I'm managing a rather large project, written in asp.net webforms + mvc3, with a large user base, and a pretty high daily visitor count. Basically, there are a lot of requests at any given moment.
One of my controllers in MVC that handles / resizes images on the fly has the following attribute applied to it:
[SessionState(SessionStateBehavior.Disabled)]
Now, if an action in the controller tries to access the session - it obviously throws an exception - so we're good so far.
The problem is: if I go to the IIS Worker Processes window (Win Server 2008 R2, IIS 7.5), and check the current requests for this site, I can sometimes see the requests to an action in this controller. Their current state is locked in State: RequestAcquireState, Module Name: Session. Sometimes these locks go over a second or two in this state.
Wasn't the whole point of the attribute in the first place to make the requests to the controller ignore the state, and not waste time (and possibly being locked) trying to acquire the state?
If this is so - am I doing something wrong here, or does the problem lie elsewhere?
[migrated from comments]
If you're using a custom controller factory or route handler, make sure that they're aware of the controller's session state behavior. Marking a controller as not requiring session state requires cooperation from both of these components. Out-of-box, the DefaultControllerFactory and MvcRouteHandler are designed to work with this. See DefaultControllerFactory.GetControllerSessionBehavior and MvcRouteHandler.GetHttpHandler for more information. If you're writing custom components, you can use those methods as inspiration.
Related
I created a service with a RESTful API in ASP.NET, hosted in IIS. Inside this service, I would like to create an actor system with Akka.NET.
Upon creating the actor system:
var actorSystem = ActorSystem.Create("myActorSystem");
The following exception is thrown:
A first chance exception of type 'System.InvalidOperationException' occurred in System.Web.dll
Additional information: An asynchronous operation cannot be started at this time. Asynchronous operations may only be started within an asynchronous handler or module or during certain events in the Page lifecycle. If this exception occurred while executing a Page, ensure that the Page is marked <%# Page Async="true" %>. This exception may also indicate an attempt to call an "async void" method, which is generally unsupported within ASP.NET request processing. Instead, the asynchronous method should return a Task, and the caller should await it.
The actor system is inherently a concurrent system with asynchronous messages being exchanged between actors. As explained here, this actor system would not survive IIS taking down the AppDomain, which is probably why the aforementioned exception is thrown.
This article explains how to run background tasks in ASP.NET. However, I don't see how I could use this for my actor system, as I have no control over the lifecycle of background tasks that might be created by Akka.NET.
Is there a way to make this work, or should I abandon the idea of having an actor system in an ASP.NET application?
EDIT: I also saw a question on Stackoverflow about implementing a REST service using Akka. Any advice about a solution similar to the Spray toolkit, but working for Akka.NET would be welcome.
I've used Akka.NET and Akka.Remote inside ASP.NET MVC applications that are doing up to 1000 requests per second on EC2 - so I'll share some of the tips and tricks I used to get it up and running successfully. Had a prototype version that even used Akka.Cluster but ended up not shipping that version.
Best place to call ActorSystem.Create is inside Global.asax Application_Start().
Hang onto a static reference to the ActorSystem object inside Global.asax itself, using a static field or property. Helps ensure that the ActorSystem itself doesn't get garbage-collected in long-running applications.
Create a separate static helper class to initialize any top-level actors your applications needs - i.e. actors at the top of the /user/ hierarchy. This class should also provide actor paths that your ASP.MVC controllers and action methods can use for Tell and Ask operations.
Creating the ActorSystem is a bit of an expensive operation, because lots of system-level stuff gets fired up at once. It's definitely best to do this once at application startup and then just cache the result inside the Application class.
Creating individual actor instances is cheap - you should be able to do this no-problem inside ASP.NET MVC action methods. If you see this error come up again, please let us know what part in the request-handling process this error occurred and with which version of ASP.NET.
Edit: added some updated guidance for how to do this on ASP.NET Core
https://petabridge.com/blog/akkadotnet-aspnetcore/
Keep your ActorSystem as a shared property in some static class container - this way you may access it from the rest of your application. Actor system initialization/disposal can be done by:
Global.asax - use ActorSystem.Create(...) inside Global.asax Application_Start and dispose it with system.Shutdown() on Application_End.
