DeleteRealm wallways say file locked

[carbonete]

Goals

Delete local realm file and logout.

Expected Results

After dispose Instance, file is free to delete.

Actual Results

System.IO.IOException
HResult=0x80070020
Message=The process cannot access the file 'C:\Users\xxxxxxxxxxxxxxx.realm' because it is being used by another process.
Source=System.IO.FileSystem
StackTrace:
at System.IO.FileSystem.DeleteFile(String fullPath)
at System.IO.File.Delete(String path)
at Realms.Realm.DeleteRealm(RealmConfigurationBase configuration)

Steps to Reproduce

Run debugging and always receive this error. Instance is closed .

Code Sample

        public async void Logout()
        {
            if (RealmUser != null)
            {
                if (RealmSyncConfig != null)
                {
                    await RealmInstance.GetSession().WaitForUploadAsync();
                    RealmInstance.Dispose();
                    Realm.DeleteRealm(RealmSyncConfig);
                }
                await RealmUser.LogOutAsync();
                RealmSyncConfig = null;
            }
        }

Version of Realm and Tooling

• Flavor:
  • [ x] MongoDB Realm
  • Local Database only
• Client SDK Version: ? Realm .Net 10.2.0
• Client OS & Version: ? Windows 10 build 19041
  Microsoft Visual Studio Professional 2019
  Version 16.10.2
  VisualStudio.16.Release/16.10.2+31410.357
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  Version 4.8.04084

Installed Version: Professional

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[DominicFrei]

Hello @carbonete !

Thank you for that thorough report! :)

We've figured out that there are cases where this could happen.
For example the Realm still being in use (due to Sync) when trying to delete it. From my first look at your report it looks like that for me.

Good news:
We are in fact working on this right now already: #2401 (along with realm/realm-core#4768).

[carbonete]

Ok, thanks i will subscribe to follow.

[DominicFrei]

You can keep this issue open too if you want to. I did not want to push you into closing it just because we are aware of it. :)
It is a valid issue and the PR is not merged yet. @carbonete

[carbonete]

ok, thanks

[nirinchev]

I'm not sure the PR will resolve the issue - you'll get a more specific exception, but the underlying reason for the file being locked remains - the sync client is being shutdown asynchronously. When you call Dispose on the Realm instance, it will signal the sync client to shutdown but will not await the actual shutdown. While we will be exploring a convenience API in the future, as a stopgap, you can just retry the deletion waiting a few milliseconds between attempts - something like:

public static async Task DeleteWithRetries(RealmConfigurationBase config)
{
    for (var i = 0; i < 100; i++)
    {
        try
        {
            Realm.DeleteRealm(config);
            return;
        }
        catch
        {
            await Task.Delay(50);
        }
    }

    throw new Exception($"Failed to delete the Realm at {config.DatabasePath} after 100 attempts");
}

[carbonete]

@nirinchev Thanks for suggestion. But i test and result is the same in UWP app.

[nirinchev]

Is it possible you have the Realm instance open somewhere else? Dispose-ing of an instance will not close instances open on other threads - e.g.

var config = new SyncConfiguration(...);
var r1 = Realm.GetInstance(config);
var r2 = Realm.GetInstance(config);

r1.Dispose();

will keep r2 open, so you won't be able to delete the Realm file.

[carbonete]

Realm Instance is defined as static, and only one is used.

[DominicFrei]

Realm Instance is defined as static, and only one is used.

@carbonete Would you be able to show us this setup code as well?
Maybe you can extract that part into a small, stripped-down example app?

I've played a bit more with master and the changes I'm introducing with #2401 but I was not able to reproduce your exact problem on my side.

[DominicFrei]

Realm Instance is defined as static, and only one is used.

@carbonete Would you be able to show us this setup code as well?
Maybe you can extract that part into a small, stripped-down example app?

I've played a bit more with master and the changes I'm introducing with #2401 but I was not able to reproduce your exact problem on my side.

Ok, this reproduces the exact problem:
https://github.com/realm/realm-dotnet/tree/df/reproduction-for-2455

When I add a test (2b104da) I see:

System.IO.IOException : 
The process cannot access the file 
'C:\Users\xxxxxxxxxxxxxxxxxxxxxx.realm' because it is being used by another process.

When I then add a delay (5eeaa82) like @nirinchev mentioned in #2455 (comment) it fixes the problem.

Can you compare and try this against your code? @carbonete
And if it does not work, provide us with more details about where and how your code is different / showing us a more extensive example?