Added RunParallel extension method for enumerables

BepInEx/ThreadingHelper.cs

@@ -1,6 +1,8 @@
 using System;
+using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;
+using System.Reflection;
 using System.Threading;
 using BepInEx.Logging;
 using UnityEngine;
@@ -142,7 +144,7 @@ namespace BepInEx
 		{
 			var invokeResult = (InvokeResult)result;
 			invokeResult.AsyncWaitHandle.WaitOne();
-			
+
 			if (invokeResult.ExceptionThrown)
 				throw (Exception)invokeResult.AsyncState;
 			return invokeResult.AsyncState;
@@ -170,7 +172,7 @@ namespace BepInEx
 
 			public void Finish(object result, bool completedSynchronously)
 			{
-                AsyncState = result;
+				AsyncState = result;
 				CompletedSynchronously = completedSynchronously;
 				IsCompleted = true;
 				((EventWaitHandle)AsyncWaitHandle).Set();
@@ -185,4 +187,103 @@ namespace BepInEx
 
 		#endregion
 	}
+
+	/// <summary>
+	/// Convenience extensions for utilizing multiple threads and using the <see cref="ThreadingHelper"/>.
+	/// </summary>
+	public static class ThreadingExtensions
+	{
+		/// <inheritdoc cref="RunParallel{TIn,TOut}(IList{TIn},Func{TIn,TOut},int)"/>
+		public static IEnumerable<TOut> RunParallel<TIn, TOut>(this IEnumerable<TIn> data, Func<TIn, TOut> work, int workerCount = -1)
+		{
+			foreach (var result in RunParallel(data.ToList(), work))
+				yield return result;
+		}
+
+		/// <summary>
+		/// Apply a function to a collection of data by spreading the work on multiple threads.
+		/// Outputs of the functions are returned to the current thread and yielded one by one.
+		/// </summary>
+		/// <typeparam name="TIn">Type of the input values.</typeparam>
+		/// <typeparam name="TOut">Type of the output values.</typeparam>
+		/// <param name="data">Input values for the work function.</param>
+		/// <param name="work">Function to apply to the data on multiple threads at once.</param>
+		/// <param name="workerCount">Number of worker threads. By default SystemInfo.processorCount is used.</param>
+		/// <exception cref="TargetInvocationException">An exception was thrown inside one of the threads, and the operation was aborted.</exception>
+		/// <exception cref="ArgumentException">Need at least 1 workerCount.</exception>
+		public static IEnumerable<TOut> RunParallel<TIn, TOut>(this IList<TIn> data, Func<TIn, TOut> work, int workerCount = -1)
+		{
+			if (workerCount < 0)
+				workerCount = Mathf.Max(2, SystemInfo.processorCount);
+			else if (workerCount == 0)
+				throw new ArgumentException("Need at least 1 worker", nameof(workerCount));
+
+			var perThreadCount = Mathf.CeilToInt(data.Count / (float)workerCount);
+			var doneCount = 0;
+
+			var lockObj = new object();
+			var are = new ManualResetEvent(false);
+			IEnumerable<TOut> doneItems = null;
+			Exception exceptionThrown = null;
+
+			// Start threads to process the data
+			for (var i = 0; i < workerCount; i++)
+			{
+				int first = i * perThreadCount;
+				int last = Mathf.Min(first + perThreadCount, data.Count);
+				ThreadPool.QueueUserWorkItem(
+					_ =>
+					{
+						var results = new List<TOut>(perThreadCount);
+
+						try
+						{
+							for (int dataIndex = first; dataIndex < last; dataIndex++)
+							{
+								if (exceptionThrown != null) break;
+								results.Add(work(data[dataIndex]));
+							}
+						}
+						catch (Exception ex)
+						{
+							exceptionThrown = ex;
+						}
+
+						lock (lockObj)
+						{
+							doneItems = doneItems == null ? results : results.Concat(doneItems);
+							doneCount++;
+							are.Set();
+						}
+					});
+			}
+
+			// Main thread waits for results and returns them until all threads finish
+			while (true)
+			{
+				are.WaitOne();
+
+				IEnumerable<TOut> toOutput;
+				bool isDone;
+				lock (lockObj)
+				{
+					toOutput = doneItems;
+					doneItems = null;
+					isDone = doneCount == workerCount;
+				}
+
+				if (toOutput != null)
+				{
+					foreach (var doneItem in toOutput)
+						yield return doneItem;
+				}
+
+				if (isDone)
+					break;
+			}
+
+			if (exceptionThrown != null)
+				throw new TargetInvocationException("An exception was thrown inside one of the threads", exceptionThrown);
+		}
+	}
 }