I am building a search page in asp.net 3.5. Search takes a bit of time (few seconds to few minutes). Current I use AsyncMethodCaller to call Search method. AsyncMethodCaller method stores search results in Session. I user Ajax timer to check if Search method finished and then display results.
What would be the best way to implement this scenario?
I would use a Page Method from the ASP.NET Ajax Framework. It's easy to call them async and you have a callback when it's done.
Have a look here. (Async is explained at the commens of the post)
You could try the reactive extensions for .NET . I haven't tried them yet, but looks promising.
That seems perfectly fine to me, or have I missed the point of the question?
I did a similar thing recently in a PHP front-end with a search that takes about 30 seconds.
I implemented the actual search logic as a console application. The web service calls the console application to carry out the search and records the process ID of the application handling the search in the session.
An AJAX timer in the front-end polls the server every second, which checks if that process ID is still running. If it's finished, it looks in the database (where the application writes the results) and sends those back to the front-end.
If Javascript is disabled, a simple meta refresh does the same thing.
Related
I have the following use case:
A user can filter on my asp.net web project for some data and request the result as PDF. The PDF is generated per request new and returned to the user. I got already everything to run.
But: the processing can take up to two minutes and the user should be able to continue to use the page.
I tried to use a second tab, but both tabs are blocked. Even when I use the PageAsyncTask class and the async attribute. When I use a thread to perform the request, I am truly parallel, but I have no clue, how to interact with the user from inside the thread when the work is done.
How can I send an async request to the server and just get the result on the page, in whatever form, when its finished?
Dave Encosia does a great job explaining how you can do this:
Using jQuery to directly call ASP.NET AJAX page
methods
Using jQuery to Consume ASP.NET JSON Web
Services
3 mistakes to avoid when using jQuery with ASP.NET
AJAX
I created an asp.net page for waiting ajax. I have one page creating something that takes 30 seconds. On every step I change a session value.
I have another page for ajax, returning the session value for showing the percentage of creation. But, I dont know why, my ajax page awaits the end of the creation of my first page. So I only get the 100% at the end.
Maybe it's because I use VS development server and not IIS server. If this is the problem, can I change settings of the development server for asynchrone execution?
Or is it something else?
WebForms are not ideal for asynchronous operations.
Add SignalR to your project and use a Hub to push status data back to your page to update the current state of the process you are running Asynchronously.
An example of a technique to perform this type of asynchronous notification is covered in my blog post titled "A Guide to using ASP.Net SignalR with RadNotifications"
Don't use ASP.Net session state to do that. It has an implicit reader/writer lock around it, meaning your other call is probably blocking until your process finishes. You can try storing your status in a database or the cache, but it would probably be better to redesign the interaction.
I have an asp.net 3.5 web application which generates alot of audit related data. Since that data isn't immediately relevant to the user, I'd like to be able to save it to the MSSQL database asynchronously and let the user go onto the next page without waiting. I'm using Nhibernate as my ORM.
I've looked into PageAsyncTasks and as far as I can tell they simply allow you to perform page operations in parallel, but all operations still have to complete before the page finishes loading. Is there an alternative, fairly lightweight method to have asynchronous processing that will continue on without affecting page load? Is simply spinning up a new thread manually an acceptable process?
You could create a web service within your solution and when your server-side code is finished and ready to move the user on to the next page it could call your web service to do the auditing as a fire and forget type thing.
Not sure if the NHibernate session is threadsafe so if you create a new thread be careful with the context.
Ideally you could use queues and a servicebus to deal with this sort of thing safely and async but that involves architectural changes.
Not sure if this is possible but if the auditing is actually noticeably slowing the UI down maybe you'd be better off to improve that process and keep it synchronous. Either way, good luck.
Other than using a web service, is there anyway to call a method in a web app from a windows application? Both run on the same machine.
I basically want to schedule a job to run a windows app which updates some file (for a bayesian spam filter), then I want to notify the web app to reload that file.
I know this can be done in other ways but I'm curious to know whether it's possible anyway.
You can make your windows app connect to the web app and do a GET in a page that responds by reloading your file, I don't think it is strictly necessary to use a web service. This way you can also make it happen from a web browser.
