fix errors due to async threads creating content managers

docs/release-notes.md

@@ -6,6 +6,7 @@
 * For players:
   * SMAPI now prevents mods from crashing the game with invalid schedule data.
   * Updated minimum game version (1.4 → 1.4.1).
+  * Fixed 'collection was modified' error when returning to title in rare cases.
 
 ## 3.1
 Released 05 January 2019 for Stardew Valley 1.4 or later.

src/SMAPI/Framework/ContentCoordinator.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.IO;
 using System.Linq;
+using System.Threading;
 using Microsoft.Xna.Framework.Content;
 using StardewModdingAPI.Framework.Content;
 using StardewModdingAPI.Framework.ContentManagers;
@@ -48,6 +49,10 @@ namespace StardewModdingAPI.Framework
         /// <summary>Whether the content coordinator has been disposed.</summary>
         private bool IsDisposed;
 
+        /// <summary>A lock used to prevent asynchronous changes to the content manager list.</summary>
+        /// <remarks>The game may adds content managers in asynchronous threads (e.g. when populating the load screen).</remarks>
+        private readonly ReaderWriterLockSlim ContentManagerLock = new ReaderWriterLockSlim();
+
 
         /*********
         ** Accessors
@@ -95,10 +100,13 @@ namespace StardewModdingAPI.Framework
         /// <summary>Get a new content manager which handles reading files from the game content folder with support for interception.</summary>
         /// <param name="name">A name for the mod manager. Not guaranteed to be unique.</param>
         public GameContentManager CreateGameContentManager(string name)
+        {
+            return this.ContentManagerLock.InWriteLock(() =>
             {
                 GameContentManager manager = new GameContentManager(name, this.MainContentManager.ServiceProvider, this.MainContentManager.RootDirectory, this.MainContentManager.CurrentCulture, this, this.Monitor, this.Reflection, this.OnDisposing, this.OnLoadingFirstAsset);
                 this.ContentManagers.Add(manager);
                 return manager;
+            });
         }
 
         /// <summary>Get a new content manager which handles reading files from a SMAPI mod folder with support for unpacked files.</summary>
@@ -106,6 +114,8 @@ namespace StardewModdingAPI.Framework
         /// <param name="rootDirectory">The root directory to search for content (or <c>null</c> for the default).</param>
         /// <param name="gameContentManager">The game content manager used for map tilesheets not provided by the mod.</param>
         public ModContentManager CreateModContentManager(string name, string rootDirectory, IContentManager gameContentManager)
+        {
+            return this.ContentManagerLock.InWriteLock(() =>
             {
                 ModContentManager manager = new ModContentManager(
                     name: name,
@@ -121,6 +131,7 @@ namespace StardewModdingAPI.Framework
                 );
                 this.ContentManagers.Add(manager);
                 return manager;
+            });
         }
 
         /// <summary>Get the current content locale.</summary>
@@ -131,9 +142,12 @@ namespace StardewModdingAPI.Framework
 
         /// <summary>Perform any cleanup needed when the locale changes.</summary>
         public void OnLocaleChanged()
+        {
+            this.ContentManagerLock.InReadLock(() =>
             {
                 foreach (IContentManager contentManager in this.ContentManagers)
                     contentManager.OnLocaleChanged();
+            });
         }
 
         /// <summary>Get whether this asset is mapped to a mod folder.</summary>
@@ -178,6 +192,8 @@ namespace StardewModdingAPI.Framework
         /// <param name="contentManagerID">The unique name for the content manager which should load this asset.</param>
         /// <param name="relativePath">The internal SMAPI asset key.</param>
         public T LoadManagedAsset<T>(string contentManagerID, string relativePath)
+        {
+            return this.ContentManagerLock.InReadLock(() =>
             {
                 // get content manager
                 IContentManager contentManager = this.ContentManagers.FirstOrDefault(p => p.IsNamespaced && p.Name == contentManagerID);
@@ -186,6 +202,7 @@ namespace StardewModdingAPI.Framework
 