OWIN - create actor system in OWIN's Startup.Configuration method and shut it down by binding to host.OnAppDisposing event (how-to link).
Remember that IIS will startup your web app only after first request and tear it down automatically after some time when it's idle. Therefore make sure, that your deployment script will ping application after publishing and set idle timeout (link) for long enough if you want your Akka actor system to run continuously.
Second option
Separate your Actor System logic and deploy it, for example, as a Windows Service (or Linux deamon). Turn on Akka.Remoting for it and create a proxy client, which will forward all application long-running sensitive tasks to external service. Similar solution is often used for things such as schedulers or event buses, when your application logic must be working continuously.
I am trying to understand the various ways of storing and instantiating Application (i.e. objects available to every user) and Session level (objects created and available to users only for their session) variables. Also, how does OWIN fit into all of this?
Global.asax.cs - This can contain a bunch of different methods. I believe that Application_Start is only called during the first request. However, there are a few candidates here for methods to populate session level variables (e.g. Session_Start and Application_BeginRequest). What is the standard way of doing this?
There is also the Startup class used by OWIN. I get that OWIN lets you store Application level variables, but why wouldn't you just use the HttpApplicationState Application variable accessible from Global.asax.cs to accomplish this? Also - can OWIN handle Session variables?
"I believe that Application_Start is only called during the first
request."
Only for the first request after calling the web application. For instance, this is the case after deploying, ApplicationPool Recycling, restarting or coming out of sleep.
Let's assume 3 users visit your web application. Application_Start will only be called for one of them, specifically the first one that visits it. Therefore it is not suited for populating user-specific session values.
However, there are a few candidates here for methods to populate session level variables (e.g. Session_Start and Application_BeginRequest). What is the standard way of doing this?
In the past I've worked with Session_Start to initialize user-specific session values (like default values) on numerous projects and never had an issue with it.
I'm really not sure what the question is, as I said in the comments. I'm going to ignore the OWIN stuff since I don't know, frankly.
Firstly, try not to store state at all. Design to pass state back and forth between server and client in models, or the URL, even in the HTML on the client such as in the URLs in the <a> tags your rendering, or (rarely) in cookies, rather than keep things in memory. Stateless designs are way more scalable.
Storing state isn't "usually" done in the Global.asax but then what's usual? I store state as and when I need it, load it or otherwise come by that data. For me in MVC, that's usually downstream of a Controller action, maybe while logging someone in, or reading some data received in a model, like a customer clicking 'add to cart'.
Application state I rarely use, though I store long-lived and shared data within normal fields and properties in long-lived static classes. These die when the app is recycled, but I don't usually care since the apps are designed to work without it, stateless; its usually cached bits of data.
Also, Session_Start only fires when a new browser/agent hits the site. You don't know the user at that point.
The methods in the Global.asax were not specifically designed for 'bootstrapping' state-loading, they're just convenient events for doing whatever you want with. You don't have to use them at all, mine usually just contain logging so I know when sessions start etc.!
I don't know if this helps.
Once you have a plan, come back and ask a targeted question about the OWIN stuff.
I've created web application that has a sub that builds a contacts list. This sub fetches phone numbers and email address from a contacts db based on ids that are provided by a user. At it's fastest, the application will process about four ids per second. With 200-300 ids at any given time, the completion time is long.
Time is not really the problem, it's end user status updates. I've created a very crude web service that reads the "CurrentRecordNumber" that is stored in a session variable as the app loops through the ids. I intend to use javascript to call the webmethod from the app periodically to update status.
My problem is that when debugging, the webmethod call will complete successfully, but not until the app is finished processing.
This seems like a very simple problem. I must not be using the right terms because my results seem overly complicated.
I'm very new to asynchronous features of ASP.NET so please forgive. I have, however, written some Winforms that incorporate multiple threads so I have a basic understanding of threading.
