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asp.net caching : Accessing HttpContext.Current.Cache from new Thread
I have a web page that executes a potentially lengthy method declared on an object in a referenced assembly
Nested within this method is a call to a static method which retrieves values from cache via the HttpContext.Current.Cache object In order to make the web application more responsive, I am now trying to execute this long running method in a new thread My problem: When the process running on the new thread reaches the reference to the HttpContext.Current.Cache object in the static method I get a runtime exception saying "Object reference not set to an instance of an object."
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>When the process running on the new thread reaches the reference to the > >HttpContext.Current.Cache object in the static method I get a runtime > >exception saying "Object reference not set to an instance of an object." You will need to pass a reference to the httpcontext to the thread. That's the only way this will work because the thread is not allowed to manipulate the context object since it belongs to the main thread. [quoted text, click to view] >Educated guess: I'm thinking I need to establish the context of the new > >thread to be the same as that of the web page which spawns the thread. > >Am I headed in the right general direction? Can anyone offer any specific > >example or explanation of how to implement multi-threading with access >to >the web application cache? yup, something like that. The way you establish context is by passing in a reference to child thread from the main thread. You can do this in your thread class constructor public class thread { public start(HttpConstext current).... the call would be something like thread t = new thread(HttpContext.Current) -- Regards, Alvin Bruney [ASP.NET MVP http://mvp.support.microsoft.com/default.aspx] Got tidbits? Get it here... http://tinyurl.com/27cok [quoted text, click to view] "Ken Everett" <keverett@troygroup.com> wrote in message news:BB404153-134C-4E2B-A57D-E5F24ADADECE@microsoft.com... >I have a web page that executes a potentially lengthy method declared on an >object in a referenced assembly. > > Nested within this method is a call to a static method which retrieves > values from cache via the HttpContext.Current.Cache object. > > In order to make the web application more responsive, I am now trying to > execute this long running method in a new thread. > > My problem: When the process running on the new thread reaches the > reference to the HttpContext.Current.Cache object in the static method I > get a runtime exception saying "Object reference not set to an instance of > an object.". > > Educated guess: I'm thinking I need to establish the context of the new > thread to be the same as that of the web page which spawns the thread. Am > I headed in the right general direction? Can anyone offer any specific > example or explanation of how to implement multi-threading with access to > the web application cache?
Thanks for the reply. However, I'm not sure I'm clear on the details of
your suggestion. Are you implying that I should create my own thread class that inherits from System.Threading.Thread and override the Start method? Or do I try something like this: MyClass myObject = new MyClass(); Thread myThread = new Thread( new ThreadStart( myObject.LongMethod( HttpContext ) )); *** Sent via Developersdex http://www.developersdex.com ***
Alvin is correct, of course, but let me add something just in case: if your
separate thread intends to interact with the original page, it will have a problem, as the page will be gone by the time the thread finishes. In fact, although it makes sense that accessing HttpContext.Current.Cache will work after the request is complete, I'd be careful about using any other part of the HttpContext object from a separate thread. That's the context of the request, and if the request is over, you have to wonder what's in the context... -- John Saunders John.Saunders at SurfControl.com [quoted text, click to view] "Alvin Bruney [MVP]" <vapor at steaming post office> wrote in message news:ucHjaDfMEHA.2592@tk2msftngp13.phx.gbl... > >When the process running on the new thread reaches the reference to the > > >HttpContext.Current.Cache object in the static method I get a runtime > > >exception saying "Object reference not set to an instance of an object." > > You will need to pass a reference to the httpcontext to the thread. That's > the only way this will work because the thread is not allowed to manipulate > the context object since it belongs to the main thread. > > >Educated guess: I'm thinking I need to establish the context of the new > > >thread to be the same as that of the web page which spawns the thread. > > >Am I headed