HPC Pack SOA Tutorial II – Batch mode

In the last blog post, we implemented a simple SOA client and service. However in most cases, the HPC algorithm is not as simple as adding two numbers. Some services are more complex and run for hours. For such services, the end user normally submits all the requests, then retrieves the responses in a couple of hours. This represents a challenge for the developers. For example, can we close the client application after sending all the requests, and then start another client to get the responses the next day? This blog post is to guide you to design the application to handle such scenarios.

The key requirement of the batch mode is to make sure the requests won’t be lost after being successfully sent, and the result generated by the service won’t be lost either.

Let’s create a new service to explain how to create such reliable computations. We create a service which can do prime factorization. Then, we will write a client application to submit 100 big numbers to the service, and then start another client application to retrieve the results.

Implement the service

Download the accompanying code sample to build the service.

It’s as simple as the first example.

Here is the service contract:

[ServiceContract]    publicinterfaceIPrimeFactorization    {         [OperationContract]         List<int> Factorize(intn);    }

Here is the service implementation:

public List<int>Factorize(int n)     {         List<int> factors = newList<int>();         for (inti = 2; n > 1; )         {             if(n % i == 0)             {                 factors.Add(i);                 n /= i;             }             else             {                 i++;             }         }         returnfactors;     }

 

Implement the client to send requests

HPC Pack provides a feature called DurableSession. It makes sure all the requests and the responses are persisted.

Let’s write a client application to send the requests.

a. First we need to prepare the session info. This is the same as in the previous tutorial.

SessionStartInfo info = new SessionStartInfo("head.contoso.com", "PrimeFactorizationService");

b. Now we need to create a DurableSession object, like the following code.

//Create a durable session DurableSession session = DurableSession.CreateSession(info); Console.WriteLine("Session {0} has been created", session.Id);

 

c. Create a BrokerClient object to send requests.

//Send batch request     Random random = newRandom();     constintnumRequests = 100;     using (BrokerClient<IPrimeFactorization>client = newBrokerClient<IPrimeFactorization>(session))     {         Console.WriteLine("Sending {0} requests...", numRequests);         for (inti = 0; i < numRequests; i++)         {             int number = random.Next(1, Int32.MaxValue);             FactorizeRequest request = newFactorizeRequest(number);             //The second param is used to identify each request.             //It can be retrieved from the response.             client.SendRequest<FactorizeRequest>(request, number);         }         client.EndRequests();         Console.WriteLine("All the {0} requests have been sent", numRequests);     }

Here we call EndRequests() to indicate that we have submitted all the requests. After calling EndRequests() you cannot use this client object to send more requests.

Now we can finish this application. Because we used a durable session, it’s fine to close the client. All the requests are still on service side and will be calculated by the compute nodes in the cluster.

Monitor the progress

In HPC Cluster Manager, we can monitor the progress of the requests we just submitted. Go to Job Management to find your job, and click View Job. You can see how many requests have been processed.

Implement the client to retrieve responses

After a couple of hours, the user can come back and retrieve the results. (In our case you don’t have to wait that long.)

a. Prepare the session info. Note that you need the session ID of the previous session to help the client to attach the session.

//Input sessionId here    intsessionId;    Console.Write("Input the session id : ");    sessionId = Int32.Parse(Console.ReadLine());    //Change the headnode name here    SessionAttachInfo info = newSessionAttachInfo("head.contoso.com", sessionId);

b. Instead of creating a new session, attach to the existing session.

//Attach to session    DurableSession session = DurableSession.AttachSession(info);

c. Get responses from the session.

//Get responses    using (BrokerClient<IPrimeFactorization> client = newBrokerClient<IPrimeFactorization>(session))    {        foreach (BrokerResponse<FactorizeResponse>response in client.GetResponses<FactorizeResponse>())         {             int number = response.GetUserData<int>();             int[] factors = response.Result.FactorizeResult;             Console.WriteLine("{0} = {1}", number, string.Join<int>(" * ", factors));         }    }

 

d. Close the session.

Tips:

- Because of persistence of requests and responses, the performance of the durable session is slightly slower than that of the interactive session.

- session.Close(true) purges all the persisted data related to this session. It should only be called when the session and its data are not needed any more. If the session will be used going forward, you should call session.close(false).

- If EndRequests() is not called, the service will keep waiting for the upcoming request. After a period of time (by default, 5 mins), it will remove the client if it does not receive more requests. All the requests sent by this client will be removed.