Re: Safe multithreading in ASP.Net

From: Alvin Bruney [MVP] (vapor)
Date: 08/06/04 

Date: Thu, 5 Aug 2004 23:05:30 -0500

couple issues.

ThreadNotify.IsBackground = True
this line instructs the thread to cease all activity when the application
ends. the application doesn't end when the debugger terminates, or the
webpage is closed or session ends. so your thread will keep running.

in the event of an iis reset, your thread will end because the application
ends, but it starts as soon as a request is made which is probably why you
are seeing emails after it has ended. it's not possible for the thread to be
running when the application has ended.

basically, you need to rethink your logic because threads will always be
running as long as the webpage has received an initial request. these
threads won't stop until iis resets or asp.net detects a change to a
configuration file. 

-- 
Regards,
Alvin Bruney
[ASP.NET MVP http://mvp.support.microsoft.com/default.aspx]
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"who be dat?" <whatever@dot.com> wrote in message 
news:10h5vp3hujp9452@corp.supernews.com...
> Consider the following code which enables multithreading in an ASP.Net
> application I'm writing:
>
> Code in global.asx Application_start subroutine, Threadnotify is declared
> Globally as a new thread where it uses the address of EmailNotify below:
>
> ThreadNotify.IsBackground = True
>
> ThreadNotify.Start()
>
> --------
>
> Public Sub EmailNotify()
>
>  Dim emails As New ForumEmail
>
>  Do While ContinueNotify   'boolean value set to True so loop will 
> continue
>
>    emails.EmailNotify()
>
>    Thread.Sleep(notifyinterval * 60000)   'notifyinterval is set via app
> settings in web.config file
>
>  Loop
>
> End Sub
>
> --------------------
>
> From global.asx file in Application_End subroutine
>
> ThreadNotify.Abort()
>
>
>
> As you can probably tell, what happens is Threadnotify is started when the
> application starts.  The subroutine simply loops through and calls a
> subroutine then it pauses in intervals of minutes.  Good news: this works.
> Bad news: this works too good.  Problem is, when does this thread get
> terminated?  I can set the boolean notify in the loop to false so the 
> thread
> will reach the end of it's code and it will terminate.  However, beyond 
> this
> I have concerns.  I'm writing an application on my machine and testing it.
> I can't get that thread to stop unless I set the boolean value to false in
> that loop which is bad.  When I end the debug execution of the app, the
> thread continues and it doesn't stop.  Heck, I can stop the IIS Service 
> and
> the thread still continues to execute.  How do I know it's executing.  The
> goal of this thread is to send emails.  I'm getting emails indicating 
> which
> tells me this thread is still running.
>
> This leads to a larger issue.  When I release this application for others 
> to
> use, how can I ensure this thread won't keep running even though a user
> might end the web service?  This sucker just keeps going and going.
>
> Suppose I upload this to a production webserver.  The thread starts and
> executes fine.  Suppose I make some changes to the application code and 
> copy
> the necessary files to the production webserver.  Will the thread from the
> previous versoin of the website continue while a new thread is started by
> the updated code i.e. there will be two threads doing the same thing?
>
> The way this thread runs, I believe I can stop the webservice and destroy
> the webapplication.  The thread would still run.  This isn't acceptable.
> How do I ensure this thread stops?
>
> What is this thread running under?  I would've thought the thread would 
> run
> under IIS and consider IIS to be the parent process.  However, I'm
> terminating IIS and this thread still keeps going.  What is it running
> under?
>
> Ultimately, when the heck does this thread terminate?!  The only thing I 
> can
> do to stop this thread is to reboot the machine!  I'm scared to publish 
> this
> to my website as it may start up and never stop until they reboot their
> machines.
>
> This thread is supposed to send emails after a pause determined by the 
> user.
> Is there another way to do this?  I though about using a timer that, when 
> X
> amount of minutes passed, then the event would fire.  I could capture that
> event and execute the email code. I wasn't sure how to do this though.
> Suggestions?
>
>
>
> Thanks
>
> Chris Smith
>
>