it seems that service method are not really called asynchronously - silverlight

Question

Regarding my previous post: 910220 - service methods run dependently
since the code and what I meant about the problem I had with it was a bit complex, I come again with a completely changed code which explains itself better.
In client side, we have:
#define USE_ONLY_ONE_INSTANCE
using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using CountTester.ServiceReference1;
namespace CountTester
{
public partial class MainPage : UserControl
{
#if USE_ONLY_ONE_INSTANCE
private readonly Service1Client _sc = new Service1Client();
#endif
public MainPage()
{
InitializeComponent();
#if USE_ONLY_ONE_INSTANCE
_sc.CountCompleted += OnCountCompleted;
#endif
}
void OnCountCompleted(object sender, AsyncCompletedEventArgs e)
{
if (e.Error != null)
throw new Exception(string.Format("Count Error {0}", e.Error));
}
private void UserControl_Loaded(object sender, RoutedEventArgs e)
{
for (int i = 0; i < 100; i++)
{
#if USE_ONLY_ONE_INSTANCE
_sc.CountAsync(i);
#else
var sc = new Service1Client();
sc.CountCompleted += OnCountCompleted;
sc.CountAsync(i);
//sc.CloseAsync();
#endif
}
}
}
}
this is code behind of the XAML. In the code I call a service method 100 times. I tried both cases and get exception in both cases:
case 1: I use only one instance of the proxy for all communications with server.
case 2: I use an instance for each communication with server.
Let's see the code at server before more description:
using System.IO;
using System.ServiceModel;
using System.ServiceModel.Activation;
using System.Text;
using System.Threading;
namespace CountTester.Web
{
[ServiceContract(Namespace = "")]
[SilverlightFaultBehavior]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class Service1
{
const string logFileName = #"h:\CountTester.log";
object _logLock = new object();
void log(string s)
{
lock (_logLock)
{
var streamWriter = new StreamWriter(logFileName, true, Encoding.ASCII);
streamWriter.Write(s);
streamWriter.Close();
}
}
Service1()
{
//File.Delete(logFileName);
}
[OperationContract]
public void Count(int counter)
{
log(string.Format("{0}\n", counter));
Thread.Sleep(3000);
}
}
}
Count is the service method which is called. I deliberately wait 3 seconds in the method. what I expect is that the for at the client get accomplished with no delay. I expect the method gets called asynchronously and this means that first call doesn't affect on the second call.
In another words, if i call the method and it waits to get accomplished, calling it again doesn't get delayed.
While this is the case. how can I figure out that this happens? by using Tail for Windows, I find that the number which is logged is delayed in getting logged. I also figure out this when I see that I get time out exception in response to calling the service method (Count Error...). I hope I could clarify my question.
I also wonder when I see malfunctioning of the program (Exception), when I uncomment the line in which I've closed the service?
Please answer these two questions.

Answer 1

Question 1:
By default your IIS web service will only allow 2 simultaneous requests from the same IP address. This limitation is a default to stop DOS (Denial Of Service) attacks.
That means the subsequent 98 calls are waiting at least 3 seconds, per pair, while the previous ones complete. Eventually you will hit the default 30 second(?) server timeout long before the last requests are processed.
If you insist on running that many simultaneous requests (you shouldn't anyway), you will need to increase the default limits in your web.config file on the server. See my other answer here for more details
Question 2:
You should not close an async call immediately after starting it... the call is still in progress. That code makes no sense.
Notes:
Logging is delayed anyway, for efficiency, so don't use that as a guide.