                 // get fresh asset
                 return contentManager.Load<T>(relativePath, this.DefaultLanguage, useCache: false);
+            });
         }
 
         /// <summary>Purge matched assets from the cache.</summary>
@@ -207,6 +224,8 @@ namespace StardewModdingAPI.Framework
         /// <param name="dispose">Whether to dispose invalidated assets. This should only be <c>true</c> when they're being invalidated as part of a dispose, to avoid crashing the game.</param>
         /// <returns>Returns the invalidated asset names.</returns>
         public IEnumerable<string> InvalidateCache(Func<string, Type, bool> predicate, bool dispose = false)
+        {
+            return this.ContentManagerLock.InReadLock(() =>
             {
                 // invalidate cache & track removed assets
                 IDictionary<string, ISet<object>> removedAssets = new Dictionary<string, ISet<object>>(StringComparer.InvariantCultureIgnoreCase);
@@ -230,6 +249,7 @@ namespace StardewModdingAPI.Framework
                     this.Monitor.Log("Invalidated 0 cache entries.", LogLevel.Trace);
 
                 return removedAssets.Keys;
+            });
         }
 
         /// <summary>Dispose held resources.</summary>
@@ -244,6 +264,8 @@ namespace StardewModdingAPI.Framework
                 contentManager.Dispose();
             this.ContentManagers.Clear();
             this.MainContentManager = null;
+
+            this.ContentManagerLock.Dispose();
         }
 
 
@@ -257,7 +279,10 @@ namespace StardewModdingAPI.Framework
             if (this.IsDisposed)
                 return;
 
+            this.ContentManagerLock.InWriteLock(() =>
+            {
                 this.ContentManagers.Remove(contentManager);
+            });
         }
     }
 }

src/SMAPI/Framework/InternalExtensions.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Reflection;
+using System.Threading;
 using Microsoft.Xna.Framework.Graphics;
 using StardewModdingAPI.Framework.Events;
 using StardewModdingAPI.Framework.Reflection;
@@ -83,6 +84,75 @@ namespace StardewModdingAPI.Framework
             return exception;
         }
 
+        /****
+        ** ReaderWriterLockSlim
+        ****/
+        /// <summary>Run code within a read lock.</summary>
+        /// <param name="lock">The lock to set.</param>
+        /// <param name="action">The action to perform.</param>
+        public static void InReadLock(this ReaderWriterLockSlim @lock, Action action)
+        {
+            @lock.EnterReadLock();
+            try
+            {
+                action();
+            }
+            finally
+            {
+                @lock.ExitReadLock();
+            }
+        }
+
+        /// <summary>Run code within a read lock.</summary>
+        /// <typeparam name="TReturn">The action's return value.</typeparam>
+        /// <param name="lock">The lock to set.</param>
+        /// <param name="action">The action to perform.</param>
+        public static TReturn InReadLock<TReturn>(this ReaderWriterLockSlim @lock, Func<TReturn> action)
+        {
+            @lock.EnterReadLock();
+            try
+            {
+                return action();
+            }
+            finally
+            {
+                @lock.ExitReadLock();
+            }
+        }
+
+        /// <summary>Run code within a write lock.</summary>
+        /// <param name="lock">The lock to set.</param>
+        /// <param name="action">The action to perform.</param>
+        public static void InWriteLock(this ReaderWriterLockSlim @lock, Action action)
+        {
+            @lock.EnterWriteLock();
+            try
+            {
+                action();
+            }
+            finally
+            {
+                @lock.ExitWriteLock();
+            }
+        }
+
+        /// <summary>Run code within a write lock.</summary>
+        /// <typeparam name="TReturn">The action's return value.</typeparam>
+        /// <param name="lock">The lock to set.</param>
+        /// <param name="action">The action to perform.</param>
+        public static TReturn InWriteLock<TReturn>(this ReaderWriterLockSlim @lock, Func<TReturn> action)
+        {
+            @lock.EnterWriteLock();
+            try
+            {
+                return action();
+            }
+            finally
+            {
+                @lock.ExitWriteLock();
+            }
+        }
+
         /****
         ** Sprite batch
         ****/