annotations/Azaion.Common/Extensions/ParallelExt.cs

namespace Azaion.Annotator.Extensions;

public class ParallelOptions
{
    public int ProgressUpdateInterval { get; set; } = 100;
    public Func<int, Task> ProgressFn { get; set; } = null!;
    public double CpuUtilPercent { get; set; } = 100;
}

public class ParallelExt
{
    public static async Task ForEachAsync<T>(ICollection<T> source,
        Func<T, CancellationToken, ValueTask> processFn,
        ParallelOptions? parallelOptions = null,
        CancellationToken cancellationToken = default)
    {
        parallelOptions ??= new ParallelOptions
        {
            CpuUtilPercent = 100,
            ProgressUpdateInterval = 100,
            ProgressFn = i =>
            {
                Console.WriteLine($"Processed {i} item by Task {Task.CurrentId}%");
                return Task.CompletedTask;
            }
        };
        var threadsCount = (int)(Environment.ProcessorCount * parallelOptions.CpuUtilPercent / 100.0);

        var processedCount = 0;
        var chunkSize = Math.Max(1, (int)(source.Count / (decimal)threadsCount));
        var chunks = source.Chunk(chunkSize).ToList();
        if (chunks.Count > threadsCount)
        {
            chunks[^2] = chunks[^2].Concat(chunks.Last()).ToArray();
            chunks.RemoveAt(chunks.Count - 1);
        }
        var progressUpdateLock = new SemaphoreSlim(1);

        var tasks = new List<Task>();
        foreach (var chunk in chunks)
        {
            tasks.Add(await Task.Factory.StartNew(async () =>
            {
                foreach (var item in chunk)
                {
                    await processFn(item, cancellationToken);
                    Interlocked.Increment(ref processedCount);
                    if (processedCount % parallelOptions.ProgressUpdateInterval == 0 && parallelOptions.ProgressFn != null)
                        _ = Task.Run(async () =>
                        {
                            await progressUpdateLock.WaitAsync(cancellationToken);
                            try
                            {
                                await parallelOptions.ProgressFn(processedCount);
                            }
                            finally
                            {
                                progressUpdateLock.Release();
                            }
                        }, cancellationToken);
                }

            }, TaskCreationOptions.LongRunning));
        }
        await Task.WhenAll(tasks);
    }
}