,6 +48,7 @@ namespace osu.Game.Beatmaps
                 }
 
                 context.BeatmapSetInfo.Attach(beatmapSet);
+
                 BeatmapSetAdded?.Invoke(beatmapSet);
             }
         }
@@ -73,11 +74,12 @@ namespace osu.Game.Beatmaps
         /// <returns>Whether the beatmap's <see cref="BeatmapSetInfo.DeletePending"/> was changed.</returns>
         public bool Delete(BeatmapSetInfo beatmapSet)
         {
-            using ( ContextFactory.GetForWrite())
+            using (ContextFactory.GetForWrite())
             {
                 Refresh(ref beatmapSet, BeatmapSets);
 
                 if (beatmapSet.DeletePending) return false;
+
                 beatmapSet.DeletePending = true;
             }
 
@@ -92,11 +94,12 @@ namespace osu.Game.Beatmaps
         /// <returns>Whether the beatmap's <see cref="BeatmapSetInfo.DeletePending"/> was changed.</returns>
         public bool Undelete(BeatmapSetInfo beatmapSet)
         {
-            using ( ContextFactory.GetForWrite())
+            using (ContextFactory.GetForWrite())
             {
                 Refresh(ref beatmapSet, BeatmapSets);
 
                 if (!beatmapSet.DeletePending) return false;
+
                 beatmapSet.DeletePending = false;
             }
 
@@ -116,6 +119,7 @@ namespace osu.Game.Beatmaps
                 Refresh(ref beatmap, Beatmaps);
 
                 if (beatmap.Hidden) return false;
+
                 beatmap.Hidden = true;
 
                 BeatmapHidden?.Invoke(beatmap);
@@ -136,6 +140,7 @@ namespace osu.Game.Beatmaps
                 Refresh(ref beatmap, Beatmaps);
 
                 if (!beatmap.Hidden) return false;
+
                 beatmap.Hidden = false;
             }
 
@@ -155,7 +160,9 @@ namespace osu.Game.Beatmaps
                                        .Where(query)
                                        .Include(s => s.Beatmaps).ThenInclude(b => b.Metadata)
                                        .Include(s => s.Beatmaps).ThenInclude(b => b.BaseDifficulty)
-                                       .Include(s => s.Metadata);
+                                       .Include(s => s.Metadata).ToList();
+
+                if (!purgeable.Any()) return;
 
                 // metadata is M-N so we can't rely on cascades
                 context.BeatmapMetadata.RemoveRange(purgeable.Select(s => s.Metadata));

osu.Game/Database/DatabaseBackedStore.cs

@@ -34,10 +34,7 @@ namespace osu.Game.Database
                 var id = obj.ID;
                 var foundObject = lookupSource?.SingleOrDefault(t => t.ID == id) ?? context.Find<T>(id);
                 if (foundObject != null)
-                {
                     obj = foundObject;
-                    context.Entry(obj).Reload();
-                }
                 else
                     context.Add(obj);
             }

osu.Game/Database/DatabaseContextFactory.cs

@@ -1,6 +1,7 @@
 // Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
 // Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
 
+using System.Diagnostics;
 using System.Threading;
 using osu.Framework.Platform;
 
@@ -18,6 +19,7 @@ namespace osu.Game.Database
 
         private OsuDbContext writeContext;
 
+        private bool currentWriteDidWrite;
         private volatile int currentWriteUsages;
 
         public DatabaseContextFactory(GameHost host)
@@ -38,25 +40,42 @@ namespace osu.Game.Database
         /// <returns>A usage containing a usable context.</returns>
         public DatabaseWriteUsage GetForWrite()
         {
-            lock (writeLock)
+            Monitor.Enter(writeLock);
-            {
+
-                var usage = new DatabaseWriteUsage(writeContext ?? (writeContext = threadContexts.Value), usageCompleted);
+            Trace.Assert(currentWriteUsages == 0, "Database writes in a bad state");
             Interlocked.Increment(ref currentWriteUsages);
-                return usage;
+
-            }
+            return new DatabaseWriteUsage(writeContext ?? (writeContext = threadContexts.Value), usageCompleted);
         }
 
         private void usageCompleted(DatabaseWriteUsage usage)
         {
             int usages = Interlocked.Decrement(ref currentWriteUsages);
-            if (usages == 0)
+
+            try
+            {
+                currentWriteDidWrite |= usage.PerformedWrite;
+
+                if (usages > 0) return;
+
+
+                if (currentWriteDidWrite)
                 {
                     writeContext.Dispose();
-                writeContext = null;
+                    currentWriteDidWrite = false;
 
