using System;

using System.Threading;

using System.Threading.Tasks;

using System.Collections.Concurrent;

using System.IO;

​

public class Program

{

    private static async Task UploadFile(FileInfo fileInfo, ImportFileInfo importFileInfo)

    {

        using (var proxy = new Proxy())

            using (var stream = new FileStream(fileInfo.FullName, FileMode.Open, FileAccess.Read))

            {

                importFileInfo.FileByteStream = stream;

                proxy.UploadAndImport(importFileInfo);

            }

​

        await Task.Run(() => Poller.Poll(timeoutSeconds: 90, intervalSeconds: 1, func: () =>

        {

            using (var proxy = new Proxy())

            {

                return proxy.UploadAndImportIsComplete(importFileInfo.OperationId);

            }

        }));

    }

}

​

public class Proxy : IDisposable

{

    static ImportFileInfo _inProgressRequest = null;

    static readonly ConcurrentDictionary<Guid, ImportFileInfo> WaitingRequests = new ConcurrentDictionary<Guid, ImportFileInfo>();

    public void UploadAndImport(ImportFileInfo request)

    {

        // Receive the incoming request

        WaitingRequests.TryAdd(request.OperationId, request);

        while (null != Interlocked.CompareExchange(ref _inProgressRequest, request, null))

        {

            // Wait for previous processing to complete

            Thread.Sleep(500);

        }

​

        // Process the incoming request

        ImportFile(request);

        Interlocked.Exchange(ref _inProgressRequest, null);

        WaitingRequests.TryRemove(request.OperationId, out _);

    }

​

    public bool UploadAndImportIsComplete(Guid operationId) => !WaitingRequests.ContainsKey(operationId);

    private void ImportFile(ImportFileInfo request)

    {

        // must run one at a time

    }

​

    public void Dispose()

    {

        // clean up stuff

    }

}

​

public class ImportFileInfo

{

    public Guid OperationId

    {

        get;

        set;

    }

​

    public Stream FileByteStream

    {

        get;

        set;

    }

}

​

public class Poller

{

    public static bool Poll(int timeoutSeconds, int intervalSeconds, Func<bool> func)

    {

        // do the polling...

        return true;

    }

}