c# - Schema Lock issue when using ITable.AddField via ArcObjects

During a process I am running, I sometimes need to create a field that is missing in an attribute table. Unfortunately, the program is complaining that the table I am adding the field to has a schema lock from the program itself. So I attempted to add the ISchemaLock method for granting an exclusive lock and I now get the HRESULT error 0x8004022D when attempting to change the lock. Here is what the code looks like.

private void DoWork()
{
        IWorkspace workspace = getWorkspacefromPath(workspacepath);
        IFeatureWorkspace fWorkspace = (IFeatureWorkspace)workspace;
        IFeatureClass fc = fWorkspace.OpenFeatureClass(targetfile);
        if (fc == null)
        {
            MessageBox.Show("No feature class found.", "Error.");
            return;
        }

        ITable table = (ITable)fc;
        int index = table.FindField("PSTATE");
        if (index == -1)
        {
            ISchemaLock schemaLock = (ISchemaLock)table;
            settesttext("No PSTATE field found. Adding field now.");
            try
            {

                schemaLock.ChangeSchemaLock(esriSchemaLock.esriExclusiveSchemaLock);

                table.AddField(fielddata());

            }
            catch (Exception error)
            {
                MessageBox.Show("Field creation error. Closing process." + "\n " + error.Message);
                return;

            }
            finally

            {
                schemaLock.ChangeSchemaLock(esriSchemaLock.esriSharedSchemaLock);
            }
            settesttext("Field creation complete");
            index = table.FindField("PSTATE");
}

How should I go about adding the field to avoid getting a schema lock problem?

Answer

It appears that the lock was due to the IFeatureWorkspace maintaining a reference to the file GDB I was using.

Adding...

        fWorkspace = null;
        GC.Collect();

after creating the IFeatureClass instance did the trick. Thanks @blah238 for making me consider the workspace.