On Aug 24, 2012, at 9:15 AM, James Lavery <[email protected]> wrote:
> What we've found is that as soon as a GC_EXPLICIT is triggered, we're getting
> "Object reference not set to an instance of an object" errors and the system
> crashes.
You mention GC_EXPLICIT, then show code that's calling Close(). I'm slightly
confused. :-)
> The device log shows the following at the same time:
Is there any other output before the stack trace in the `adb logcat` output?
Perhaps something from Dalvik?
> 08-24 13:58:51.621 I/mono (12463): Stacktrace:
> 08-24 13:58:51.621 I/mono (12463):
> 08-24 13:58:51.621 I/mono (12463): at
> Android.Runtime.JNIEnv.CallVoidMethod (intptr,intptr)
> 08-24 13:58:51.621 I/mono (12463): at
> Com.Ianywhere.Ultralitejni12.IResultSetInvoker.Close ()
> 08-24 13:58:51.621 I/mono (12463): at
> Autoforms.Universal.Mobile.Droid.DAO.ResultSetConnection.Close ()
> 08-24 13:58:51.621 I/mono (12463): at
> Autoforms.Universal.Mobile.Droid.DAO.ResultSetConnection.Finalize ()
> 08-24 13:58:51.621 I/mono (12463): at (wrapper runtime-invoke)
> object.runtime_invoke_virtual_void__this__ (object,intptr,intptr,intptr)
This is very interesting; Close() is being called from Finalize().
Does your ResultSetConnection class provide a finalizer? Does it also subclass
Java.Lang.Object?
Java.Lang.Object subclasses MUST NOT provide a finalizer; override
Java.Lang.Object.Dispose(bool disposing) instead. Furthermore, as with the
normal IDisposable pattern, managed objects MUST NOT be referenced when
`disposing` is false, as those instances may have already been finalized:
partial class ResultSetConnection {
protected override void Dispose (bool disposing)
{
if (disposing) {
ResultSet.Close();
ResultSet.Dispose();
PreparedStatement.Close();
PreparedStatement.Dispose();
Connection.Release();
Connection.Dispose();
}
}
public void Close ()
{
if (Handle == IntPtr.Zero)
return;
base.Dispose ();
}
}
The above makes Close() a synonym for Dispose(), invalidating the instance
(which may or may not be appropriate for you, but is generally consistent with
the BCL, e.g. System.IO.Stream [0]).
- Jon
[0]
https://github.com/mono/mono/blob/master/mcs/class/corlib/System.IO/Stream.cs#L98
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