Task based version #1

namespace WordFrequencyFinder
{
    class Program
    {
        static async Task Main(string[] args)
        {
            if (args.Length < 2)
            {
                Console.WriteLine("Usage: WordFrequencyFinder <directory path> <min word length>");
                return;
            }

            string directoryPath = args[0];
            if (!int.TryParse(args[1], out int minWordLength))
            {
                Console.WriteLine("Invalid minimum word length.");
                return;
            }

            if (!Directory.Exists(directoryPath))
            {
                Console.WriteLine("Directory does not exist.");
                return;
            }

            var wordFrequency = await GetWordFrequenciesAsync(directoryPath, minWordLength);
            var topWords = wordFrequency.OrderByDescending(kvp => kvp.Value).Take(10);

            Console.WriteLine("Top-10 most used words:");
            foreach (var word in topWords)
            {
                Console.WriteLine($"{word.Key}: {word.Value}");
            }
        }

        static async Task<ConcurrentDictionary<string, int>> GetWordFrequenciesAsync(string directoryPath, int minWordLength)
        {
            var wordFrequency = new ConcurrentDictionary<string, int>();
            var files = Directory.GetFiles(directoryPath, "*.txt");

            var tasks = files.Select(file => ProcessFileAsync(file, minWordLength, wordFrequency)).ToArray();
            await Task.WhenAll(tasks);

            return wordFrequency;
        }

        static async Task ProcessFileAsync(string filePath, int minWordLength, ConcurrentDictionary<string, int> wordFrequency)
        {
            var content = await File.ReadAllTextAsync(filePath);
            var words = Regex.Split(content.ToLowerInvariant(), @"\W+")
                             .Where(word => word.Length >= minWordLength);

            foreach (var word in words)
            {
                wordFrequency.AddOrUpdate(word, 1, (key, oldValue) => oldValue + 1);
            }
        }
    }
}