ASP.net Plugin AppDomain issues.

  • Thread starter Thread starter zb
  • Start date Start date
Z

zb

Situation:
Using C#, ASP.Net

Requirement:
1. ASP.net application with virtual hosting service.
2. Requires a service that will run every predefined frequency in
minutes (2, 30, 100, 10000) defined in web.config and do some data
crunching in the database

How am I doing this?
I would prefer to do this (2) as a windows service but since the
service is with hosting solutions virtual hosting windows service is
out of question.
So, the hack I came up with:
For flexibility sake, the service had to be plugin model. The plugin is
derived from IPlugin (I define this) and has the obvious Run, Pause and
Stop and there is a MessageEvent (event) that is used for messaging to
the plugin framwork to log/exception etc.

Design:
In global.asax I create three static methods, one to startService,
launchService and one to stop (stopService)
When Application_start is called (when app is started) a new thread is
started from startService with method launchService which instantiates
the Plugin framework and picks up all plug-in assemblies and runs them
(calls Run method).

Idea behind this design: a new thread so the current execution is not
affected and continues to run while the new thread runs in background
processing the requirement
Plugin model so whenever a background processing is required I can
create a dll and drop it at a location and that is it.

PROBLEM:
The design's problem, if the application is running I can not "hot"
update plugin assembly while application is running since it is locked.
Through research: new AppDomain

Refer to design.
Now, the new thread creates a new appdomain and creates the plugin
framework that in turn does the Assembly.Load plugin assemblies and so
forth.
Problem, stopService can only abort/join the thread.

Question:
a. How can I stop/pause the plugin assemblies in the new thread?
b. I still can not *hot* swap/update plugin assembly? It is locked.
c. Doing appdomain.unload in stopService throws an exception see at the
end number: 1.
d. Will thread.abort /join safe enough to assume that it will call teh
stop?
e. Or is there any way the thread could know that it is being
aborted/joined and it needs to call Stop on all plugins?
f. Does joining/aborting the thread means the new appdomain will be
unloaded/nulled?

Big question:
IS THERE A BETTER WAY this can be implemented?

Thanks in advance.
PS: I will be posting this to csharp group as well, so excuse the cross
posting but the subject is such that it belongs to both groups.

Exception 1:
Type: CannotUnloadAppDomainException
Message: AppDomain can not be unloaded because the thread 1918 can not
be unwound out of it.
Stacktrace:

Server stack trace:
at System.AppDomain.nUnload(Int32 domainInternal, Thread
requestingThread)
at System.UnloadWorker.UnloadWithLock(AppDomain domain, Thread
requestingThread)
at System.UnloadWorker.Unload(AppDomain domain)
at
System.Runtime.Remoting.Messaging.StackBuilderSink.PrivateProcessMessage(MethodBase
mb, Object[] args, Object server, Int32 methodPtr, Boolean
fExecuteInContext, Object[]& outArgs)
at
System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage
msg, Int32 methodPtr, Boolean fExecuteInContext)

Exception rethrown at [0]:
at System.AppDomain.Unload(AppDomain domain)
 
2. Requires a service that will run every predefined frequency in
minutes (2, 30, 100, 10000) defined in web.config and do some data
crunching in the database
Click to expand...
Big question:
IS THERE A BETTER WAY this can be implemented?
Click to expand...

I have just this requirement for a couple of my clients' live apps. I did
the following:

1) Created a stored procedure to do the data crunching

2) Wrote a Windows service, which is deployed on my local machine, but which
connects remotely to the live SQL Server.

Now, every 30 minutes (configurable), my local service connects to the
remote live database and calls the stored procedure - that's it. Don't have
to worry about any of the problems you're experiencing.
 
Thanks Mark.

But, your suggestion will not work for me. I do not have access to db
server (I am using MySQL) from outside and keeping any process outside
the hosting environement is a no no.
 
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