c# - Optimize the performance of using HttpClient and TPL to validate proxies -

i'm trying use httpclient , tpl validate proxy addresses. i'm using simple , i've set servicepointmanager.defaultconnectionlimit = 100; before start.

the problem i've found result varies lot between consecutive runs. there can 4 valid proxies , run 1 second after give 194 valid proxies. i'm concerned maybe should handle task throttling. should myself here?

or there other issues should try handle?

internal class validator {     private readonly concurrentdictionary<string, long> _validatedproxydic = new concurrentdictionary<string, long>();     private async task<tuple<bool, long>> validateproxy(tuple<string, string, string> tuple)     {         try         {             string proxy = tuple.item1;             string url = tuple.item2;             string pattern = tuple.item3;              var handler = new httpclienthandler             {                 cookiecontainer = new cookiecontainer(),                 automaticdecompression = decompressionmethods.gzip | decompressionmethods.deflate,                 proxy = new webproxy(proxy, true),                 useproxy = true             };              var client = new httpclient(handler);             client.defaultrequestheaders.expectcontinue = false;             client.defaultrequestheaders.add("user-agent",                 "mozilla/5.0 (compatible; msie 10.0; windows nt 6.2; trident/6.0)");             client.defaultrequestheaders.add("connection", "keep-alive");             client.defaultrequestheaders.add("accept", "*/*");             client.timeout = timespan.frommilliseconds(10000);              var stopwatch = stopwatch.startnew();             var response = await client.getasync(url);             var str = await response.content.readasstringasync();              if (str.contains(pattern))                 _validatedproxydic.tryadd(proxy, stopwatch.elapsedmilliseconds);              return new tuple<bool, long>(str.contains(pattern), stopwatch.elapsedmilliseconds);         }         catch (exception ex)         {          }          return new tuple<bool, long>(false, -1);     }      public void foo(ienumerable<string> proxylist, string loginurl, string keyword)     {         var tasklist = new list<task<tuple<bool, long>>>();         foreach (var proxy in proxylist)         {             var tuple = new tuple<string, string, string>(proxy, loginurl, keyword);             var task = task.run(() => validateproxy(tuple));             tasklist.add(task);         }         var result = task.whenall(tasklist).result;          var validatedproxysortedlist = pair in _validatedproxydic orderby pair.value ascending select pair;          using (var sw = new streamwriter("proxyvalidatedlistsorted.txt"))         {             foreach (var proxy in validatedproxysortedlist)                 sw.writeline(proxy.key + "\t" + proxy.value);         }          console.writeline("found {0} proxies.", validatedproxysortedlist.count());     } }