Running Dokan as Windows Service

[PedroVentura235]

Hello all!
So i am Using Dokan(great project BTW), where i am mounting a virtual drive based on files stored on a DB.
First i built a console application and got it working perfectly fine all operations.
Now, i would like to transfer it to a windows service, but i get some errors.
I am able to mount it sucessfully, but after a while i get this error:
Description: The process was terminated due to an unhandled exception.
Exception Info: System.AccessViolationException
at DokanNet.Native.NativeMethods.DokanCloseHandle(IntPtr)
at DokanNet.DokanHandle.ReleaseHandle()
at System.Runtime.InteropServices.SafeHandle.InternalFinalize()
at System.Runtime.InteropServices.SafeHandle.Dispose(Boolean)
at System.Runtime.InteropServices.SafeHandle.Finalize()
i didnt stop the service or something like that, was just exploring in the File explorer.
Has anybody worked with dokan and windows service, or has an alternative to windows service?
Thank you!

[Olof-Lagerkvist]

There are usually no issues running Dokan as a Windows service. What you see here is probably some kind of handle leak, or something encapsulated in a SafeHandle object that does not get disposed properly where it was used. Then, the SafeHandle object gets cleaned up at some point afterwards by garbage collector, but at that point the native handle that was encapsulated by the instance is no longer valid.

I suggest you go through all your relevant code paths in your implementation and check for places where you open files, database connections, network connections and similar and make sure that any objects used temporarily in such code paths are disposed before returning back to native Dokan library. Objects that are not temporary and should remain active throughout the lifetime of a mounted drive need to be stored as a field in your implementation object or some other global location and then disposed afterwards when your drive gets dismounted.

[Olof-Lagerkvist]

No, sorry, I missed an important part of your stack trace. What you are seeing is more probably your DokanInstance object with its properties getting cleaned up by the garbage collector before you actually wanted to dismount the file system. You need to keep your DokanInstance object alive throughout the lifetime of your mounted Dokan drive.

[PedroVentura235]

Hi, thanks for your input, this is what i think too as it works as expected as console application, any suggestion on how to keep it alive?
Currently i have it like this: and call it OnStart method

    private DokanInstance _dokanInstance;

var dokan = new Dokan(dokanLogger);
var dbfileSystem = new DokanFileSystem();
var dokanBuilder = new DokanInstanceBuilder(dokan)
.ConfigureOptions(options =>
{
options.MountPoint = $"{driveLetter}:\";
options.TimeOut = TimeSpan.FromMinutes(10); // Set a long timeout
options.SingleThread = false; // Use multiple threads
});

                // Create and mount the file system
                _dokanInstance = dokanBuilder.Build(dbfileSystem);

[Olof-Lagerkvist]

In which class is this? I would suggest that you add a service object using AddHostedService to your application host builder. There, you can keep your DokanInstance object as an instance field. There are obviously lots of other ways to do this too, but I personally like the AddHostedService concept because it makes it easy to run the whole thing as a normal console application too for testing out things etc.

[PedroVentura235]

I thought of that but i am using only .net framework and AddHostedService is on .net core i think.
This is a class dokan Service that i call in Program.cs from windows Service project

static class Program
{
///

/// The main entry point for the application.
///

static void Main()
{
ServiceBase[] ServicesToRun;
ServicesToRun = new ServiceBase[]
{
new DokanService()
};
ServiceBase.Run(ServicesToRun);
}
}

[Olof-Lagerkvist]

Okay I see. So, you have a DokanService class here that you instantiate. Is that where you keep your DokanInstance as a field? I would have expected that to work.

[PedroVentura235]

yes exactly.
this code is inside that class:
private DokanInstance _dokanInstance;
The code works, it mounts the drive fine.
however if i start exploring, or if i open the drive then close it, then open it again, i got the error i inserted on the first post.
That is what i am not understanding, only on exploring it breaks.
but on my console application(exactly the same implementation of IDokanOperations) i can move however i want it never breaks

[Olof-Lagerkvist]

There must be a reason why your DokanService instance and its fields get cleaned up by garbage collector. The object gets abandoned somehow.

[PedroVentura235]

Yap, will try to dig more.
thanks for your input!

[PedroVentura235]

i added some logs to the implementation of IDokanOperations and noticed that before the error the disk is Unmounted(it calls the Unmounted method) , but on my windows service, the stop method(or dispose) is not called

[Olof-Lagerkvist]

It could be that the reason it unmounts is connected to your objects getting cleaned up by garbage collector. Do you have some kind of logging in Main method right after ServiceBase.Run so that you know when Service Control Manager releases control of your application?

[PedroVentura235]

Added a log in here but in never logged:
static void Main()
{
ServiceBase[] ServicesToRun;
ServicesToRun = new ServiceBase[]
{
new DokanService()
};
ServiceBase.Run(ServicesToRun);
added log here
}
}

[Olof-Lagerkvist]

I must say this is a bit surprising. It looks like you do everything correctly, although it was quite a while since I last time implemented this in .NET Framework.

I guess you could try to add
GC.KeepAlive(ServicesToRun)
or possibly
GC.KeepAlive(ServicesToRun[0])
right after your call to ServiceBase.Run. This should ensure that the object is kept alive until at least that point.

[PedroVentura235]

still happens the same, if i am not exploring file explorer, on the logs, i also can see that sometimes, the dokan drive is unmounted without user interaction, and cant see why

[PedroVentura235]

So after some debug a lot of try error, was able to find a fix for now that works:

  private DokanInstance _dokanInstance;
var dokan = new Dokan(dokanLogger);
var dbfileSystem = new DokanFileSystem();
var dokanBuilder = new DokanInstanceBuilder(dokan)
.ConfigureOptions(options =>
{
options.MountPoint = $"{driveLetter}:\";
options.TimeOut = TimeSpan.FromMinutes(10); // Set a long timeout
options.SingleThread = false; // Use multiple threads
});

                // Create and mount the file system
                _dokanInstance = dokanBuilder.Build(dbfileSystem);

this is the previous code, and i was trying to mantain the _DokanINstance alive, but i have to make sure that dokan(new Dokan()) keeps alive as well!
For anyone in the future, keep dokan = new DOkan() alive so is not Garbage colelcted.
thank you @LTRData for your assist as well

[Olof-Lagerkvist]

Glad you found a solution!

Thinking more about this. I guess it would make sense for DokanInstance to also hold a reference to the Dokan object that created it (could be passed from DokanInstanceBuilder and similar concepts).
It would avoid situations like this and it make sense since it depends on that object in a way. If it gets disposed, the communication between native and managed code breaks anyway. @Liryna, do you agree or would this be a problematic design for some other reason?

[Liryna]

Yes, it totally make sense for the DokanInstance to keep a reference on Dokan since it needs it to stay alive! Do you wanna do the change ?

[Olof-Lagerkvist]

Yes sure. I can do that!

[Olof-Lagerkvist]

Made a commit with that change. I hope that helps in situations like this.
4394a73