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session variable and asynchrous callI have an ASP.NET web application on a corporate intranet which retrieves some user information it uses from a webservice. The data does not change often, but when it does, my site needs the updated information. The connection to the database is slow and occasionally unreliable. To avoid problems, we are storing the needed information in cookies that do not expire for over 10 years. We use the cookie values in the absence of "better information". Periodically we'd like to update the cookie values. Our approach is to include an additional cookie that expires weekly. When a user returns to our site, we check for the presence of this cookie, if it is not present (new user or expired cookie) we need to query the webservice. This can take long to return (or may timeout), and we cannot make our users wait. BTW, all of this processing occurs in a PreRequestHandlerExecute event handler method of an HTTP module. In order to refresh the data without waiting, I would like to call the web service asynchronously. I have written the code to use an HttpWebRequest object and call the BeginGetRequestStream method. I have a callback function that parses the responsestream and extracts the data I need. I need to put this data into cookies. I can wait until the next request/response cycle. My question is this: Since the callback function may not be invoked until after the response has been streamed to the client, where can I put the information I've retrieved? I've tried adding a reference to the current session to my state object. I then store the information in Session variables using the state object. This works while the cal back function is executing (the values exist in session variables). The values are gone when the next request cycle is processed. Am I doing something wrong? Is this not a viable approach? If not, where can I store this data in the case that the response has already been streamed to the client? Again, any advice would be appreciated. You should look into caching your data in the ASP.Net Cache. When you
add the item to cache, you can specify a duration and a method to call when the cached value expires. Then you can reload the data in the background without affecting the users. Bryan Phillips MCSD, MCDBA, MCSE Blog: http://bphillips76.spaces.live.com Show quote "carro***@gmail.com" <carro***@gmail.com> wrote in message news:1161902882.460605.218100@i3g2000cwc.googlegroups.com: > Here's my scenario. Please advise me if you can. > > I have an ASP.NET web application on a corporate intranet which > retrieves some user information it uses from a webservice. The data > does not change often, but when it does, my site needs the updated > information. The connection to the database is slow and occasionally > unreliable. To avoid problems, we are storing the needed information > in cookies that do not expire for over 10 years. We use the cookie > values in the absence of "better information". Periodically we'd like > to update the cookie values. Our approach is to include an additional > cookie that expires weekly. When a user returns to our site, we check > for the presence of this cookie, if it is not present (new user or > expired cookie) we need to query the webservice. This can take long to > return (or may timeout), and we cannot make our users wait. BTW, all > of this processing occurs in a PreRequestHandlerExecute event handler > method of an HTTP module. > > In order to refresh the data without waiting, I would like to call the > web service asynchronously. I have written the code to use an > HttpWebRequest object and call the BeginGetRequestStream method. I > have a callback function that parses the responsestream and extracts > the data I need. I need to put this data into cookies. I can wait > until the next request/response cycle. > > My question is this: Since the callback function may not be invoked > until after the response has been streamed to the client, where can I > put the information I've retrieved? I've tried adding a reference to > the current session to my state object. I then store the information > in Session variables using the state object. This works while the cal > back function is executing (the values exist in session variables). > The values are gone when the next request cycle is processed. > > Am I doing something wrong? Is this not a viable approach? If not, > where can I store this data in the case that the response has already > been streamed to the client? > > Again, any advice would be appreciated. Bryan,
I am quite familiar with caching, but I'm not sure this will work. The data I'm retrieving is specific to each user. This is why I'm choosing cookies as my data store. I can temporarily (until the next request/response cycle) place these somewhere else, as long as I can get back to the values in the next cycle. In order to scope these to the current user, session variables seemed like the logical answer, but this doesn't appear to work under these conditions. I'm willing to entertain other solutions as well. Again the heart of the problem is that the data retrieval may take a while to complete. I am requesting this data asynchronously so the user is not impacted. However the callback may not be invoked until after the response has been streamed to the user. Is there some place I can store the data that will be in the user's scope on the next request/response cycle? Bryan Phillips wrote: Show quote > You should look into caching your data in the ASP.Net Cache. When you > add the item to cache, you can specify a duration and a method to call > when the cached value expires. Then you can reload the data in the > background without affecting the users. > > Bryan Phillips > MCSD, MCDBA, MCSE > Blog: http://bphillips76.spaces.live.com > > > > > "carro***@gmail.com" <carro***@gmail.com> wrote in message > news:1161902882.460605.218100@i3g2000cwc.googlegroups.com: > > > Here's my scenario. Please advise me if you can. > > > > I have an ASP.NET web application on a corporate intranet which > > retrieves some user information it uses from a webservice. The data > > does not change often, but when it does, my site needs the updated > > information. The connection to the database is slow and occasionally > > unreliable. To avoid problems, we are storing the needed information > > in cookies that do not expire for over 10 years. We use the cookie > > values in the absence of "better information". Periodically we'd like > > to update the cookie values. Our approach is to include an additional > > cookie that expires weekly. When a user returns to our site, we check > > for the presence of this cookie, if it is not present (new user or > > expired cookie) we need to query the webservice. This can take long to > > return (or may timeout), and we cannot make our users wait. BTW, all > > of this processing occurs in a PreRequestHandlerExecute event handler > > method of an HTTP module. > > > > In order to refresh the data without waiting, I would like to call the > > web service asynchronously. I have written the code to use an > > HttpWebRequest object and call the BeginGetRequestStream method. I > > have a callback function that parses the responsestream and extracts > > the data I need. I need to put this data into cookies. I can wait > > until the next request/response cycle. > > > > My question is this: Since the callback function may not be invoked > > until after the response has been streamed to the client, where can I > > put the information I've retrieved? I've tried adding a reference to > > the current session to my state object. I then store the information > > in Session variables using the state object. This works while the cal > > back function is executing (the values exist in session variables). > > The values are gone when the next request cycle is processed. > > > > Am I doing something wrong? Is this not a viable approach? If not, > > where can I store this data in the case that the response has already > > been streamed to the client? > > > > Again, any advice would be appreciated. Eureka! I've got it.
