From ae40ae7abc9b2e089037505d09d82583520f7bd2 Mon Sep 17 00:00:00 2001
From: Anairkoen Schno <aaron.cirr.com@gmail.com>
Date: Thu, 16 Jan 2020 23:25:25 -0600
Subject: [PATCH] Documented UnityMainThreadTaskScheduler

---
 .../Async/UnityMainThreadTaskScheduler.cs     | 105 +++++++++++++++++-
 1 file changed, 101 insertions(+), 4 deletions(-)

diff --git a/IPA.Loader/Utilities/Async/UnityMainThreadTaskScheduler.cs b/IPA.Loader/Utilities/Async/UnityMainThreadTaskScheduler.cs
index f0b97184..15ec96ea 100644
--- a/IPA.Loader/Utilities/Async/UnityMainThreadTaskScheduler.cs
+++ b/IPA.Loader/Utilities/Async/UnityMainThreadTaskScheduler.cs
@@ -2,6 +2,7 @@
 using System.Collections;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Text;
 using System.Threading;
@@ -9,8 +10,15 @@ using System.Threading.Tasks;
 
 namespace IPA.Utilities.Async
 {
+    /// <summary>
+    /// A task scheduler that runs tasks on the Unity main thread via coroutines.
+    /// </summary>
     public class UnityMainThreadTaskScheduler : TaskScheduler, IDisposable
     {
+        /// <summary>
+        /// Gets the default main thread scheduler that is managed by BSIPA.
+        /// </summary>
+        /// <value>a scheduler that is managed by BSIPA</value>
         public static new TaskScheduler Default { get; } = new UnityMainThreadTaskScheduler();
 
         private readonly ConcurrentDictionary<QueueItem, Task> tasks = new ConcurrentDictionary<QueueItem, Task>();
@@ -33,41 +41,113 @@ namespace IPA.Utilities.Async
             public bool Equals(QueueItem other) => other.Index == Index || other.Task == Task;
         }
 
+        /// <summary>
+        /// Gets whether or not this scheduler is currently executing tasks.
+        /// </summary>
+        /// <value><see langword="true"/> if the scheduler is running, <see langword="false"/> otherwise</value>
         public bool IsRunning { get; private set; } = false;
 
-        public int YieldAfterTasks { get; set; } = 4;
+        /// <summary>
+        /// Gets whether or not this scheduler is in the process of shutting down.
+        /// </summary>
+        /// <value><see langword="true"/> if the scheduler is shutting down, <see langword="false"/> otherwise</value>
+        public bool Cancelling { get; private set; } = false;
+
+        private int yieldAfterTasks = 64;
+        /// <summary>
+        /// Gets or sets the number of tasks to execute before yielding back to Unity.
+        /// </summary>
+        /// <value>the number of tasks to execute per resume</value>
+        public int YieldAfterTasks
+        {
+            get => yieldAfterTasks;
+            set
+            {
+                ThrowIfDisposed();
+                if (value < 1) 
+                    throw new ArgumentException("Value cannot be less than 1", nameof(value));
+                yieldAfterTasks = value;
+            }
+        }
+
+        private TimeSpan yieldAfterTime = TimeSpan.FromMilliseconds(.5); // auto-yield if more than half a millis has passed by default
+        /// <summary>
+        /// Gets or sets the amount of time to execute tasks for before yielding back to Unity. Default is 0.5ms.
+        /// </summary>
+        /// <value>the amount of time to execute tasks for before yielding back to Unity</value>
+        public TimeSpan YieldAfterTime
+        {
+            get => yieldAfterTime;
+            set
+            {
+                ThrowIfDisposed();
+                if (value <= TimeSpan.Zero)
+                    throw new ArgumentException("Value must be greater than zero", nameof(value));
+                yieldAfterTime = value;
+            }
+        }
 
+        /// <summary>
+        /// When used as a Unity coroutine, runs the scheduler. Otherwise, this is an invalid call.
+        /// </summary>
+        /// <returns>a Unity coroutine</returns>
+        /// <exception cref="ObjectDisposedException">if this scheduler is disposed</exception>
+        /// <exception cref="InvalidOperationException">if the scheduler is already running</exception>
         public IEnumerator Coroutine()
         {
             ThrowIfDisposed();
 
+            if (IsRunning)
+                throw new InvalidOperationException("Scheduler already running");
+
+            Cancelling = false;
             IsRunning = true;
             yield return null; // yield immediately
 
+            var sw = new Stopwatch();
+
             try
             {
-                while (true)
+                while (!Cancelling)
                 {
                     if (queuePosition < queueEndPosition)
                     {
                         var yieldAfter = YieldAfterTasks;
-                        for (int i = 0; i < yieldAfter && queuePosition < queueEndPosition; i++)
+                        sw.Start();
+                        for (int i = 0; i < yieldAfter && queuePosition < queueEndPosition 
+                                                       && sw.Elapsed < YieldAfterTime; i++)
                         {
                             if (tasks.TryRemove(new QueueItem { Index = Interlocked.Increment(ref queuePosition) }, out var task))
                                 TryExecuteTask(task); // we succesfully removed the task
                             else
                                 i++; // we didn't
                         }
+                        sw.Reset();
                     }
                     yield return null;
                 }
             }
             finally
             {
+                sw.Reset();
                 IsRunning = false;
             }
         }
 
+        /// <summary>
+        /// Cancels the scheduler. If the scheduler is currently executing tasks, that batch will finish first.
+        /// All remaining tasks will be left in the queue.
+        /// </summary>
+        /// <exception cref="ObjectDisposedException">if this scheduler is disposed</exception>
+        /// <exception cref="InvalidOperationException">if the scheduler is not running</exception>
+        public void Cancel()
+        {
+            ThrowIfDisposed();
+
+            if (!IsRunning) throw new InvalidOperationException("The scheduler is not running");
+            Cancelling = true;
+        }
+
         /// <summary>
         /// Throws a <see cref="NotSupportedException"/>.
         /// </summary>
@@ -79,6 +159,12 @@ namespace IPA.Utilities.Async
             throw new NotSupportedException();
         }
 
+        /// <summary>
+        /// Queues a given <see cref="Task"/> to this scheduler. The <see cref="Task"/> <i>must></i> be
+        /// scheduled for this <see cref="TaskScheduler"/> by the runtime.
+        /// </summary>
+        /// <param name="task">the <see cref="Task"/> to queue</param>
+        /// <exception cref="ObjectDisposedException">Thrown if this object has already been disposed.</exception>
         protected override void QueueTask(Task task)
         {
             ThrowIfDisposed();
@@ -86,6 +172,17 @@ namespace IPA.Utilities.Async
             tasks.TryAdd(new QueueItem(Interlocked.Increment(ref queueEndPosition), task), task);
         }
 
+        /// <summary>
+        /// Rejects any attempts to execute a task inline.
+        /// </summary>
+        /// <remarks>
+        /// This task scheduler <i>always</i> runs its tasks on the thread that it manages, therefore it doesn't
+        /// make sense to run it inline.
+        /// </remarks>
+        /// <param name="task">the task to attempt to execute</param>
+        /// <param name="taskWasPreviouslyQueued">whether the task was previously queued to this scheduler</param>
+        /// <returns><see langword="false"/></returns>
+        /// <exception cref="ObjectDisposedException">Thrown if this object has already been disposed.</exception>
         protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
         {
             ThrowIfDisposed();
@@ -114,7 +211,7 @@ namespace IPA.Utilities.Async
             {
                 if (disposing)
                 {
-                    // TODO: dispose managed state (managed objects).
+
                 }
 
                 disposedValue = true;