Delphi Soap WebServer doesn't allow more than 2 calls at a time

Question

I have a problem with a SOAP WebServer: if I have a method on the server that takes a few seconds to give a result, and I can't make more than two calls "simoultaneously" (called from threads) from my client application (developed in Delphi Also - just for testing, the final client app will be web based). I mean that the threads are somehow serialized, and I don't know if it is supposed to happen like this or if I am doing something wrong, or if I need to make a certain setting.

Delphi XE2 Professional, Windows 7 64-bit

Link to my zipped project: http://1drv.ms/Nwu9nY

Server Method:

function TServiciu.Test: string;
var t0, t1, Duration : Cardinal;
    Guid : tguid;
    RGuid : HRESULT;
    received : boolean;
const MaxTime : Cardinal = 3000;
begin
  Result := '';
  RGuid := CreateGuid(Guid);
  if RGuid = S_OK then
    Result := GuidToString(Guid);
  t0 := GetTickCount;
  t1 := GetTickCount;
  duration := t1 - t0;
  while (Duration < Maxtime) do begin
    //waiting for something to be written in a db by another program
    //I am doing querys to the database for that result
    if received then begin
      Result := Result + '_RECEIVED_' + DateTimeToStr(Now);
      Break;
    end;
    t1 := GetTickCount;
    duration := t1 - t0;
    if duration > Maxtime then begin //MaxTime allowed is exceded
      Result := Result + '_NOTRECEIVED_' + DateTimeToStr(Now);
      Break;
    end;
  end;
end;

Client Procedure Execute of my thread:

procedure TThreadTest.Execute;
begin
  try
    // OleCheck will raise an error if the call fails
    OleCheck(CoInitializeEx(NIL, COINIT_MULTITHREADED or COINIT_SPEED_OVER_MEMORY));
    try
      s := 'Calling Method Test; Result=' +
      Self.ThGetService.Test;
      Synchronize(self.ScrieRezultat); //write result in memo
    finally
      CoUninitialize;
      FreeAndNil(self.ThHttprio);
    end;
  except
    // We failed, do something
  end;
end;

Answer 1

Hello I solved my problem, the thing was quite foolish, I had my server set up as HTTP 1.1. Connections to a single HTTP 1.1 server are limited to two simultaneous connections. http://support2.microsoft.com/kb/183110

Answer 2

I am able to handle 40 concurrent calls with no trouble (actually more than that), but I'm using a different approach. My service is a CGI executable, so IIS manages the connections. When a SOAP request is made, IIS spins up a new instance of myapp_cgi.exe to handle the request. I top out at 40 TPS, but I am load-balanced across 4 servers so I can actually do 160 TPS, sustainable all day long, if necessary.

Answer 3

I just had a very similar problem and I'm pretty sure your problem is on your client, not on your server. See this topic here.