Apparently there is a feature of ASP.Net such that if there is no value stored in session state, there is nothing saved on the server. This makes sense when you think about it. Why allocate storage space to a session with nothing in it? Apparently the decision to not store values is made before my callback function. Despite that I was able to write values to session variables in the callback function, these were not available when the next request cycle began. I've read several articles that discuss this behavior under other symptoms. Typically those involved lost session variables. In each of those cases, the session id was different from one request/response cycle to the next. In my case, the session ID was the same every time, but the variables were not present if the asynchronous callback occurred after the response had been sent to the client. The solution in this case was to add a dummy session variable just prior to firing the asynchronous call (Application.Session["DUMMY"] = String.Empty;). This ensures that the session has some state information and causes the decision to preserve the session state to be true. The acutal saving (I assume) does not occur until the session is about to be destroyed. When my callback function is invoked, I am able to retrieve the reference to my session that I had stored in the AsyncState. I can then write my additional variables to the session state. Now however, these values are present when the next request cycle begins. I have additional code that checks for the presence of these variables on the next request to this session. If they are present, they are added to cookies that will not expire for a week, avoiding the need to repeat this lengthy process for some time. Hope this helps someone. carrolky wrote: Show quote > Bryan, > > I am quite familiar with caching, but I'm not sure this will work. The > data I'm retrieving is specific to each user. This is why I'm choosing > cookies as my data store. I can temporarily (until the next > request/response cycle) place these somewhere else, as long as I can > get back to the values in the next cycle. In order to scope these to > the current user, session variables seemed like the logical answer, but > this doesn't appear to work under these conditions. I'm willing to > entertain other solutions as well. > > Again the heart of the problem is that the data retrieval may take a > while to complete. I am requesting this data asynchronously so the > user is not impacted. However the callback may not be invoked until > after the response has been streamed to the user. Is there some place > I can store the data that will be in the user's scope on the next > request/response cycle? > > > Bryan Phillips wrote: > > You should look into caching your data in the ASP.Net Cache. When you > > add the item to cache, you can specify a duration and a method to call > > when the cached value expires. Then you can reload the data in the > > background without affecting the users. > > > > Bryan Phillips > > MCSD, MCDBA, MCSE > > Blog: http://bphillips76.spaces.live.com > > > > > > > > > > "carro***@gmail.com" <carro***@gmail.com> wrote in message > > news:1161902882.460605.218100@i3g2000cwc.googlegroups.com: > > > > > Here's my scenario. Please advise me if you can. > > > > > > I have an ASP.NET web application on a corporate intranet which > > > retrieves some user information it uses from a webservice. The data > > > does not change often, but when it does, my site needs the updated > > > information. The connection to the database is slow and occasionally > > > unreliable. To avoid problems, we are storing the needed information > > > in cookies that do not expire for over 10 years. We use the cookie > > > values in the absence of "better information". Periodically we'd like > > > to update the cookie values. Our approach is to include an additional > > > cookie that expires weekly. When a user returns to our site, we check > > > for the presence of this cookie, if it is not present (new user or > > > expired cookie) we need to query the webservice. This can take long to > > > return (or may timeout), and we cannot make our users wait. BTW, all > > > of this processing occurs in a PreRequestHandlerExecute event handler > > > method of an HTTP module. > > > > > > In order to refresh the data without waiting, I would like to call the > > > web service asynchronously. I have written the code to use an > > > HttpWebRequest object and call the BeginGetRequestStream method. I > > > have a callback function that parses the responsestream and extracts > > > the data I need. I need to put this data into cookies. I can wait > > > until the next request/response cycle. > > > > > > My question is this: Since the callback function may not be invoked > > > until after the response has been streamed to the client, where can I > > > put the information I've retrieved? I've tried adding a reference to > > > the current session to my state object. I then store the information > > > in Session variables using the state object. This works while the cal > > > back function is executing (the values exist in session variables). > > > The values are gone when the next request cycle is processed. > > > > > > Am I doing something wrong? Is this not a viable approach? If not, > > > where can I store this data in the case that the response has already > > > been streamed to the client? > > > > > > Again, any advice would be appreciated.  |
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