HttpClient GetAsync ThreadPool Starvation

Question

We have a microservice-oriented internal stack. All microservices are built on top Nancyand registered as windows services using topshelf.

One of the services that handles most of the traffic (~ 5000 req / s) started to have a hunger problem in threadpool on 3 out of 8 servers.

This is the exception that we get when we reach a specific endpoint:

System.InvalidOperationException: There were not enough free threads in the ThreadPool to complete the operation.
   at System.Net.HttpWebRequest.BeginGetResponse(AsyncCallback callback, Object state)
   at System.Net.Http.HttpClientHandler.StartGettingResponse(RequestState state)
   at System.Net.Http.HttpClientHandler.StartRequest(Object obj)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at RandomNamedClient.<GetProductBySkuAsync>d__20.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at ProductService.<GetBySkuAsync>d__3.MoveNext() in ...\ProductService.cs:line 34
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at ProductModule.<>c__DisplayClass15.<<.ctor>b__b>d__1d.MoveNext() in ...\ProductModule.cs:line 32

This endpoint calls another service that is outside my team domain to receive product data. Its implementation is as follows:

Get["/product/sku/{sku}", true] = async (parameters, ctx) =>
{
    string sku = parameters.sku;
    var product = await productService.GetBySkuAsync(sku);
    return Response.AsJson(new ProductRepresentation(product));
};

ProductService.GetBySkuAsync(string sku) implementation:

public async Task<Product> GetBySkuAsync(string sku)
{
    var productDto = await randomNamedClient.GetProductBySkuAsync(sku);
    if (productDto == null)
    {
        throw new ProductDtoNotFoundException("sku", sku);
    }

    var variantDto = productDto.VariantList.FirstOrDefault(v => v.Sku == sku);

    if (variantDto == null)
    {
        throw new ProductVariantDtoNotFoundException("sku", sku);
    }

    return MapVariantDtoToProduct(variantDto, productDto);
}

RandomNamedClient.GetProductBySkuAsync(string sku) implementation (from internal package):

public async Task<ProductDto> GetProductBySkuAsync(string sku)
{
  HttpResponseMessage result = await this._serviceClient.GetAsync("Product?Sku=" + sku);
  return result == null || result.StatusCode != HttpStatusCode.OK ? (ProductDto) null : this.Decompress<ProductDto>(result);
}

RandomNamedClient.Decompress<T>(HttpResponseMessage response) implementation:

private T Decompress<T>(HttpResponseMessage response)
{
  if (!response.Content.Headers.ContentEncoding.Contains("gzip"))
    return HttpContentExtensions.ReadAsAsync<T>(response.Content).Result;
  using (GZipStream gzipStream = new GZipStream((Stream) new MemoryStream(response.Content.ReadAsByteArrayAsync().Result), CompressionMode.Decompress))
  {
    byte[] buffer = new byte[8192];
    using (MemoryStream memoryStream = new MemoryStream())
    {
      int count;
      do
      {
        count = gzipStream.Read(buffer, 0, 8192);
        if (count > 0)
          memoryStream.Write(buffer, 0, count);
      }
      while (count > 0);
      return JsonConvert.DeserializeObject<T>(Encoding.UTF8.GetString(memoryStream.ToArray()));
    }
  }
}

All our services are built as Release / 32-bit. We did not configure anything to use threadpool.

Answer 1

, , - Decompress<T>, async Task.Result. , threadpool, , , ( shouldn 't ). , , , NancyFX ( ), .

, - async, API, . , , ConfigureAwait(false) .

( - , Stream.CopyToAsync())

async :

private async Task<T> DecompressAsync<T>(HttpResponseMessage response)
{
    if (!response.Content.Headers.ContentEncoding.Contains("gzip"))
        return await response.Content.ReadAsAsync<T>();

    const int bufferSize = 8192;        
    using (GZipStream gzipStream = new GZipStream(
                                   new MemoryStream(
                                        await response.Content.ReadAsByteArrayAsync()), 
                                        CompressionMode.Decompress))
    using (MemoryStream memoryStream = new MemoryStream())
    {
        await gzipStream.CopyToAsync(memoryStream, bufferSize);
        return JsonConvert.DeserializeObject<T>(
                    Encoding.UTF8.GetString(memoryStream.ToArray()));
    }
}