c# - Multiple simultaneous requests to the same http host -

i have c# desktop application, needs make multiple simultaneous http requests same web server. here's test performed check whether requests happen simultaneously:

1. on web server, created test page sleeps 3 seconds (simulates long-running task), returns current date/time. here's code (vb.net):

   <%system.threading.thread.sleep(3000)%><%=now%>

2. in c# app, have function makerequest() uses system.net.http.httpclient make web request, , returns response string.

3. then in c# app there's function invoked button click, calls makerequest() multiple times asynchronously:

   var responses = await task.whenall(makerequest(), makerequest(), makerequest());

in above example, makerequest() called 3 times. see on web server when monitor requests/sec performance counter, gets 2 requests, , 3 sec later 1 more request. that's design, because default value system.net.servicepointmanager.defaultconnectionlimit 2, c# app can send 2 requests @ time, though asked 3. overall time c# app took complete button click 6 sec.

now in c# app, set servicepointmanager.defaultconnectionlimit = 1000000. time requests/sec on web server shows 3, , button click in c# app completes in 3 seconds. far.

next change c# app make 60 simultaneous calls rather 3. that's things interesting. when click button, expect see requests/sec on web server spike 60, , c# app complete button click in 3 sec. instead web server requests/sec showing 5, after 3 seconds 5 more, etc., until 60 requests have been made. when click button again, same picture except requests/sec spike 10 or 15, , button click completes faster. click again - time requests/sec show 2 spikes 30, , button click completes in 6 sec. subsequent button clicks result in requests/sec spiking first 40 20 (for total of 60 requests), 50 , 10, maybe 55 , 5, , c# app starts sending 60 requests in 1 go. button click completes in 3 sec, , requests/sec on web server shows 1 spike 60. if continue pushing button, consistently 60 requests being made simultaneously.

but that's not all. if stop pushing button, c# app seems "forget" it's previous achievement. not restart app, stop pushing button minute, , on next push go 5 requests @ time, , above scenario repeat if keep pushing button continuously.

i performed above test mvc - copied , pasted code c# app mvc page. got same result.

can please explain what's going on? thank you

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here's code of c# app. it's winforms app, , code lives inside form class:

<!-- language: lang-c# --> private httpclient _httpclient = new httpclient();  private async void button1_click(object sender, eventargs e) {     servicepointmanager.defaultconnectionlimit = 1000000;      var sw = stopwatch.startnew();     var responses = await task.whenall(makerequest(), makerequest(), makerequest());     sw.stop();      var msg = string.join("\r\n", responses) + "\r\n\r\ntime elapsed: " + sw.elapsedmilliseconds;     messagebox.show(msg); }  private async task<string> makerequest() {     using (var message = await _httpclient.getasync("http://testserver/testpage.aspx"))     {         return await message.content.readasstringasync();     } } 

two reasons:

1. client windows skus limit number of concurrent iis requests 10.
2. apparently, client uses synchronous io or otherwise blocking. takes while thread pool warmed up. threads injected on time. either use async io , non-blocking or make sure threads need there. regarding "forgetting": idle pool threads retired on time. tests therefore timing sensitive. unreliable, don't put production.