                     // once all writes are complete, we want to refresh thread-specific contexts to make sure they don't have stale local caches.
                     recycleThreadContexts();
                 }
+
+                // always set to null (even when a write didn't occur) so we get the correct thread context on next write request.
+                writeContext = null;
+
+            }
+            finally
+            {
+                Monitor.Exit(writeLock);
+            }
         }
 
         private void recycleThreadContexts() => threadContexts = new ThreadLocal<OsuDbContext>(CreateContext);

osu.Game/Database/DatabaseWriteUsage.cs

@@ -19,10 +19,28 @@ namespace osu.Game.Database
             usageCompleted = onCompleted;
         }
 
+        public bool PerformedWrite { get; private set; }
+
+        private bool isDisposed;
+
+        protected void Dispose(bool disposing)
+        {
+            if (isDisposed) return;
+            isDisposed = true;
+
+            PerformedWrite |= Context.SaveChanges(transaction) > 0;
+            usageCompleted?.Invoke(this);
+        }
+
         public void Dispose()
         {
-            Context.SaveChanges(transaction);
+            Dispose(true);
-            usageCompleted?.Invoke(this);
+            GC.SuppressFinalize(this);
+        }
+
+        ~DatabaseWriteUsage()
+        {
+            Dispose(false);
         }
     }
 }

osu.Game/Database/OsuDbContext.cs

@@ -111,7 +111,7 @@ namespace osu.Game.Database
         public int SaveChanges(IDbContextTransaction transaction = null)
         {
             var ret = base.SaveChanges();
-            transaction?.Commit();
+            if (ret > 0) transaction?.Commit();
             return ret;
         }
 

osu.Game/IO/FileStore.cs

@@ -30,11 +30,9 @@ namespace osu.Game.IO
         {
             using (var usage = ContextFactory.GetForWrite())
             {
-                var context = usage.Context;
-
                 string hash = data.ComputeSHA2Hash();
 
-                var existing = context.FileInfo.FirstOrDefault(f => f.Hash == hash);
+                var existing = usage.Context.FileInfo.FirstOrDefault(f => f.Hash == hash);
 
                 var info = existing ?? new FileInfo { Hash = hash };
 
@@ -60,6 +58,8 @@ namespace osu.Game.IO
 
         public void Reference(params FileInfo[] files)
         {
+            if (files.Length == 0) return;
+
             using (var usage = ContextFactory.GetForWrite())
             {
                 var context = usage.Context;
@@ -75,9 +75,12 @@ namespace osu.Game.IO
 
         public void Dereference(params FileInfo[] files)
         {
+            if (files.Length == 0) return;
+
             using (var usage = ContextFactory.GetForWrite())
             {
                 var context = usage.Context;
+
                 foreach (var f in files.GroupBy(f => f.ID))
                 {
                     var refetch = context.FileInfo.Find(f.Key);

osu.Game/Input/KeyBindingStore.cs

@@ -36,8 +36,6 @@ namespace osu.Game.Input
         {
             using (var usage = ContextFactory.GetForWrite())
             {
-                var context = usage.Context;
-
                 // compare counts in database vs defaults
                 foreach (var group in defaults.GroupBy(k => k.Action))
                 {
@@ -49,7 +47,7 @@ namespace osu.Game.Input
 
                     foreach (var insertable in group.Skip(count).Take(aimCount - count))
                         // insert any defaults which are missing.
-                        context.DatabasedKeyBinding.Add(new DatabasedKeyBinding
+                        usage.Context.DatabasedKeyBinding.Add(new DatabasedKeyBinding
                         {
                             KeyCombination = insertable.KeyCombination,
                             Action = insertable.Action,
@@ -75,6 +73,10 @@ namespace osu.Game.Input
             {
                 var dbKeyBinding = (DatabasedKeyBinding)keyBinding;
                 Refresh(ref dbKeyBinding);
+
+                if (dbKeyBinding.KeyCombination.Equals(keyBinding.KeyCombination))
+                    return;
+
                 dbKeyBinding.KeyCombination = keyBinding.KeyCombination;
             }