Delphi SOAP Client can not keep more than 2 concurrent requests. How to increase?

Question

I have a multi-user COM+ application that needs to make multiple requests on SOAP WebServices. Each SOAP request may last from 10 to 60 seconds (that is not under my control). Problem is, I can never make more than 2 requests at the same time.

When I have, for example, 3 concurrent requests the third requests only starts when the second one finishes. I watched the same behaviour on a console application (for testing purposes) making multiple concurrent requests to the same WebService, and I was again limited to 2 requests.

When I tried to consume the same WebServices with another language (C#) the same happened, BUT, on the C# client there is a property that solves the problem:

System.Net.ServicePointManager.DefaultConnectionLimit 

When I increased that property I could keep whatever number of concurrent requests I wanted. Is there a property similar to that one on Delphi?

I'm using the WSDL importer tool to consume the Web Services (Delphi XE2).

Answer 1

Delphi uses Wininet.dll to make its SOAP requests, IE uses the same DLL. This limitation is in fact documented.

You have 2 choices:

• adapt the registry like stated in the KB article
• Use InternetSetOption before the SOAP call:

small code sample (please note that it does not include error checking):

Const 
  INTERNET_OPTION_MAX_CONNS_PER_SERVER = 73; 
  INTERNET_OPTION_MAX_CONNS_PER_1_0_SERVER = 74; 
var 
  MaxConnections : Integer;

begin 
  MaxConnections := 10; // adapt to your needs
  InternetSetOption(Nil, INTERNET_OPTION_MAX_CONNS_PER_SERVER, @MaxConnections , SizeOf(MaxConnections )); 
  InternetSetOption(Nil, INTERNET_OPTION_MAX_CONNS_PER_1_0_SERVER, @MaxConnections , SizeOf(MaxConnections )); 
 // do SOAP call
end;

Answer 2

By default, Delphi SOAP programs uses WinInet in Windows, and Indy (TIdHTTP) in other platforms (see USE_INDY directive in SOAPHTTPTrans.pas unit), to comunicate with the server. [1]

You can try using Indy on Windows by defining USE_INDY and recompile the SOAP library (however I have not done this myself so the detailed steps to do this are unknown to me).

p.s. the linked article also indicates that UseNagle should be set to False.