How to avoid RaceOnRCW when calling the ComboBox Clear function using Invoke - multithreading

Question

I am working on a UART terminal program like TeraTerm. I am making my own terminal program since I need some features that I can't find in other terminal programs.
My terminal program can open several terminal windows that each display the output from a chosen COM port. Each terminal window runs in its own thread.
I have overridden the terminal window form's WndProc function to catch device changed events since I want to update a ComboBox's items with the current PC's available COM ports. This is done to keep the list of COM ports up to date if the user is plugging in a USB COM port device.
My WndProc looks as follows:
protected override void WndProc(ref Message m)
{
switch(m.Msg)
{
case WM_DEVICECHANGE:
GetAvailableCOMPorts();
COMPortsComboBox.Invoke(UpdateCOMPortsComboBoxDelegate);
break;
}
base.WndProc(ref m);
}
The UpdateCOMPortsComboBoxDelegate is the function updating the items in the ComboBox when a device change occurs. It does not matter if the device wa not a COM device. I do not check to keep it simple.
The UpdateCOMPortsComboBox function pointed to by the delegate looks as follows:
private void UpdateCOMPortsComboBox()
{
bool State = COMPortsComboBox.Enabled;
COMPortsComboBox.Enabled = false;
COMPortsComboBox.Items.Clear();
COMPortsComboBox.Enabled = State;
// Then add the new list of COM ports
for(int i = 0; i < AvailableSerialPorts.Length; i++)
{
COMPortsComboBox.Items.Add(AvailableSerialPorts[i]);
}
}
My problems is that I sometimes get a RaceOnRCW at the Clear() method call even though I have used Invoke to make sure it is called on the thread running the controls message loop.
What is going on?
How do I prevent this from happening?
Or maybe how can I figure out if a control is in use on another thread? And then perhaps wait for the other thread to finish.
Is there perhaps a better way to update the ComboBox items with a new list when the device change event occurs?
The call stack looks as follows when it happens:
mscorlib.dll!System.__ComObject.ReleaseSelf() + 0x5 bytes
mscorlib.dll!System.Runtime.InteropServices.Marshal.ReleaseComObject(object o) + 0x9a bytes
System.Windows.Forms.dll!System.Windows.Forms.StringSource.ReleaseAutoComplete() + 0x11 bytes
System.Windows.Forms.dll!System.Windows.Forms.ComboBox.OnHandleDestroyed(System.EventArgs e) + 0x85 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.WmDestroy(ref System.Windows.Forms.Message m) + 0x46 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.WndProc(ref System.Windows.Forms.Message m) + 0x44d bytes
System.Windows.Forms.dll!System.Windows.Forms.ComboBox.WndProc(ref System.Windows.Forms.Message m) + 0x882 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.OnMessage(ref System.Windows.Forms.Message m) + 0x13 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.WndProc(ref System.Windows.Forms.Message m) + 0x31 bytes
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DebuggableCallback(System.IntPtr hWnd, int msg, System.IntPtr wparam, System.IntPtr lparam) + 0x64 bytes
[Native to Managed Transition]
[Managed to Native Transition]
System.Windows.Forms.dll!System.Windows.Forms.UnsafeNativeMethods.DestroyWindow(System.Runtime.InteropServices.HandleRef hWnd) + 0x10 bytes
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DestroyHandle() + 0x89 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.DestroyHandle() + 0x157 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.RecreateHandleCore() + 0x16a bytes
System.Windows.Forms.dll!System.Windows.Forms.ComboBox.RecreateHandleCore() + 0x1a bytes
System.Windows.Forms.dll!System.Windows.Forms.ComboBox.SetAutoComplete(bool reset, bool recreate) + 0x105 bytes
System.Windows.Forms.dll!System.Windows.Forms.ComboBox.ObjectCollection.ClearInternal() + 0xa1 bytes
System.Windows.Forms.dll!System.Windows.Forms.ComboBox.ObjectCollection.Clear() + 0x17 bytes
> Echo.exe!Echo.Echo.UpdateCOMPortsComboBox() Line 231 + 0x1d bytes C#
[Native to Managed Transition]
mscorlib.dll!System.Delegate.DynamicInvokeImpl(object[] args) + 0x77 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbackDo(System.Windows.Forms.Control.ThreadMethodEntry tme) + 0xa7 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(object obj) + 0x90 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallback(System.Windows.Forms.Control.ThreadMethodEntry tme) + 0xa2 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbacks() + 0xda bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.MarshaledInvoke(System.Windows.Forms.Control caller, System.Delegate method, object[] args, bool synchronous) + 0x365 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.Invoke(System.Delegate method, object[] args) + 0x50 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.Invoke(System.Delegate method) + 0x7 bytes
