Improve InvokeOnMainThread mechanism

Add documentation to make the invoke mechanism easier to understand
Make it clear in documentation that code is invoked synchronously
Use Action and Func<T> for minimizing the amount of code to write
Use type parameter T to automatically adjust return value type
Throw exceptions on the calling thread, not the main thread

MinecraftClient/ChatBot.cs

@@ -1402,12 +1402,13 @@ namespace MinecraftClient
         ///     Console.WriteLine("10 seconds has passed");
         /// }), 100);
         /// </example>
-        protected void ScheduleTaskDelayed(Delegate task, int delayTicks = 0)
+        // TODO: Adapt to new IMinecraftComHandler API
+        /*protected void ScheduleTaskDelayed(Delegate task, int delayTicks = 0)
         {
             if (delayTicks <= 0)
             {
                 // Immediately schedule to run on next update
-                Handler.ScheduleTask(task);
+                Handler.InvokeOnMainThread(task);
             }
             else
             {
@@ -1416,17 +1417,19 @@ namespace MinecraftClient
                     delayTasks.Add(new DelayedTask(task, delayTicks));
                 }
             }
-        }
+        }*/
 
         /// <summary>
         /// Schedule a task to run on main thread.
         /// </summary>
         /// <param name="task">Task to run</param>
         /// <returns>Any value returned from the task</returns>
+        // TODO: Adapt to new IMinecraftComHandler API
+        /*
         protected object ScheduleTask(Delegate task)
         {
-            return Handler.ScheduleTask(task);
-        }
+            return Handler.InvokeOnMainThread(task);
+        }*/
 
         /// <summary>
         /// Command runner definition.

MinecraftClient/McClient.cs

@@ -32,7 +32,7 @@ namespace MinecraftClient
         private Queue<string> chatQueue = new Queue<string>();
         private static DateTime nextMessageSendTime = DateTime.MinValue;
 
-        private Queue<TaskWithResult> threadTasks = new Queue<TaskWithResult>();
+        private Queue<Action> threadTasks = new Queue<Action>();
         private object threadTasksLock = new object();
 
         private readonly List<ChatBot> bots = new List<ChatBot>();
@@ -302,7 +302,6 @@ namespace MinecraftClient
 
         /// <summary>
         /// Allows the user to send chat messages, commands, and leave the server.
-        /// Enqueue text typed in the command prompt for processing on the main thread.
         /// </summary>
         private void CommandPrompt()
         {
@@ -312,7 +311,7 @@ namespace MinecraftClient
                 while (client.Client.Connected)
                 {
                     string text = ConsoleIO.ReadLine();
-                    ScheduleTask(new Action(() => { HandleCommandPromptText(text); }));
+                    InvokeOnMainThread(() => HandleCommandPromptText(text));
                 }   
             }
             catch (IOException) { }
@@ -641,14 +640,12 @@ namespace MinecraftClient
                     SendRespawnPacket();
             }
 
-            
             lock (threadTasksLock)
             {
                 while (threadTasks.Count > 0)
                 {
-                    var taskToRun = threadTasks.Dequeue();
-                    taskToRun.Execute();
-                    taskToRun.Release();
+                    Action taskToRun = threadTasks.Dequeue();
+                    taskToRun();
                 }
             }
         }
@@ -696,28 +693,43 @@ namespace MinecraftClient
         }
 
         /// <summary>
-        /// Schedule a task to run on the main thread
+        /// Invoke a task on the main thread, wait for completion and retrieve return value.
         /// </summary>
-        /// <param name="task">Task to run</param>
-        /// <returns>Any result returned from delegate</returns>
-        public object ScheduleTask(Delegate task)
+        /// <param name="task">Task to run with any type or return value</param>
+        /// <returns>Any result returned from task, result type is inferred from the task</returns>
+        /// <example>bool result = InvokeOnMainThread(methodThatReturnsAbool);</example>
+        /// <example>bool result = InvokeOnMainThread(() => methodThatReturnsAbool(argument));</example>
+        /// <example>int result = InvokeOnMainThread(() => { yourCode(); return 42; });</example>
+        /// <typeparam name="T">Type of the return value</typeparam>
+        public T InvokeOnMainThread<T>(Func<T> task)
         {
             if (!InvokeRequired())
             {
-                return task.DynamicInvoke();
+                return task();
             }
             else
             {
-                var taskAndResult = new TaskWithResult(task);
+                TaskWithResult<T> taskWithResult = new TaskWithResult<T>(task);
                 lock (threadTasksLock)
                 {
-                    threadTasks.Enqueue(taskAndResult);
+                    threadTasks.Enqueue(taskWithResult.ExecuteSynchronously);
                 }
-                taskAndResult.Block();
-                return taskAndResult.Result;
+                return taskWithResult.WaitGetResult();
             }
         }
 
