C# Parallel foreach Parallel Source array was not long enough. Check srcIndex and length, Destinatio

//Index was outside the bounds of the array.

//Source array was not long enough. Check srcIndex and length, and the array's lower bounds

//
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp135
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            ConvertAAndB();
        }

        void ConvertAAndB()
        {
            System.Diagnostics.Stopwatch watch = new System.Diagnostics.Stopwatch();
            watch.Start();
            List<AModel> modelAList = new List<AModel>();
            for(int i=0;i<200000;i++)
            {
                modelAList.Add(new AModel
                {
                    Id = i + 1,
                    Name = $"Name_{i + 1}",
                    Author = $"Author_{i + 1}",
                    Title = $"Title_{i + 1}",
                    ISBN = $"ISBN_{i + 1}",
                    Topic = $"Topic_{i + 1}"
                });
            }
            watch.Stop();
            System.Diagnostics.Debug.WriteLine($"Generate :{modelAList.Count},milliseconds:{watch.ElapsedMilliseconds}");

            List<BModel> modelBList = new List<BModel>(); 
            watch.Restart();
            //for(int i=0;i<200000;i++)
            //{
            //    modelBList.Add(new BModel
            //    {
            //        Id = modelAList[i].Id,
            //        Name = modelAList[i].Name,
            //        Author = modelAList[i].Author,
            //        Title = modelAList[i].Title,
            //        Topic = modelAList[i].Topic,
            //        ISBN = modelAList[i].ISBN
            //    });
            //}
            Parallel.ForEach(modelAList, x =>
            {
                modelBList.Add(new BModel
                {
                    Id = x.Id,
                    Name = x.Name,
                    Author = x.Author,
                    Title = x.Title,
                    Topic = x.Topic,
                    ISBN = x.ISBN
                }); 
            });
            watch.Stop();
            System.Diagnostics.Debug.WriteLine($"Convert :{modelBList.Count},milliseconds:{watch.ElapsedMilliseconds}");

        }
    }

    class AModel
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Author { get; set; }
        public string Title { get; set; }
        public string ISBN { get; set; }
        public string Topic { get; set; }

    }

    class BModel
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Author { get; set; }
        public string Title { get; set; }
        public string ISBN { get; set; }
        public string Topic { get; set; }

    }
}

Plan A:

You're accessing the list by different threads, but a list is not threadsafe:

You could lock the list with:

lock(modelBList) 

{

}

Parallel.ForEach(modelAList, x =>
{
    lock(modelBList) 
    {
        modelBList.Add(new BModel
        {
            Id = x.Id,
            Name = x.Name,
            Author = x.Author,
            Title = x.Title,
            Topic = x.Topic,
            ISBN = x.ISBN
        });
    } 
});

Plan B:

ConcurrentBag

 ConcurrentBag<BModel> modelBList = new ConcurrentBag<BModel>();

void ConvertAAndB()
{
    System.Diagnostics.Stopwatch watch = new System.Diagnostics.Stopwatch();
    watch.Start();
    List<AModel> modelAList = new List<AModel>();
    for(int i=0;i<200000;i++)
    {
        modelAList.Add(new AModel
        {
            Id = i + 1,
            Name = $"Name_{i + 1}",
            Author = $"Author_{i + 1}",
            Title = $"Title_{i + 1}",
            ISBN = $"ISBN_{i + 1}",
            Topic = $"Topic_{i + 1}"
        });
    }
    watch.Stop();
    System.Diagnostics.Debug.WriteLine($"Generate :{modelAList.Count},milliseconds:{watch.ElapsedMilliseconds}");

    //List<BModel> modelBList = new List<BModel>();
    ConcurrentBag<BModel> modelBList = new ConcurrentBag<BModel>();
    watch.Restart();
    //for(int i=0;i<200000;i++)
    //{
    //    modelBList.Add(new BModel
    //    {
    //        Id = modelAList[i].Id,
    //        Name = modelAList[i].Name,
    //        Author = modelAList[i].Author,
    //        Title = modelAList[i].Title,
    //        Topic = modelAList[i].Topic,
    //        ISBN = modelAList[i].ISBN
    //    });
    //}
    Parallel.ForEach(modelAList, x =>
    {
        modelBList.Add(new BModel
        {
            Id = x.Id,
            Name = x.Name,
            Author = x.Author,
            Title = x.Title,
            Topic = x.Topic,
            ISBN = x.ISBN
        });
    });
    watch.Stop();
    System.Diagnostics.Debug.WriteLine($"Convert :{modelBList.Count},milliseconds:{watch.ElapsedMilliseconds}");

}

Copy from https://stackoverflow.com/questions/57785475/source-array-was-not-long-enough-check-srcindex-and-length-and-the-arrays-low