Echo.exe!Echo.Echo.WndProc(ref System.Windows.Forms.Message m) Line 247 + 0x19 bytes C#
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.OnMessage(ref System.Windows.Forms.Message m) + 0x13 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.WndProc(ref System.Windows.Forms.Message m) + 0x31 bytes
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DebuggableCallback(System.IntPtr hWnd, int msg, System.IntPtr wparam, System.IntPtr lparam) + 0x64 bytes
[Native to Managed Transition]
[Managed to Native Transition]
System.Windows.Forms.dll!System.Windows.Forms.StringSource.Bind(System.Runtime.InteropServices.HandleRef edit, int options) + 0x46 bytes
System.Windows.Forms.dll!System.Windows.Forms.ComboBox.SetAutoComplete(bool reset, bool recreate) + 0x2f4 bytes
System.Windows.Forms.dll!System.Windows.Forms.ComboBox.ObjectCollection.Add(object item) + 0x55 bytes
Echo.exe!Echo.Echo.UpdateCOMPortsComboBox() Line 237 + 0x34 bytes C#
[Native to Managed Transition]
mscorlib.dll!System.Delegate.DynamicInvokeImpl(object[] args) + 0x77 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbackDo(System.Windows.Forms.Control.ThreadMethodEntry tme) + 0xa7 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(object obj) + 0x90 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallback(System.Windows.Forms.Control.ThreadMethodEntry tme) + 0xa2 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.InvokeMarshaledCallbacks() + 0xda bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.MarshaledInvoke(System.Windows.Forms.Control caller, System.Delegate method, object[] args, bool synchronous) + 0x365 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.Invoke(System.Delegate method, object[] args) + 0x50 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.Invoke(System.Delegate method) + 0x7 bytes
Echo.exe!Echo.Echo.WndProc(ref System.Windows.Forms.Message m) Line 247 + 0x19 bytes C#
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.OnMessage(ref System.Windows.Forms.Message m) + 0x13 bytes
System.Windows.Forms.dll!System.Windows.Forms.Control.ControlNativeWindow.WndProc(ref System.Windows.Forms.Message m) + 0x31 bytes
System.Windows.Forms.dll!System.Windows.Forms.NativeWindow.DebuggableCallback(System.IntPtr hWnd, int msg, System.IntPtr wparam, System.IntPtr lparam) + 0x64 bytes
[Native to Managed Transition]
[Managed to Native Transition]
System.Windows.Forms.dll!System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(System.IntPtr dwComponentID, int reason, int pvLoopData) + 0x1b8 bytes
System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(int reason, System.Windows.Forms.ApplicationContext context) + 0x16c bytes
System.Windows.Forms.dll!System.Windows.Forms.Application.ThreadContext.RunMessageLoop(int reason, System.Windows.Forms.ApplicationContext context) + 0x61 bytes
System.Windows.Forms.dll!System.Windows.Forms.Application.RunDialog(System.Windows.Forms.Form form) + 0x33 bytes
System.Windows.Forms.dll!System.Windows.Forms.Form.ShowDialog(System.Windows.Forms.IWin32Window owner) + 0x38f bytes
System.Windows.Forms.dll!System.Windows.Forms.Form.ShowDialog() + 0x7 bytes
Echo.exe!Echo.Program.NewEcho() Line 48 + 0xa bytes C#
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart_Context(object state) + 0x63 bytes
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool ignoreSyncCtx) + 0xb0 bytes
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x2c bytes
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart() + 0x44 bytes
[Native to Managed Transition]
I use the following code to create new terminal windows in a separate thread:
public static void CreateNewEchoThread()
{
//// Create a new thread
Thread EchoThread = new Thread(new ThreadStart(Program.NewEcho));
// Set thread parameters
EchoThread.IsBackground = true;
EchoThread.SetApartmentState(ApartmentState.STA);
//// Start the thread
EchoThread.Start();
// Increment the number of open Echo forms
Echo.NumberOfOpenWindows++;
}
[STAThread]
static void NewEcho()
{
// Create a new Echo form window and show it as a Dialog to prevent the thread from exiting immediately.
Echo NewEchoForm = new Echo();
NewEchoForm.ShowDialog();
}

Answer 1

I found a way to avoid the RaceOnRCW.
I replace the Clear call by a loop that removes each item one by one. Not the solution I like, but it seems to work.
I would still like to hear other ideas about how to do it, since it bothers me that I can't use the Clear function.
int NItems = COMPortsComboBox.Items.Count;
for(int i = 0; i < NItems; i++)
{
COMPortsComboBox.Items.RemoveAt(0);
}