in the right general direction? Can anyone offer any specific > > >example or explanation of how to implement multi-threading with access >to > >the web application cache? > > yup, something like that. The way you establish context is by passing in a > reference to child thread from the main thread. You can do this in your > thread class constructor > > public class thread > { > public start(HttpConstext current).... > > the call would be something like thread t = new thread(HttpContext.Current) > > -- > Regards, > Alvin Bruney > [ASP.NET MVP http://mvp.support.microsoft.com/default.aspx] > Got tidbits? Get it here... http://tinyurl.com/27cok > "Ken Everett" <keverett@troygroup.com> wrote in message > news:BB404153-134C-4E2B-A57D-E5F24ADADECE@microsoft.com... > >I have a web page that executes a potentially lengthy method declared on an > >object in a referenced assembly. > > > > Nested within this method is a call to a static method which retrieves > > values from cache via the HttpContext.Current.Cache object. > > > > In order to make the web application more responsive, I am now trying to > > execute this long running method in a new thread. > > > > My problem: When the process running on the new thread reaches the > > reference to the HttpContext.Current.Cache object in the static method I > > get a runtime exception saying "Object reference not set to an instance of > > an object.". > > > > Educated guess: I'm thinking I need to establish the context of the new > > thread to be the same as that of the web page which spawns the thread. Am > > I headed in the right general direction? Can anyone offer any specific > > example or explanation of how to implement multi-threading with access to > > the web application cache? > >
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> Thread myThread = new Thread( new ThreadStart( myObject.LongMethod( Yes.> HttpContext ) )); More important than what I said is John's reply. The page is gone by the time you make the cache access. You will need to do a join on the main thread to keep the page waiting for the thread to accomplish its mission otherwise when the child thread is ready with its results, the boat would have sailed away long ago. If you can't cause the main thread to wait for the child thread to finish, it makes no sense to thread basically. -- Regards, Alvin Bruney [ASP.NET MVP http://mvp.support.microsoft.com/default.aspx] Got tidbits? Get it here... http://tinyurl.com/27cok [quoted text, click to view] "Ken Everett" <keverett@troygroup.com> wrote in message news:Ot3EmGgMEHA.2244@TK2MSFTNGP10.phx.gbl... > Thanks for the reply. However, I'm not sure I'm clear on the details of > your suggestion. > > Are you implying that I should create my own thread class that inherits > from System.Threading.Thread and override the Start method? > > Or do I try something like this: > > MyClass myObject = new MyClass(); > > Thread myThread = new Thread( new ThreadStart( myObject.LongMethod( > HttpContext ) )); > > > > > > *** Sent via Developersdex http://www.developersdex.com *** > Don't just participate in USENET...get rewarded for it!
ThreadStart delegate wraps a method with NO parameters
So you might need to save the reference to HttpContext.Current.Cache to a global variable and access it from the new thread. Did I mention synchronization ? Thank
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"Ramesh Nayanala" <anonymous@discussions.microsoft.com> wrote in message news:5086D126-AE33-4DC1-83D4-C49398011FB9@microsoft.com... > ThreadStart delegate wraps a method with NO parameters. > So you might need to save the reference to HttpContext.Current.Cache to a global variable > and access it from the new thread. > Did I mention synchronization ? public class MyClass { private HttpContext _ctx; public MyClass(HttpContext ctx){_ctx = ctx;} public void Start() { ThreadStart start = new ThreadStart(MainThreadRoutine); Thread.Start(start); } private void MainThreadRoutine() { // Do something lengthy using the HttpContext in _ctx // ... // But by the time you get here, it's all over, and _ctx is meaningless, because the request is OVER // and you missed the boat! } } // In your page class: private void Page_Load(object sender, EventArgs e) { MyClass myClass = new MyClass(HttpContext.Current); myClass.Start(); } What you're trying to accomplish cannot be accomplished easily in ASP.NET 1.0 or 1.1. According to the latest issue of MSDN Magazine, MS appear to have a partial solution for this problem in ASP.NET 2.0. In the meantime, I recommend that you finish every other part of your application before returning to this "multiple threads in ASP.NET" issue. When everything else is done, you can spend some time reinventing the wheel. -- John Saunders John.Saunders at SurfControl.com
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