C#•3y ago

Multiple Users Concurrency Issue? EF6

It's a backend API with EF6 and frontend React/js coupled together (can't run the API separately). When multiple users try to upload a file at the same time, or run the main loop to perform calculations, the app crashes. The error message from the log is:

System.InvalidOperationException: Unexpected connection state. When using a wrapping provider ensure that the StateChange event is implemented on the wrapped DbConnection.

System.InvalidOperationException: Unexpected connection state. When using a wrapping provider ensure that the StateChange event is implemented on the wrapped DbConnection.

There was also a duplicate key error, but that must stem from the concurrency issues we're seeing.

The site works as intended even if users upload and run the main loop seconds apart, just not at the same time.

Can anyone pinpoint what this error actually means and the resolution? I've spent several hours reading, and it seems like it comes down to improper db context usage, but we instantiate a db context whenever we need it. I found an article that says this (see attached). I think we're doing that, but I don't know how to confirm.

NattyOP•1/20/23, 5:16 PM

None of the db contexts are wrapped in a

using

using

statement either. There is also no direct being called. It's all being handled by the GC, would this be any issue?

NattyOP•1/20/23, 5:18 PM

There's also endless methods being used nearly everywhere, that I would imagine are manipulating state as well....

D.Mentia•1/20/23, 5:29 PM

Old contexts not being disposed sounds like it could be it. Eventually it'd just run out of connections on the db

NNatty None of the db contexts are wrapped in a `using` statement either. There is also...

RDasher•1/20/23, 5:48 PM

I've had this issue before, and it was because of Undisposed DbConnections
Always be sure to dispose of DbConnections and IDisposables that have fufilled their purpose (or use the

using

using

statement)

RDasher•1/20/23, 5:50 PM

And, are you sure you are running your backend API multi-threaded? Using something like the class?

RRDasher I've had this issue before, and it was because of Undisposed DbConnections Alway...

NattyOP•1/20/23, 5:54 PM

So you think every time a _db context is being used, do it within a

using

using

? Right now, we're just directly instantiating at the top of the controller.

RRDasher And, are you sure you are running your backend API multi-threaded? Using somethi...

NattyOP•1/20/23, 5:55 PM

To be honest, I don't know, I wasn't sure how to confirm if it was single or multi. Not using Semaphore.

RRDasher And, are you sure you are running your backend API multi-threaded? Using somethi...

NattyOP•1/20/23, 6:00 PM

So if we're not using any out of the ordinary things, then the api is single threaded?

RDasher•1/20/23, 6:01 PM

Yes, I would say from the sounds of, it sounds like a single threaded application

NNatty So you think every time a _db context is being used, do it within a `using`? Rig...

RDasher•1/20/23, 6:01 PM

Can you share an example if possible?

RRDasher Can you share an example if possible?

NattyOP•1/20/23, 6:02 PM

Ok, I'd imagine that's correct. It's really just a poorly structured EF6 Api... Hm, sure, let me share the Upload Controller, which the app was failing here when multiple users were trying to upload.

NattyOP•1/20/23, 6:03 PM

https://hastepaste.com/view/nlX1D

RDasher•1/20/23, 6:03 PM

There is nothing wrong with single threaded applications, they are much easier to work with

RDasher•1/20/23, 6:03 PM

Lemme check

NattyOP•1/20/23, 6:03 PM

Again, very poorly structured.

RDasher•1/20/23, 6:04 PM

What's happening in

RRDasher Lemme check

NattyOP•1/20/23, 6:04 PM

Can you tell me too, is the Dispose method at the bottom actually doing anything? Some other dev put it there, but that's the only implementation of it, and it's never being called, etc.

RRDasher What's happening in `Context()`

NattyOP•1/20/23, 6:04 PM

Meaning?

NattyOP•1/20/23, 6:04 PM

It's just the db context.

RDasher•1/20/23, 6:05 PM

Oh, I see

NattyOP•1/20/23, 6:05 PM

Usually in .net core it's through DI with the service, but not in EF6 and this project was near "done" by the time i started, so didnt implement Automapper, etc

RDasher•1/20/23, 6:06 PM

You mean, a class like this?

NattyOP•1/20/23, 6:06 PM

I am aware too that this is "fake async" methods, I am having the one dev fix that at the very least, awaiting and making all possible methods async.

RRDasher You mean, a class like this? ```cs public partial class SchoolDBEntities : DbCon...

NattyOP•1/20/23, 6:06 PM

Yes, correct!

NattyOP•1/20/23, 6:06 PM

Let me grab a copy.. one sec...

RDasher•1/20/23, 6:07 PM

The dispose is not doing anything if it is not being invoked

NattyOP•1/20/23, 6:07 PM

https://hastepaste.com/view/v5NBJl7M

RDasher•1/20/23, 6:08 PM

Actually, no, I might be wrong about this

RDasher•1/20/23, 6:08 PM

I don't think you should dispose of it

NattyOP•1/20/23, 6:08 PM

yeah since it's overrirding, i wasnt sure if it is still in fact doing something?

NattyOP•1/20/23, 6:09 PM

even though there's no direct call.

RDasher•1/20/23, 6:09 PM

You approach is much more rudimentary than ours

RDasher•1/20/23, 6:09 PM

Okay, yeah I've figured it

RDasher•1/20/23, 6:09 PM

DBContext will dispose of itself fine

RDasher•1/20/23, 6:10 PM

I was wrong about that bit

RDasher•1/20/23, 6:10 PM

So you don't need to manually dispose, nor do you need to use using statements

NattyOP•1/20/23, 6:10 PM

Yeah, through the GC, regardless if using

using

using

or not.

RDasher•1/20/23, 6:10 PM

What you do need to do, is don't initialize on top of the controller

NattyOP•1/20/23, 6:10 PM

However, the timing of it could differ, and i'm not sure if that matters, when there's multiple users.

NNatty Yeah, through the GC, regardless if using `using` or not.

RDasher•1/20/23, 6:11 PM

No, not even through the GC, DBContext manages it's own lifetime

RDasher•1/20/23, 6:11 PM

What you should do, is move the initialization of

db

db

into the methods

RRDasher What you should do, is move the initialization of `db` into the methods

NattyOP•1/20/23, 6:12 PM

Ok, so having it at the top means it's being shared rather than one instance per request?

RDasher•1/20/23, 6:14 PM

Example:

Becomes

NattyOP•1/20/23, 6:14 PM

Gotcha yea

NNatty Ok, so having it at the top means it's being shared rather than one instance per...

RDasher•1/20/23, 6:14 PM

That, and what happens is likely that that becomes cached

NattyOP•1/20/23, 6:15 PM

I did read about that too, and the cache becomes stale, but i couldnt really inquire further about when/how/what that all meant lol

RDasher•1/20/23, 6:15 PM

Hopefully this solves your issue, good luck

NattyOP•1/20/23, 6:15 PM

Thank you!