CustomLogger.cs

public class CustomLog : IDisposable, IAsyncDisposable
{
	StreamWriter _log;
	Channel<string> _channel = Channel.CreateUnbounded<string>();
	Task _writer;
	CancellationTokenSource _cancellationTokenSource = new CancellationTokenSource();
	Timer _flusher;
	SemaphoreSlim _semaphore = new SemaphoreSlim(1, 1);

	public CustomLog(string logName)
	{
		var path = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "Todo");
		Directory.CreateDirectory(path);
		var file = Path.Combine(path, logName + ".log");
		try
		{
			_log = new StreamWriter(file, true);
		}
		catch
		{
			file = Path.Combine(path, logName + Guid.NewGuid().ToString("N") + ".log");
			_log = new StreamWriter(file, true);
		}
		_writer = WriterWorker(_cancellationTokenSource.Token);
		_flusher = new Timer(async _ =>
		{
			await _semaphore.WaitAsync();
			try
			{
				await _log.FlushAsync();
			}
			finally
			{
				_semaphore.Release();
			}
		}, null, TimeSpan.Zero, TimeSpan.FromSeconds(5));
	}

	async Task WriterWorker(CancellationToken cancellationToken)
	{
		await foreach (var line in _channel.Reader.ReadAllAsync(cancellationToken))
		{
			await _semaphore.WaitAsync();
			try
			{
				await _log.WriteLineAsync(line);
			}
			finally
			{
				_semaphore.Release();
			}
		}
	}

	public void Log(string line)
	{
		_channel.Writer.TryWrite(line);
	}

	public void Dispose()
	{
		_cancellationTokenSource.Cancel();
		_writer.Wait();
	}

	public async ValueTask DisposeAsync()
	{
		_cancellationTokenSource.Cancel();
		await _writer;
	}
}