Multithreaded access with TableAdapters

1 Feb 2006 1:10 PM

the whip

We have an app under development processing data from com port events. There
can be multiple com ports all sending data back to this one method on one
instance of a class â€œldâ€. This method gets a db object associated
speciffically with THAT com port. The db objects wrap a datatable and a
tableadapter.
So if we have COM1, and COM3 in use we might have something like this

ld -> retrieves    ->    dataAdapterObjCOM1
            dataAdapterObjCOM3

If I am running with only one com port all works fine. With more than one I
get many errors in the Designer class for the db stuff. All the db objects
are separate instance of objects specifically associated with that com port.
So no two threads should be trying to access the same db wrapper objects at
the same time.

The errors include:
The connection was not closed. The connection's current state is connecting.
When trying to insert with the adapater.
    Note: I am testing for this connection state right before the insert line
and sometimes it will see it sometimes it wonâ€™t. I know doc says its for
future use but I am getting it now.
Object reference not set to an instance of an object. on DataTable NewRow()

I unplug the extra comport and everything works fine again.

Any suggestions?

1 Feb 2006 1:31 PM

Miha Markic [MVP C#]

Hi there,

DataAdapter, DataTable etc. are not thread safe.
Plus, if your DataTable is bound to an UI control then you can modify its
data only from within UI thread.
Plus, you have to make sure that you don't use same connection instance when
two threads require it.

--
Miha Markic [MVP C#]
RightHand .NET consulting & development www.rthand.com
Blog: http://cs.rthand.com/blogs/blog_with_righthand/

Show quote

"the whip" <the w***@discussions.microsoft.com> wrote in message
news:8A8E0FB7-1F70-4CD9-8412-D27785A89831@microsoft.com...
> We have an app under development processing data from com port events.
> There
> can be multiple com ports all sending data back to this one method on one
> instance of a class "ld". This method gets a db object associated
> speciffically with THAT com port. The db objects wrap a datatable and a
> tableadapter.
> So if we have COM1, and COM3 in use we might have something like this
>
> ld -> retrieves -> dataAdapterObjCOM1
> dataAdapterObjCOM3
>
> If I am running with only one com port all works fine. With more than one
> I
> get many errors in the Designer class for the db stuff. All the db
> objects
> are separate instance of objects specifically associated with that com
> port.
> So no two threads should be trying to access the same db wrapper objects
> at
> the same time.
>
> The errors include:
> The connection was not closed. The connection's current state is
> connecting.
> When trying to insert with the adapater.
> Note: I am testing for this connection state right before the insert line
> and sometimes it will see it sometimes it won't. I know doc says its for
> future use but I am getting it now.
> Object reference not set to an instance of an object. on DataTable
> NewRow()
>
> I unplug the extra comport and everything works fine again.
>
> Any suggestions?
>

2 Feb 2006 3:31 PM

the whip

That is what confuses me. Since each thread has its own instance of a
table&tableadapter wrapper object I shouldn't technically be doing
multithreaded access, right? At least not multithreaded in the sense of two
threads accessing the same instance of a tableadapter. note- It is not UI
bound.

Can anyone point me to some examples on managing connections in a
multithreaded situation? Right now my connection is defined in the
app.config, and every table adapter refers to that connection string. Someone
said each process manages its own pool yet apparently this setup is
unacceptable for multithreaded db access.

thanks

Show quote

"Miha Markic [MVP C#]" wrote:
> DataAdapter, DataTable etc. are not thread safe.
> Plus, you have to make sure that you don't use same connection instance when
> two threads require it.