Sitecore Pipeline Singleton

Question

We have multi-step form hosted in sitecore 8.2. As user fills up each step and click on next, our custom pipeline gets invoked. For each steps we have corresponding pipelines. Each pipeline updates the session data as user progresses.

Problem:

During performance test, we noticed that if a user clicks the next button exactly at same time the their session data gets overwritten with other user's data.

Came across this blog post which talks about Processors being Singlon Lifecycle: https://ctor.io/be-careful-with-sitecore-pipeline-processors-lifecycle/

Questions:

Why pipelines are designed to be singleton lifecycle? This issue only occurs if more than 1 user happens the click next button exactly at same time.

Code snippet

namespace MyPipeline
{
    public class Initialize
    {
        private readOnly ISessionStore _sessionStore;

        public Initialize(ISessionStore sessionStore)
        {
            this._sessionStore = sessionStore;
            Sitecore.Diagnostics.Log.Info("ctor() has been called", this);
        }

        public override void Process(EmployeePipelineArgs args)
        {

            _sessionStore.SetSessionData(EmployeePipelineArgs);

        }
    }
}

namespace MyPipeline
{
    public class SessionTest
    {
        private readOnly ISessionStore _sessionStore;

        public LifecycleTest(ISessionStore sessionStore)
        {
            this._sessionStore = sessionStore;
            Sitecore.Diagnostics.Log.Info("ctor() has been called", this);
        }

        public override void Process(CustomPipelineArgs args)
        {
            var mySessionData = _sessionStore.GetSessionData()
            Sitecore.Diagnostics.Log.Info(mySessonData.Name);

        }
    }
}

Snippet for SetSessionData

 public class SessionStore : ISessionStore
{
    private readonly IHttpContextWrapper _httpContext;

    public SessionStore(IHttpContextWrapper httpContext)
    {
         _httpContext = httpContext;
    }

    public override void SetSessionData(data)
    {

        _httpContext.Current.Session[somekey] = data;
    }
}


public class HttpContextWrapper : IHttpContextWrapper
{
    public HttpRequest Request =>  HttpContext.Current.Request;
    public HttpResponse Response => HttpContext.Current.Response;
    public HttpContext Current => HttpContext.Current;
}

Configuration

<?xml version="1.0"?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <pipelines>
      </pipelinetest>
        <processor type="MyPipeline.Initialize, MyPipeline" resolve ="true" />
        <processor type="MyPipeline.SessionTest, MyPipeline" resolve ="true" />     
      </pipelinetest>

    </pipelines>
  </sitecore>
</configuration>

Thanks.

Answer 1

I don't think anyone can answer question Why pipelines are designed to be singleton lifecycle? except from whoever came with idea of Sitecore pipelines.

From my understanding, pipelines are used in Sitecore everywhere. In most crucial parts of Sitecore, where even milliseconds matter. Creating new object for every single processor when any pipeline is started would be just waste of time.

In my opinion, pipeline processors should be kind of "stateless". They shouldn't have any single-execution-specific data in their properties. Everything they work on should be passed via arguments of the Process method.

I would expect that your ISessionStore uses something like HttpContext.Current.Session everytime it sets or gets something from session. But if you've created a Session property in ISessionStore and set the value of it to session from httpcontext, then the problem is here. I cannot tell this for sure without seeing the code of your ISessionStore implementation.