This is due to the way ASP.NET treats session. You haven't said whether you are using webforms or MVC, but MVC has a quick workaround for this.
First, the problem:
SessionState is designed to be accessed by one request at a time, in the order received by the server. Think of this as a queue at the bank with only one bank teller available. The first person in line is the first to be helped (though this is on a per-session basis, not a per-user).
ASP.NET locks all other requests that require SessionState from executing until the previous one is done.
I haven't tried to correct this problem in web forms, but the easiest way I know of would be to not require SessionState on your progress check.
In MVC, there's a SessionState attribute that can be applied to the controller or method, indicating that there's no chance of a call to that method overwriting SessionState. As long as your call is read-only, you can make your controller code use this attribute to allow multiple async requests simultaneously:
<SessionState(SessionStateBehavior.ReadOnly)>
Public Class MyController
We have a flex application that connects to a proxy server which handles authentication. If the authentication has timeout out the proxy server returns a json formatted error string. What I would like to do is inspect every URLRequest response and check if there's an error message and display it in the flex client then redirect back to login screen.
So I'm wondering if its possible to create an event listener to all URLRequests in a global fashion. Without having to search through the project and add some method to each URLRequest. Any ideas if this is possible?
Unless you're only using one service, there is no way to set a global URLRequest handler. If I were you, I'd think more about architecting your application properly by using a delegate and always checking the result through a particular service which is used throughout the app.
J_A_X has some good suggestions, but I'd take it a bit farther. Let me make some assumptions based on the limited information you've provided.
The services are scattered all over your application means that they're actually embedded in multiple Views.
If your services can all be handled by the same handler, you notionally have one service, copied many times.
Despite what you see in the Adobe examples showing their new Service generation code, it's incredibly bad practice to call services directly from Views, in part because of the very problem you are seeing--you can wind up with lots of copies of the same service code littered all over your application.
Depending on how tightly interwoven your application is (believe me, I've inherited some pretty nasty stuff, so I know this might be easier said than done), you may find that the easiest thing is to remove all of those various services and replace them by having all your Views dispatch a bubbling event that gets caught at the top level. At the top level, you respond to that event by calling one instance of your service, which is again handled in one place.
You may or may not choose to wrap that single service in a delegate, but once you have your application archtected in a way where the service is decoupled from your Views, you can make that choice at any time.
Would you be able to extend the class and add an event listener in the object's constructor? I don't like this approach but it could work.
You would just have to search/replace the whole project.
I'm making a .net component, resulting in a dll assembly, that will be referenced by an asp.net site, and in another project by an asmx webservice. All code is version 2.0.
The component has a few functions that call an external webservice, which returns an object. One of these functions is for example Login(username, password), which generates amongst others a unique session id for this user. The resulting information and session id are stored in variables in the component.
The issue in the website is:
When the user logs in in the frontend, and my component gets called and checks the login and generates the session id, I want that information in my component to persist when the user browses to another page in the site.
The issue in the web service using my component is:
I don't really care much about session state, but I want the component to just work. If per call a new session id is generated, that's okay.
The combination of the two environments causes the following problem for me:
I can't use the asp.net Session() variable in my component without referencing system.web, which is kinda silly and might not be available in the web service project that includes my component
I can't program my component as a singleton, because then in the website application, it's shared amongst all visitors, overwriting sessions and whatnot
making an array of "session information" in my component and maintaining that is hard to program (when does it get invalidated?) and might not work in a web farm environment
Is there a solution to this situation? Or should I make two instances of my component, one for use in websites, and one for use in web services?
Perhaps I'm not understanding what your asking but why can't you do something like:
Component.Login(user,pass);
Session["Component"] = Component.SessionID
I've created an extra class "Factory" which has a .Create(byref Session as HttpSessionState), that looks if the passed in session object is Nothing, if not, it checks if there is a Component object in it, if so, it uses it, if not, it creates it and adds it to the session.
In the case of the webservice call, the factory gets the Nothing-parameter, so it doesn't check in the session object. It seems to work.
Thanks for your answers!