HttpClient - Send a batch of requests

Question

I want to iterate a batch of requests, sending each one of them to an external API using HttpClient class.

  foreach (var MyRequest in RequestsBatch)
  {
            


        

Answer 1

I agree with the accepted answer in that the key to speeding things up is to run the requests in parallel. But any solution that forces additional threads into the mix by use of Task.Run or Parallel.ForEach is not gaining you any efficiency with I/O bound asynchronous operations. If anything it's hurting.

You can easily get all calls running concurrently while letting the underlying async subsystems decide how many threads are required to complete the tasks as efficiently as possible. Chances are that number is much smaller than the number of concurrent calls, because they don't require any thread at all while they're awaiting a response.

Further, the accepted answer creates a new instance of HttpClient for each call. Don't do that either - bad things can happen.

Here's a modified version of the accepted answer:

var httpClient = new HttpClient {
    Timeout = TimeSpan.FromMilliseconds(5)
};

var taskList = new List<Task<JObject>>();

foreach (var myRequest in RequestsBatch)
{
    // by virtue of not awaiting each call, you've already acheived parallelism
    taskList.Add(GetResponseAsync(endPoint, myRequest));
}

try
{
    // asynchronously wait until all tasks are complete
    await Task.WhenAll(taskList.ToArray());
}
catch (Exception ex)
{
}

async Task<JObject> GetResponseAsync(string endPoint, string myRequest)
{
    // no Task.Run here!
    var response = await httpClient.PostAsJsonAsync<string>(
        string.Format("{0}api/GetResponse", endpoint), 
        myRequest);
    return await response.Content.ReadAsAsync<JObject>();
}

Answer 2

It doesn't look like you're actually running a seperate thread for each request. Try something like this:

var taskList = new List<Task<JObject>>();

foreach (var myRequest in RequestsBatch)
{
    taskList.Add(GetResponse(endPoint, myRequest));
}

try
{
    Task.WaitAll(taskList.ToArray());
}
catch (Exception ex)
{
}

public Task<JObject> GetResponse(string endPoint, string myRequest)
{
    return Task.Run(() =>
        {
            HttpClient httpClient = new HttpClient();

            HttpResponseMessage response = httpClient.PostAsJsonAsync<string>(
                 string.Format("{0}api/GetResponse", endpoint), 
                 myRequest, 
                 new CancellationTokenSource(TimeSpan.FromMilliseconds(5)).Token);

            JObject resultResponse = response.Content.ReadAsAsync<JObject>();
        });
}