25 concurrent async WCF calls to orchestrate using Tasks - wcf

Question

I have an application (.NET 4.0) that loads administrative data on startup. I have to make 25 concurrent async WCF calls, some of them are quick (40ms), some others take longer to execute, up to 882 ms. I plan to store the data locally, but for the very first application startup, it needs to be done quickly as possible.
It should be noted that the proxies are in a library targetting .NET 3.5 and are internally using BeginXxx and EndXxx methods pattern wrapped into an async method whith the help of Jeffrey Richter's Async Enumerator.
The WCF channel factories for each client proxy that will be used are opened before launching the calls.
At this time, I'm using Task.Factory.StartNew with an action that launch each async call. The experience is the following :
All BeginXXX calls are all sent.
The program seems to work outside of my code for at least 10 seconds.
Finally all the EndXXX calls are sent to retreive the results.
I'm wondering why such a delay occurs. My computer has 4 core, If the number of concurrent calls are limited to 4, there is no delay at all, as soon as I add another call, a delay is experienced.
Any help appreciated.
EDIT 1 : The binding used is netTcpBinding.
Server configuration is following :
<netTcpBinding>
<binding transactionFlow="true" listenBacklog="500" maxReceivedMessageSize="400000"
portSharingEnabled="false">
<readerQuotas maxDepth="200" />
<reliableSession enabled="false" />
<security mode="None">
<transport clientCredentialType="None" protectionLevel="None" />
<message clientCredentialType="None" />
</security>
</binding>
</netTcpBinding>
<service name="AdminService">
<endpoint address="" binding="netTcpBinding" bindingConfiguration=""
contract="IAdmin">
<identity>
<dns value="localhost" />
</identity>
</endpoint>
<endpoint address="mex" binding="mexTcpBinding" bindingConfiguration=""
contract="IMetadataExchange" />
</service>
EDIT 2: Following are the default throttling values set by the WCF 4.5 runtime on a 4 Core machine.
ListenBacklog is [500]
MaxConnections is [48]
MaxConcurrentCalls is [64]
MaxConcurrentInstances is [2147483647]
MaxConcurrentSessions is [400]
EDIT 3 : Here is the code using J.Richter's AsyncEnumerator :
private IEnumerator<int> DoWorkGetXXXX(AsyncEnumerator<MyResult> ae)
{
ae.ThrowOnMissingDiscardGroup(true);
IClientChannel proxy = (IClientChannel)CreateChannel(_bindingName);
bool success = false;
try
{
proxy.Open();
// The call to BeginXXX goes here
((IAcaccount)proxy).BeginGetXXX(..., ae.EndVoid(0, DiscardGetXXX), proxy);
//
yield return 1;
if (ae.IsCanceled())
{
goto Complete;
}
// Iterator was not canceled, process should continue.
// The call to EndXXX goes here
IAsyncResult ar = ae.DequeueAsyncResult();
try
{
ae.Result = ((IAcaccount)ar.AsyncState).EndGetXXX(ar);
proxy.Close();
success = true;
}
// In the mean time, we catch and rethrow :)
// If this exception occurs, we should retry a call to the service
catch (FaultException<AppFabricCachingException> retry)
{
}
// fatal Exception in data service, administrator action required...
catch (FaultException<EFExecutionException> fatal)
{
}
catch (FaultException<EFUpdateException> fatal)
{
}
catch (FaultException<EFNoRowException> nr)
{
}
catch (FaultException fe)
{
}
catch (ServiceActivationException sae)
{
}
catch (CommunicationException ce)
{
}
//
}
finally
{
// If an error occurred, abort the proxy.
if (!success)
{
proxy.Abort();
}
}
// End of operations.
Complete:
proxy = null;
}

Answer 1

You could try to play with the value of serviceThrottling, as well as maxItemsInObjectGraph, maxBufferSize, MaxBufferPoolSize (i have them set to int.MaxValue).