Simulate Concurrent WCF Client Calls And Measure Response Time

I am trying to simulate X number of concurrent requests for a WCF Service and measure the response time for each request. I want to have all the requests hit the Service a开发者_如何学JAVAt more or less the same time.

As the first step I spawned X number of Threads, using the Thread class, and have invoked the Start method. To synchronize all the requests, on the Thread callback I open the connection and have a Monitor.Wait to hold the request from being fired, till all the Threads are created and started. Once all the Threads are started, I call Monitor.PulseAll to trigger the method invocation on the WCF Client Proxy.

When I execute the requests this way, I see a huge delay in the response. A request that should just a few milliseconds, is taking about a second.

I also noticed huge lag between the time the request is dispatched and the time it was received at the service method. I measured this by send sending client time stamp as a parameter value to the service method for each request.

I have the following settings. Assume "X" to the Concurrent number of requests I want to fire. Also note with the following settings I don't get any Denial of Service issues.

1. The Call chain is as follows,Client->Service1->Service2->Service3
2. All Services are PerCall with Concurrency set to Multiple.
3. Throttling set to X Concurrent calls, X Concurrent Instances.
4. MaxConnections, ListenBacklog on the Service to X.
5. Min/Max Threads of ThreadPool set to X on both Client and Server (I have applied the patch provided by Microsoft).

Am not sure if the response time I'm measuring is accurate. Am I missing something very trivial?

Any inputs on this would be of great help.

Thanks.

-Krishnan

I did find the answer by myself the hard way. All this while, the way I was measuring the response time was wrong. One should spawn X number of threads, where X is the number of concurrent users one wants to simulate. In each thread, open the connection only once and have while loop to only execute the WCF Method that you want to test for a given duration. Measure the response time against each return, accumulate it and average it out against the number of calls that were executed within the given duration.

If all your outgoing calls are coming from a single process, it is likely that the runtime is either consolidating multiple requests onto a single open channel or capping the number of concurrent requests to a single target service. You may have better results if you move each simulated client into its own process, use a named EventWaitHandle to synchronize them, and call #Set() to unleash them all at once.

There is also a limit to the number of simultaneous pending (TCP SYN or SYN/ACK state) outgoing TCP connections allowed by desktop builds of Windows; if you encounter this limit you will get event 4226 logged and the additional simultaneous connections will be deferred.