What is the best way to make multiple requests to an API?

Question

I came to ask this question once again thinking that it would be beneficial for the community to have a canonical way of making several http requests to a particular API.

More specifically this question motivated me to ask my question.

What is the best way to make multiple requests to an API? (Take into account reducing as much time as possible to get all answers)

To be a little more concrete: How can I get the first 10 pages of the stackechange api, being https://api.stackexchange.com/2.2/answers?page=1&pagesize=10&order=desc&sort=activity&site=stackoverflow the front page.

Answer 1

Utilizing Tasks

The idea is to sign the orders and add them to a list of tasks with all requests. Then wait for the answers with Task.WaitAll:

var tasks = new Task<string>[10];
var api = "https://api.stackexchange.com/2.2/answers?page={0}&pagesize=10&site=stackoverflow";
using(var client = new HttpClient()){
    for(int i = 1 ; i < 11; ++i){
        var url = string.Format(api, i);
        tasks[i-1] = client.GetAsync(url)
            .ContinueWith(t => t.Result.Content.ReadAsStringAsync())
            .Unwrap();
    }

    Task.WaitAll(tasks);
    foreach (var resposta in tasks){
        Console.WriteLine(resposta.Result);
    }
}

In fact this other question questions this same approach.

An alternative (according to a quick measurement) more efficient than the one above and possibly more understandable can be obtained with the use of keyword await:

var tasks = new List<Task<HttpResponseMessage>>();
using (var client = new HttpClient())
{
    for (int i = 1; i < paginas; ++i)
    {
        var url = string.Format(api, i);
        tasks.Add(client.GetAsync(url));
    }

    var respostas = await Task.WhenAll(tasks);
    var todas = new List<string>();
    foreach(var resposta in respostas)
    {
        todas.Add(await resposta.Content.ReadAsStringAsync());
    }
    return todas;
}

But never make the following code:

var respostas = new List<string>();
using (var client = new HttpClient())
{
    for (int i = 1; i < paginas; ++i)
    {
        var url = string.Format(api, i);
        var resposta = await client.GetAsync(url);
        respostas.Add(await resposta.Content.ReadAsStringAsync());
    }
}
return respostas;

With this code requests are not being made in parallel and take longer so.