1 using System;
 2 using System.Diagnostics;
 3 using System.Linq;
 4 using System.Net;
 5 using System.Net.Http;
 6 using System.Threading;
 7 using System.Threading.Tasks;
 8 
 9 namespace HttpClientTest
10 {
11     class Program
12     {
13         private const string _url = "http://localhost";
14         private static readonly Timer _timer = new Timer(TimerGet);
15         private static readonly HttpClient _timerClient = new HttpClient(new MyMessageHandler());
16         private static readonly HttpClient _workerClient = new HttpClient(new MyMessageHandler());
17 
18         static void Main(string[] args)
19         {
20             _timer.Change(5000, 5000); // Without this code, it works fine
21 
22             while (true)
23             {
24                 ParallelEnumerable.Range(0, 1000).WithDegreeOfParallelism(16).ForAll(i => WorkerGet());
25                 Console.WriteLine(DateTime.Now.ToString("mmssfff"));
26             }
27         }
28 
29         private static void TimerGet(object state = null)
30         {
31             var sw = Stopwatch.StartNew();
32             var response = _timerClient.GetAsync(_url).Result;
33             sw.Stop();
34 
35             Console.WriteLine("TimerGet:{0}ms", sw.ElapsedMilliseconds);
36         }
37 
38         private static void WorkerGet()
39         {
40             Thread.Sleep(1);
41 
42             var sw = Stopwatch.StartNew();
43             var response = _workerClient.GetAsync(_url).Result;
44             sw.Stop();
45 
46             if (sw.ElapsedMilliseconds > 200)
47             {
48                 Console.WriteLine("WorkerGet:{0}ms", sw.ElapsedMilliseconds);
49             }
50         }
51 
52         public class MyMessageHandler : HttpMessageHandler
53         {
54             protected async override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
55             {
56                 var response = new HttpResponseMessage(HttpStatusCode.OK) { Content = new StringContent("OK") };
57 
58                 var source = new TaskCompletionSource<HttpResponseMessage>();
59                 source.SetResult(response);
60                 return await source.Task;
61             }
62         }
63     }
64 }

 1 4102120
 2 4102628
 3 4103134
 4 WorkerGet:511ms
 5 WorkerGet:512ms
 6 TimerGet:511ms
 7 WorkerGet:510ms
 8 WorkerGet:510ms
 9 4104159
10 4104670
11 4105192
12 4105596
13 4106045
14 4106549
15 4107054
16 4107578
17 4108081
18 WorkerGet:510ms
19 TimerGet:510ms
20 WorkerGet:510ms
21 WorkerGet:510ms
22 WorkerGet:511ms
23 4109115
24 4109618
25 4110119
26 4110623
27 4111125
28 4111630
29 4112165
30 4112541
31 4112996
32 4113521
33 TimerGet:0ms
34 4114027
35 4114530
36 4115034
37 4115544