+        /// <summary>
+        /// Invoke a task on the main thread and wait for completion
+        /// </summary>
+        /// <param name="task">Task to run without return value</param>
+        /// <example>InvokeOnMainThread(methodThatReturnsNothing);</example>
+        /// <example>InvokeOnMainThread(() => methodThatReturnsNothing(argument));</example>
+        /// <example>InvokeOnMainThread(() => { yourCode(); });</example>
+        public void InvokeOnMainThread(Action task)
+        {
+            InvokeOnMainThread(() => { task(); return true; });
+        }
+
         /// <summary>
         /// Check if calling thread is main thread or other thread
         /// </summary>

MinecraftClient/Protocol/Handlers/Protocol18.cs

@@ -423,10 +423,9 @@ namespace MinecraftClient.Protocol.Handlers
                                 int compressedDataSize = dataTypes.ReadNextInt(packetData);
                                 byte[] compressed = dataTypes.ReadData(compressedDataSize, packetData);
                                 byte[] decompressed = ZlibUtils.Decompress(compressed);
-                                new Task(new Action(() =>
-                                {
+                                new Thread(() => {
                                     pTerrain.ProcessChunkColumnData(chunkX, chunkZ, chunkMask, addBitmap, currentDimension == 0, chunksContinuous, currentDimension, new Queue<byte>(decompressed));
-                                })).Start();
+                                }).Start();
                             }
                             else
                             {
@@ -450,10 +449,9 @@ namespace MinecraftClient.Protocol.Handlers
                                     else dataTypes.ReadData(1024 * 4, packetData); // Biomes - 1.15 and above
                                 }
                                 int dataSize = dataTypes.ReadNextVarInt(packetData);
-                                new Task(new Action(() =>
-                                {
+                                new Thread(() => {
                                     pTerrain.ProcessChunkColumnData(chunkX, chunkZ, chunkMask, 0, false, chunksContinuous, currentDimension, packetData);
-                                })).Start();
+                                }).Start();
                             }
                         }
                         break;

MinecraftClient/Protocol/Handlers/Protocol18Terrain.cs

@@ -162,12 +162,12 @@ namespace MinecraftClient.Protocol.Handlers
                         }
 
                         //We have our chunk, save the chunk into the world
-                        handler.ScheduleTask(new Action(() => 
+                        handler.InvokeOnMainThread(() =>
                         {
                             if (handler.GetWorld()[chunkX, chunkZ] == null)
                                 handler.GetWorld()[chunkX, chunkZ] = new ChunkColumn();
                             handler.GetWorld()[chunkX, chunkZ][chunkY] = chunk;
-                        }));
+                        });
 
                         //Pre-1.14 Lighting data
                         if (protocolversion < Protocol18Handler.MC114Version)
@@ -192,10 +192,10 @@ namespace MinecraftClient.Protocol.Handlers
                 if (chunksContinuous && chunkMask == 0)
                 {
                     //Unload the entire chunk column
-                    handler.ScheduleTask(new Action(() =>
+                    handler.InvokeOnMainThread(() =>
                     {
                         handler.GetWorld()[chunkX, chunkZ] = null;
-                    }));
+                    });
                 }
                 else
                 {
@@ -214,12 +214,12 @@ namespace MinecraftClient.Protocol.Handlers
                                         chunk[blockX, blockY, blockZ] = new Block(queue.Dequeue());
 
                             //We have our chunk, save the chunk into the world
-                            handler.ScheduleTask(new Action(() =>
+                            handler.InvokeOnMainThread(() =>
                             {
                                 if (handler.GetWorld()[chunkX, chunkZ] == null)
                                     handler.GetWorld()[chunkX, chunkZ] = new ChunkColumn();
                                 handler.GetWorld()[chunkX, chunkZ][chunkY] = chunk;
-                            }));
+                            });
                         }
                     }
 
@@ -248,10 +248,10 @@ namespace MinecraftClient.Protocol.Handlers
                 if (chunksContinuous && chunkMask == 0)
                 {
                     //Unload the entire chunk column
-                    handler.ScheduleTask(new Action(() =>
+                    handler.InvokeOnMainThread(() =>
                     {
                         handler.GetWorld()[chunkX, chunkZ] = null;
-                    }));
+                    });
                 }
                 else
                 {
@@ -297,12 +297,12 @@ namespace MinecraftClient.Protocol.Handlers
                                     for (int blockX = 0; blockX < Chunk.SizeX; blockX++)
                                         chunk[blockX, blockY, blockZ] = new Block(blockTypes.Dequeue(), blockMeta.Dequeue());
 
-                            handler.ScheduleTask(new Action(() =>
+                            handler.InvokeOnMainThread(() =>
                             {
                                 if (handler.GetWorld()[chunkX, chunkZ] == null)
                                     handler.GetWorld()[chunkX, chunkZ] = new ChunkColumn();
                                 handler.GetWorld()[chunkX, chunkZ][chunkY] = chunk;
-                            }));
+                            });
                         }
                     }
                 }

MinecraftClient/Protocol/IMinecraftComHandler.cs

@@ -41,11 +41,24 @@ namespace MinecraftClient.Protocol
         ILogger GetLogger();
 
