Hi Guys,
I've run into something which I'm struggling to explain. My
actual example is quite complicated, and will be difficult
to post here without a fairly large chunk of code being
posted, so I'll do my best to explain in words:
Basically, in a thick / smart client application, I am
trying to perform a login asynchronously. The result of the
login is that an instance of a custom class (let's call it
MyPrincipal) gets assigned to Thread.CurrentPrincipal. Now,
it might be reasonable to assume that since we are on a
background thread, once this operation completes, accessing
Thread.CurrentPrincipal from another thread (primarily the
UI thread) might not return the MyPrincipal instance.
OK, so the solution is to set Thread.CurrentPrincipal on the
BackgroundWorker.RunWorkerCompleted, right? Well, it
doesn't seem to change anything. No exception is thrown,
but somehow Thread.CurrentPrincipal just seems to lose its
value somewhere between my code setting it, and the next
time I trigger an event on the UI. At first, I thought this
might be an issue with how BackgroundWorker was implemented,
so I invoked a method on the UI thread explicitly using a
delegate. Same behavior!?
As a work around, I have now resorted to retrieving the
MyPrincipal object on the BackgroundWorker, and then setting
a class variable to it. I then enable a Windows.Forms.Timer
with a short duration (10 ms), which then sets
Thread.CurrentPrincipal when the Tick event fires (this is
on the UI thread since it’s a WinForms timer). This works
100%, but it's just a bit too cheesy for me to leave in as
production code.
Is there something I'm missing about threads and / or
specifically Thread.CurrentPrincipal? Am I supposed to be
using a lock() on it, even though there is only a single
thread at any given point which is accessing it? And what
exactly is the difference between RunWorkerCompleted,
Control.Invoke, and a timer's tick event, since it seems to
be making a large difference. My only thought at this point
is that it's some kind of timing issue, but I'm not really
sure why it would occur.
BTW, I ran across this thread with someone experiencing
basically the same issue, in the thread they agree that it's
strange but can't really explain why it happens either:
http://groups.google.com/group/micros
oft.public.dotnet.languages.csharp/browse_thread/thread/fe12
e17030778c70/7b18d3efff24cc22?lnk=raot
Any ideas would be welcome....
Regards,
Daniel.
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