C# Winforms Cross Thread event extremely slow posting to HTTPClient - multithreading

Question

The following code is a serial port event inside a winforms form ( so obviously running on it's own thread ). The slow line of code is run elsewhere ( in Nodejs ) and takes about 10 seconds. In this code the same line takes 45 seconds - sometimes 60 seconds.
private async void SerialPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
SerialPort sp = (SerialPort)sender;
string indata = sp.ReadLine().Replace("?","").Replace(" ","");
if(indata != null)
{
var weightMatch = Regex.Match(indata, #"(\d+\.\d+)kg$");
var weight = weightMatch.Groups[1].Value;
var message = barcode + " Weight:" + weight;
this.Invoke(new Action(() => { scanData.Add(new ScanDataItem(scanData.Count + 1, message, "")); }));
this.Invoke(new Action(() => { mainList.SelectedIndex = mainList.Items.Count - 1; }));
string jsonData = "";
// ***************************************************************
// The following line is about 30 seconds slower than it should be - inner function calls a web service
// ***************************************************************
var jsonString = await TrayWeighScan.doOrder(barcode, Decimal.Parse(weight));
try
{
var jsonDoc = JsonDocument.Parse(jsonString);
jsonData = JsonSerializer.Serialize(jsonDoc, new JsonSerializerOptions { WriteIndented = true });
}
catch (Exception)
{
jsonData = jsonString;
}
this.Invoke(new Action(() => { scanData.Last().responseData = jsonData; }));
this.Invoke(new Action(() => { responseTextBox.Text = jsonData; }));
this.Invoke(new Action(() => { statusTextBox.Text = "Ready to Scan"; }));
this.Invoke(new Action(() => { busy = false; }));
}
}
public class TrayWeighScan
{
//private static readonly HttpClient httpClient = new();
public static async Task<string> doOrder(string orderNumber, decimal weight )
{
HttpClient httpClient = new();
var url = "http://r2hserver/logistics/weighscan?orderNumber="+orderNumber+"&weight="+weight.ToString("F2");
HttpResponseMessage response = await httpClient.GetAsync(url);
string responseText = await response.Content.ReadAsStringAsync();
return responseText;
}
}
If I run the "slow" line directly from a form button, 11 seconds.
private async void btnUrlTest_Click(object sender, EventArgs e)
{
string orderNumber = "ORD100302338";
decimal weight = 1.606m;
//following line - 11 seconds.
var a = await TrayWeighScan.doOrder(orderNumber,weight);
var b = "";
}

Answer 1

Hans Passant as pointed out that most likely the cause isn't in the code structure at all, and most likely he's right. To test the hypothesis, descend into trayWeighScan.doOrder and change the async HttpClient async call into a sync call. If the problem goes away, my answer is good. If the problem remains, look elsewhere, say the network or the client machine's TCP stack or AV or somesuch.
I've not seen this exact thing before, but I've learned that launching async operations in a WinForms app doesn't do the expected when launched in the naive way. The following should work much better
Task.Run(async () => {
var jsonString = await trayWeighScan.doOrder(barcode, Decimal.Parse(weight);
try
{
var jsonDoc = JsonDocument.Parse(jsonString);
jsonData = JsonSerializer.Serialize(jsonDoc, new JsonSerializerOptions { WriteIndented = true });
}
catch (Exception)
{
jsonData = jsonString;
}
this.Invoke(new Action(() => { scanData.Last().responseData = jsonData; }));
this.Invoke(new Action(() => { responseTextBox.Text = jsonData; }));
this.Invoke(new Action(() => { statusTextBox.Text = "Ready to Scan"; }));
this.Invoke(new Action(() => { busy = false; }));
});
Wrapping winforms-originating async in Task.Run seems to completely fix the problem.
A lot of stuff talks about .ConfigureAwait() being the solution; but it's overly complex. The simplest and best solution is to only spawn async/await from threadpool threads, which means starting an async/await chain from Task.Run.