C# WinSCP .NET assembly: How to upload multiple files asynchronously

Question

I am using WinSCP .NET assembly for uploading files. I want to upload multiple files asynchronous way. I have created a method but it works as single upload.

public class UploadingData {

    private SessionOptions _sessionOptions;
    private Session _session;

    //connection etc

    private void OnConnected() {

        foreach (var fileInfo in localFilesList)
        {
            var task = Task.Factory.StartNew(() => UploadFilesAsync(fileInfo));
        }
    }

    private async Task UploadFilesAsync(string file) {

        string remoteFilePath = _session.TranslateLocalPathToRemote(file, @"/", "/test_data_upload");
        var uploading = _session.PutFiles(file, remoteFilePath, false);

        //When Done

        await Task.Run(() => Thread.Sleep(1000));
    }
}

Please suggest me correct way. Thanks

Answer 1

The API of the Session class can be used from a single thread only. If you use it from multiple threads, it will block.

So if you need parallel transfers, you have to create a separate Session instance for each thread.

private async Task UploadFilesAsync(string file)
{
    using (Session session = new Session())
    {
        session.Open(_sessionOptions);
        string remoteFilePath =
            RemotePath.TranslateLocalPathToRemote(file, @"/", "/test_data_upload");
        session.PutFiles(file, remoteFilePath, false).Check();
    }

    ...
}

See also WinSCP article Automating transfers in parallel connections over SFTP/FTP protocol with code examples for C# and PowerShell.

Note that you should not use more than few sessions/threads (about 4). With more sessions, you will hardly get better throughput.

Answer 2

You can use BackgroundWorker class like this:

        string[] images = new string[50];
        foreach (var path in images)
        {
            BackgroundWorker w = new BackgroundWorker();
            //50 independently async Threads
            w.DoWork += delegate (object s, DoWorkEventArgs args) 
            {
                Upload(args.Argument.ToString());
            };
            w.RunWorkerAsync(path);
        }