Embedded server application has stopped working after exit

Question

I have an application that stores some data in firebird database. I'm using an embedded firebird server and EntityFramework and all works greatfully but when I close my app by x button on form I get a windows system message "application has stopped working" and I can't catch this exception. I have an UnhandledExceptionHandler in my app :

// Add handler for UI thread exceptions
Application.ThreadException += new ThreadExceptionEventHandler(UIThreadException);

// Force all WinForms errors to go through handler
Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException);

//This handler is for catching non-UI thread exceptions 
AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);

.....some other code..........

Application.Run(new MainForm());

But this kind of exception never been catched by it. So I went to windows event log and found there this xml-view of error-event :

- <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
- <System>
  <Provider Name="Application Error" /> 
  <EventID Qualifiers="0">1000</EventID> 
  <Level>2</Level> 
  <Task>100</Task> 
  <Keywords>0x80000000000000</Keywords> 
  <TimeCreated SystemTime="2017-03-14T23:06:25.000000000Z" /> 
  <EventRecordID>36077</EventRecordID> 
  <Channel>Application</Channel> 
  <Computer>MYPC</Computer> 
  <Security /> 
  </System>
- <EventData>
  <Data>MyApp.exe</Data> 
  <Data>1.0.0.0</Data> 
  <Data>58c7a3f0</Data> 
  <Data>fbintl.DLL</Data> 
  <Data>2.5.5.26952</Data> 
  <Data>5644432f</Data> 
  <Data>c0000005</Data> 
  <Data>00004e9c</Data> 
  <Data>1d64</Data> 
  <Data>01d29d1797fb7f0d</Data> 
  <Data>G:\Programming\WorkSpace\C#\MyApp\bin\x86\Debug\MyApp.exe</Data>
  <Data>G:\Programming\WorkSpace\C#\MyApp\bin\x86\Debug\FireBirdEmbeddedServer\intl\fbintl.DLL</Data> 
 <Data>d84a6ca6-090a-11e7-8151-005056c00008</Data> 
 </EventData>
 </Event>

As you see something went wrong with fbintl.DLL when app has closed already. So how I can get more detailed description about this problem?

UPD I make an app more shorter to detect a reason of my problem - now ONLY this EF code runs before app close

 public async Task GetAutoAnswerTemplate()
    {           
       try
        {
          using (var db = new FirebirdDbContext(embeddedConnectionString)){
            //Async or sync methods doesn't affect to my problem
             AutoAnswerTemplate template = await dbContext.AutoAnswerTemplate.FirstOrDefaultAsync();
            return template?.AutoAnswer_body;
          }
        }
        catch (Exception ex)
        {
            throw new EmbeddedFbDataBaseTools.EmbeddedDbException(
                "Error while getting auto answer template" + "\r\n" +  ex.Message, ex);
        }
    }

Where FirebirdDbContext is :

public class FirebirdDbContext : DbContext
{

    public FirebirdDbContext(string connString)
        : base(new FbConnection(connString), true)
    {
        //* The Entity initializer is bugged with Firebird embedded: http://stackoverflow.com/q/20959450/2504010  so I didn't use default--->
        //  Database.SetInitializer<FirebirdDBContext>(new CreateDatabaseIfNotExists<FirebirdDBContext>());    
        Database.SetInitializer<FirebirdDbContext>(new MyCreateDatabaseIfNotExists());
    }

    public DbSet<AutoAnswerTemplate> AutoAnswerTemplate { get; set; }
    public DbSet<User> User { get; set; }


}

class MyCreateDatabaseIfNotExists : IDatabaseInitializer<FirebirdDbContext>
{
    public void InitializeDatabase(FirebirdDbContext context)
    {
        if (!context.Database.Exists())
        {
            context.Database.Create();
        }
    }
}

And connection params is

  public static string GetEmbeddeddefaultConnectionString()
    {
        FbConnectionStringBuilder builder = new FbConnectionStringBuilder
        {
            ServerType = FbServerType.Embedded,
            DataSource = "localhost",
            Port = 3050,
            Database = EmbeddedDbPath, //Path to embedded db
            ClientLibrary = EmbeddedServerDllPath,
            UserID = "SYSDBA",
            Password = "masterkey",
            Charset = "WIN1251",
            Dialect = 3,
            ConnectionLifeTime = 15,
            Pooling = true,
            MinPoolSize = 0,
            MaxPoolSize = 50
        };
        return builder.ToString();
    }

NEW UPDATE 25.04.2017

I made a simple app with firebird embedded db that demonstrates the error. U can find it here

The app creates a firebird embedded database and connects to it in background thread (Task TPL), and after work is done (_bgTask.Status == TaskStatus.RanToCompletion) u close the app and get the error.

Answer 1

In your connection string, you have specified a character set and enabled connection pooling:

FbConnectionStringBuilder builder = new FbConnectionStringBuilder
{
    …
    Charset = "WIN1251",
    …
    Pooling = true,
    …
};

The combination of these two settings appears to trigger the error; not in your own code, but in FirebirdSQL's. I have so far found three ways to resolve this issue. You can do either of these:

1. Call the static FbConnection.ClearAllPools() method right before your application terminates (and leave connection pooling enabled):

   private static void AppExit(object sender, EventArgs e)
   {
       …
       FbConnection.ClearAllPools();
   }
   

2. Disable connection pooling by setting Pooling = false.

3. Since the error is triggered in fbintl.dll, which appears to be dealing with character sets / internationalization, you can simply omit the Charset connection string parameter (though I do not know what consequences this would have).

The last two suggestions are workarounds. I would probably go with option #1 as it seems to be cleanest, allows you to keep connection pooling enabled (which is usually a good thing), and specify the charset you need.

Note also that you might only ever see the exception if you run your application with a debugger attached. In production, the exception might well stay silent and go completely unnoticed.

Answer 2

Your exception handling shoud work except in 2 cases, stack overflow exceptions and memory exceptions. In this cases the behaviour should be the behaviour you described (system message "application has stopped working").
About stack overflow exceptions, with EF happens quite often when you serialize entities (json, xml, ...) with lazy load enabled. Are you serializing entities during exit?

If this is not your case you could check other two things:

• do you ever detach the two event handlers?
• are you causing exceptions in the exception handler?

Answer 3

It was a little tricky to debug you code _prepareAppTask = new TaskFactory().StartNew causes a race condition from time to time which in turn causes the exception I described in my original post.

Also it is not obvious that you throw and catch and exception behind the scenes when I tried to run DB code in main thread which caused unexpected behavior and made me thing the it solved the issue.

Other than that you I don't see any critical issues in your code which could lead to the error in question. It seems that either firebird itself or EF provider causes the issue on application shutdown. It has nothing to do with sync or async code - nothing like that. I was able to reproduce it simply running the console app.

App crashes on exit with Faulting module name: fbintl.DLL only if DB connection was created and DB was accessed by code. The answer to Faulting module what does this mean and why does this happen? makes me think that the issue is either with firebase or with EF provider.

Have you tried other ways to connect to firebase?

And if you only need to get rid of that nasty exception here is a hack that worked for me:

private static void AppExit(object sender, EventArgs e)
{
    ...
    // To ensure pending DB operations are processed. Not sure that's needed.
    int timeout = 1000;
    Thread.Sleep(timeout);
    Process.GetCurrentProcess().Kill();
}

Killing the process right before it exits prevents the error to show up.