C#

protected override bool ShowWithoutActivation
    {
    get { return true; }
    }

///...code code code and more code in your worker thread

string nextText = "qwe"; 
this.Invoke( (MethodInvoker)delegate {
    oneLabel.Text = nextText; // runs on main thread
}
);

///...and goes more code in your worker thread

class DatabaseUpdater {
 event EventHandler<UpdateEventArgs> Update;

 void ThreadMethod() {
  while(true){ 
   // ... check the db
   if(thereWasAnUpdate && Update != null){
    Update(this, new UpdateEventArgs(updatedTable, key, Value);
    // or whatever you want to be in your UpdateEventArgs
   }
  }
 }
}

class MainForm {
 List<DatabaseUpdater> updaters;
 MainForm(){
  // ...
  foreach(DatabaseUpdater updater in updaters)
   updater.Update += DatabaseUpdated;
 }

 void DatabaseUpdated(object sender, UpdateEventArgs e){
  this.Invoke((MethodInvoker) delegate { myTextBox.Text += e.UpdatedTable + "\n"; });
 }
}