Task.WaitAll()

sync-vs-async.cs

using RestSharp;
using System.Threading;

async Task<string> getResponse(string url)
{
    var start = DateTime.Now;

    var client = new RestClient();
    var request = new RestRequest(url);
    var response = await client.GetAsync<ResponseDto>(request);

    var end = DateTime.Now;

    return $"[{url}] {start} -> {end} : {response?.username}";
}

//////////////////////////////

Console.WriteLine($"[{DateTime.Now}] SYNCHRONOUS INVOCATIONS BEGIN");
var results = new List<string>();
for (int i = 0; i < 50; i++)
{
    var result = await getResponse("https://random-data-api.com/api/v2/users");
    results.Add(result);
}
Console.WriteLine($"[{DateTime.Now}] SYNCHRONOUS INVOCATIONS END");
foreach (var result in results)
{
    Console.WriteLine(result);
}

Console.WriteLine("\n");

//////////////////////////////

Console.WriteLine($"[{DateTime.Now}] ASYNCHRONOUS INVOCATIONS BEGIN");
var tasks = new List<Task<string>>();
for (int i = 0; i < 50; i++)
{
    var task = getResponse("https://random-data-api.com/api/v2/users");
    tasks.Add(task);
}
Task.WaitAll(tasks.ToArray());
Console.WriteLine($"[{DateTime.Now}] ASYNCHRONOUS INVOCATIONS END");
foreach (var task in tasks)
{
    Console.WriteLine(task.Result);
}

//////////////////////////////

class ResponseDto
{
    public int id { get; set; }
    public string uid { get; set; }
    public string password { get; set; }
    public string first_name { get; set; }
    public string last_name { get; set; }
    public string username { get; set; }
    public string email { get; set; }
}