OgrProvider - Stability (Managed Wrappers)

[pielera]

Quote:

Ticket 415: Replace refcounting in OgrConnection by a better scheme involving overload of AddRef and Release. The code was written before AddRef and Release were virtual, so it had to use some hacks to do its job, and they are no longer necessary. It also *should* fix crashes during garbage collection when the provider is used via the managed wrappers (but this is just a guess).

Well... It doesn't:

Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at OSGeo.FDO.Connections.IConnectionImp.ReleaseUnmanagedObject()
   at OSGeo.FDO.Runtime.Disposable.Dispose()
   at ConsoleApplication1.Program.Main(String[] args) in D:\SOURCE\FDO_TEST\
ConsoleApplication1\Program.cs:line 30

Here the code to reproduce:

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                using (OSGeo.FDO.IProviderRegistry mRegistry = OSGeo.FDO.ClientServices.FeatureAccessManager.GetProviderRegistry())
                {
                    using (OSGeo.FDO.IConnectionManager mgr = OSGeo.FDO.ClientServices.FeatureAccessManager.GetConnectionManager())
                    {
                        using (OSGeo.FDO.ClientServices.ProviderCollection col = mRegistry.GetProviders())
                        {
                            for (int k = 0; k < 10; k++)
                            {
                                using (OSGeo.FDO.Connections.IConnection connection = mgr.CreateConnection("OSGeo.OGR.3.4"))
                                {
                                    using (OSGeo.FDO.Connections.IConnectionInfo connInfo = connection.ConnectionInfo)
                                    {
                                        using (OSGeo.FDO.Connections.IConnectionPropertyDictionary connPropDict = connInfo.ConnectionProperties)
                                        {
                                            List<string> lst = new List<string>(connPropDict.PropertyNames);
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
                Console.WriteLine(e.StackTrace);
            }
            Console.WriteLine("Finished");
            Console.ReadKey();
        }
    }
}

I wasted endless hours on this problem but was unable to fix it. I ended up removing the "delete this;" from the OgrConnection::Dispose method for the time being. So I can, at least, continue my project and further tests. And I'm well aware that this change results in a memory leak.

Here are my findings about this problem so far:

• OgrConnection::m_refCount is not initialized anywhere in the current code
• The crash only occurs with the OgrProvider release build (the debug build runs smoothly)
• It crashes when multiple different WrapperClasses have a reference to the OgrConnection object (e.g. IConnection and IConnectionInfo)

I really hope someone is able to fix this and so a stable FDO 3.4.0 can be released.

PS: As a last resort the OgrConnection can be split in multiple classes like the other providers if the refcounting-thingie is the problem. IMHO the refcounting part looks perfectly fine except for the refcount-initialization... but something is definitely wrong.

[traianstanev]

I set the refcount to 1 in the constructor, like it should have been. Hopefully this fixes the problem.

[pielera]

No. I tried that already and it doesn't change anything. Sorry, if i wasn't clear about that. I only pointed that out for the sake of completeness. The problem still exists.

[pielera]

I built a new version of fdo from trunk and surprise... It works. So does the current FDO 3.4 build.

I really don't know why this didn't work when i tried the same fix. Sorry. Consider it fixed now.