A Web Service is the "right" way if you want them to communicate directly. However, I've found it easier in some situations to coordinate via database records. For example, my web app has bulk email capability. To make it work, the web app just leaves a database record behind specifying the email to be sent. The WinApp scans periodically for these records and, when it finds one with an "unprocessed" status, it takes the appropriate action. This works like a charm for me in a very high volume environment.
You cannot quite do this in the other direction only because web apps don't generally sit around in a timing loop (there are ways around this but they aren't worth the effort). Thus, you'll require some type of initiating action to let the web app know when to reload the file. To do this, you could use the following code to do a GET on a page:
WebRequest wrContent = WebRequest.Create("http://www.yourUrl.com/yourpage.aspx");
Stream objStream = wrContent.GetResponse().GetResponseStream();
// I don't think you'll need the stream Reader but I include it for completeness
StreamReader objStreamReader = new StreamReader(objStream);
You'll then reload the file in the PageLoad method whenever this page is opened.
How is the web application loading the file? If you were using a dependency on the Cache object, then simply updating the file will invalidate the Cache entry, causing your code to reload that entry when it is found to be null (or based on the "invalidated" event).
Otherwise, I don't know how you would notify the application to update the file.
An ASP.NET application only exists as an instance to serve a request. This is why web services are an easy way to handle this - the application has been instantiated to serve the service request. If you could be sure the instance existed and got a handle to it, you could use remoting. But without having a concrete handle to an instance of the application, you can't invoke the method directly.
There's plenty of other ways to communicate. You could use a database or some other kind of list which both applications poll and update periodically. There are plenty of asynchronous MQ solutions out there.
So you'll create a page in your webapp specifically for this purpose. Use a Get request and pass in a url parameter. Then in the page_load event check for this paremter. if it exists then do your processing. By passing in the parameter you'll prevent accidental page loads that will cause the file to be uploaded and processed when you don't want it to be.
From the windows app make the url Get request by using the .Net HttpWebRequest. Example here: http://www.codeproject.com/KB/webservices/HttpWebRequest_Response.aspx
I have an ASP.NET application that starts a long running operation during the Event Handler phase in the ASP.NET Page life cycle. This occurs when the end user pushes a button a bunch of queries are made to a database, a bunch of maps are generated, and then a movie is made from jpeg images of the maps. This process can take over a minute to complete.
Here's a link to the application
http://maxim.ucsd.edu/mapmaker/cbeo.aspx
I've tried using a thread from the threadpool, creating and launching my own thread and using AsyncCallback framework. The problem is that the new thread is run under a different userid. I assume the main thread is run under ASPNET, the new thread is run under AD\MAXIM$ where MAXIM is the hostname. I know this because there is an error when it tries to connect to the database.
Why is the new thread under a different userid?
If I can figure out the userid issue, what I'd like to do is check if the movie making process has finished by examining a Session variable in a Page_Load method, then add a link to the page to access the movie.
Does anyone have any good examples of using concurrency in a ASP.NET application that uses or creates threads in an EventHandler callback?
Thanks,
Matt
Did you read this?: http://msdn.microsoft.com/en-us/magazine/cc163725.aspx
Quoting one relevant portion from that link (you should read the whole thing):
A final point to keep in mind as you build asynchronous pages is that you should not launch asynchronous operations that borrow from the same thread pool that ASP.NET uses.
Not addressing the specific problem you asked about, but this is likely to come up soon:
At what point is this video used?
If it's displayed in the page or downloaded by the user, what does the generated html that the browser uses to get the video look like? The browser has to call that video somewhere using a separate http request, and you might do better by creating a separate http handler (*.ashx file) to handle that request, and just writing the url for that handler in your page.
If it's for storage or view elsewhere you should consider just saving the information needed to create the video at this point and deferring the actual work until the video is finally requested.
The problem is that the new thread is run under a different userid. I assume the main thread is run under ASPNET, the new thread is run under AD\MAXIM$ where MAXIM is the hostname.
ASPNET is a local account, when the request travels over a network it will use the computer's credentials (AD\MAXIM$).
What may be happening, is that you're running under impersonation in the request - and without in the ThreadPool. If that's the case, you might be able to store the current WindowsIdentity for the request, and then impersonate that identity in the ThreadPool.
Or, just let the ThreadPool hit the DB with Sql Authentication (username and password).