FastParallel.cs

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using System;
using System.Threading;
 
namespace ReLogic.Threading;
 
public static class FastParallel
{
    private class RangeTask
    {
        private readonly ParallelForAction _action;
 
        private readonly int _fromInclusive;
 
        private readonly int _toExclusive;
 
        private readonly object _context;
 
        private readonly CountdownEvent _countdown;
 
        public RangeTask(ParallelForAction action, int fromInclusive, int toExclusive, object context, CountdownEvent countdown)
        {
            _action = action;
            _fromInclusive = fromInclusive;
            _toExclusive = toExclusive;
            _context = context;
            _countdown = countdown;
        }
 
        public void Invoke()
        {
            try
            {
                if (_fromInclusive != _toExclusive)
                {
                    _action(_fromInclusive, _toExclusive, _context);
                }
            }
            finally
            {
                _countdown.Signal();
            }
        }
    }
 
    public static bool ForceTasksOnCallingThread { get; set; }
 
    static FastParallel()
    {
        ForceTasksOnCallingThread = false;
    }
 
    public static void For(int fromInclusive, int toExclusive, ParallelForAction callback, object context = null)
    {
        int num = toExclusive - fromInclusive;
        if (num == 0)
        {
            return;
        }
        int num2 = Math.Min(Math.Max(1, Environment.ProcessorCount + 1 - 1 - 1), num);
        if (ForceTasksOnCallingThread)
        {
            num2 = 1;
        }
        int num3 = num / num2;
        int num4 = num % num2;
        CountdownEvent countdownEvent = new CountdownEvent(num2);
        int num5 = toExclusive;
        for (int num6 = num2 - 1; num6 >= 0; num6--)
        {
            int num7 = num3;
            if (num6 < num4)
            {
                num7++;
            }
            num5 -= num7;
            int num8 = num5;
            int toExclusive2 = num8 + num7;
            RangeTask rangeTask = new RangeTask(callback, num8, toExclusive2, context, countdownEvent);
            if (num6 < 1)
            {
                InvokeTask(rangeTask);
            }
            else
            {
                ThreadPool.QueueUserWorkItem(InvokeTask, rangeTask);
            }
        }
        if (countdownEvent.Wait(10000))
        {
            return;
        }
        ThreadPool.GetAvailableThreads(out var workerThreads, out var _);
        throw new Exception($"Fatal Deadlock in FastParallelFor. pending: {ThreadPool.PendingWorkItemCount}. avail: {workerThreads}");
    }
 
    private static void InvokeTask(object context)
    {
        ((RangeTask)context).Invoke();
    }
}