         /// <summary>
-        /// Schedule a task to run on the main thread
+        /// Invoke a task on the main thread, wait for completion and retrieve return value.
         /// </summary>
-        /// <param name="task">Task to run</param>
-        /// <returns>Any result returned from delegate</returns>
-        object ScheduleTask(Delegate task);
+        /// <param name="task">Task to run with any type or return value</param>
+        /// <returns>Any result returned from task, result type is inferred from the task</returns>
+        /// <example>bool result = InvokeOnMainThread(methodThatReturnsAbool);</example>
+        /// <example>bool result = InvokeOnMainThread(() => methodThatReturnsAbool(argument));</example>
+        /// <example>int result = InvokeOnMainThread(() => { yourCode(); return 42; });</example>
+        /// <typeparam name="T">Type of the return value</typeparam>
+        T InvokeOnMainThread<T>(Func<T> task);
+
+        /// <summary>
+        /// Invoke a task on the main thread and wait for completion
+        /// </summary>
+        /// <param name="task">Task to run without return value</param>
+        /// <example>InvokeOnMainThread(methodThatReturnsNothing);</example>
+        /// <example>InvokeOnMainThread(() => methodThatReturnsNothing(argument));</example>
+        /// <example>InvokeOnMainThread(() => { yourCode(); });</example>
+        void InvokeOnMainThread(Action task);
 
         /// <summary>
         /// Called when a network packet received or sent

MinecraftClient/TaskWithResult.cs

@@ -6,42 +6,121 @@ using System.Threading;
 
 namespace MinecraftClient
 {
-    public class TaskWithResult
+    /// <summary>
+    /// Holds an asynchronous task with return value
+    /// </summary>
+    /// <typeparam name="T">Type of the return value</typeparam>
+    public class TaskWithResult<T>
     {
-        private Delegate Task;
-        private AutoResetEvent ResultEvent = new AutoResetEvent(false);
+        private AutoResetEvent resultEvent = new AutoResetEvent(false);
+        private Func<T> task;
+        private T result = default(T);
+        private Exception exception = null;
+        private bool taskRun = false;
+        private object taskRunLock = new object();
 
-        public object Result;
-
-        public TaskWithResult(Delegate task)
+        /// <summary>
+        /// Create a new asynchronous task with return value
+        /// </summary>
+        /// <param name="task">Delegate with return value</param>
+        public TaskWithResult(Func<T> task)
         {
-            Task = task;
+            this.task = task;
         }
 
         /// <summary>
-        /// Execute the delegate and set the <see cref="Result"/> property to the returned value
+        /// Check whether the task has finished running
         /// </summary>
-        /// <returns>Value returned from delegate</returns>
-        public object Execute()
+        public bool HasRun
         {
-            Result = Task.DynamicInvoke();
-            return Result;
+            get
+            {
+                return taskRun;
+            }
         }
 
         /// <summary>
-        /// Block the program execution
+        /// Get the task result (return value of the inner delegate)
         /// </summary>
-        public void Block()
+        /// <exception cref="System.InvalidOperationException">Thrown if the task is not finished yet</exception>
+        public T Result
         {
-            ResultEvent.WaitOne();
+            get
+            {
+                if (taskRun)
+                {
+                    return result;
+                }
+                else throw new InvalidOperationException("Attempting to retrieve the result of an unfinished task");
+            }
         }
 
         /// <summary>
-        /// Resume the program execution
+        /// Get the exception thrown by the inner delegate, if any
         /// </summary>
-        public void Release()
+        public Exception Exception
         {
-            ResultEvent.Set();
+            get
+            {
+                return exception;
+            }
+        }
+
+        /// <summary>
+        /// Execute the task in the current thread and set the <see cref="Result"/> property or <see cref=""/>to the returned value
+        /// </summary>
+        public void ExecuteSynchronously()
+        {
+            // Make sur the task will not run twice
+            lock (taskRunLock)
+            {
+                if (taskRun)
+                {
+                    throw new InvalidOperationException("Attempting to run a task twice");
+                }
+            }
+
+            // Run the task
+            try
+            {
+                result = task();
+            }
+            catch (Exception e)
+            {
+                exception = e;
+            }
+
+            // Mark task as complete and release wait event
+            lock (taskRunLock)
+            {
+                taskRun = true;
+            }
+            resultEvent.Set();
+        }
+
+        /// <summary>
+        /// Wait until the task has run from another thread and get the returned value or exception thrown by the task
+        /// </summary>
+        /// <returns>Task result once available</returns>
+        /// <exception cref="System.Exception">Any exception thrown by the task</exception>
+        public T WaitGetResult()
+        {
+            // Wait only if the result is not available yet
+            bool mustWait = false;
+            lock (taskRunLock)
+            {
+                mustWait = !taskRun;
+            }
+            if (mustWait)
+            {
+                resultEvent.WaitOne();
+            }
+
+            // Receive exception from task
+            if (exception != null)
+                throw exception;
+
+            return result;
         }
     }
 }