Way to get USB hard drives via unmanaged code

Question

Hello,
I was using HwndSource to get notification when usb drives change, and WMI to get current USB devices, on a background thread.  However, I get this exception:
The application called an interface that was marshalled for a different thread.  ---> System.Runtime.InteropServices.COMException (0x8001010E): The application called an interface that was marshalled for a different thread. (Exception from HRESULT: 0x8001010E (RPC_E_WRONG_THREAD))

I can't use System.IO.DriveInfo.GetDrives() because USB hard drives types are FIXED and not removable, only usb key/thumbdrives are removabble.

Are there unmanaged functions I can use via p/invoke to get all the usb drives?

Here is most of my existing code:

var handle = new WindowInteropHelper(window).Handle;

            this.hwndSource = HwndSource.FromHwnd(handle);
            this.wndProc = new HwndSourceHook(this.HwndMessage);
            this.hwndSource.AddHook(this.wndProc);


        private IntPtr HwndMessage(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            // Handle whatever Win32 message it is we feel like handling
            if (msg == NativeMethods.WM_DEVICECHANGE)
            {
                if (wParam.ToInt32() == NativeMethods.DBT_DEVICEARRIVAL || wParam.ToInt32() == NativeMethods.DBT_DEVICEREMOVECOMPLETE)
                {
                    OnUsbDeviceChange();
                }
            }
            return IntPtr.Zero;
        }

        private void OnUsbDeviceChange()
        {
            IList<ManagementObject> usbDrives = new List<ManagementObject>();

            try
            {
                ManagementObjectCollection drives = new ManagementObjectSearcher("SELECT Caption, DeviceID FROM Win32_DiskDrive WHERE InterfaceType='USB'").Get();

                if (drives.Count > 0)
                {
                    // browse all USB WMI physical disks
                    foreach (ManagementObject drive in drives)
                    {
                        // browse all USB WMI physical disks
                        foreach (ManagementObject partition in new ManagementObjectSearcher( "ASSOCIATORS OF {Win32_DiskDrive.DeviceID='" + drive["DeviceID"]
                                    + "'} WHERE AssocClass = Win32_DiskDriveToDiskPartition").Get())
                        {
                            // browse all USB WMI physical disks
                            foreach (ManagementObject disk in new ManagementObjectSearcher("ASSOCIATORS OF {Win32_DiskPartition.DeviceID='"
                                    + partition["DeviceID"] + "'} WHERE AssocClass = Win32_LogicalDiskToPartition").Get())
                            {
                                usbDrives.Add(disk);
                            }
                        }
                    }
            }
            }
            catch (Exception)
            {
                throw;
            }

}

thanks,

dan

Answer 1

Hmm, this is perhaps not relevant, but maybe worth a try; Is the window you are capturing the messages for a form ? If so, when you receive a message what does the .InvokeRequired property of the form return ? It seems unlikely, but if it is returning true, then you might want to try running your OnUsbDeviceChange method via a delegate and the form.Invoke method to see if it avoids the exception about being on the wrong thread.

Alternatively, could you run that code on a background thread anyway.. i.e if you change the window hook to call OnUsbDeviceChange via the thread pool or a new thread, are those threads then able to access the WMI stuff without the thread error ?

Answer 2

COM is single threaded. Therefore, make sure that you are handling the code in the thread that created the COM object.

To answer your question:

"Are there unmanaged functions I can use via p/invoke to get all the usb drives?"

No, the point of Platform Invoke is to call unmanaged functions.

---

Geert van Horrik - CatenaLogic
Visit my blog: http://blog.catenalogic.com

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Answer 3

thanks, I just dispatched getting the updated list on the window object, and it seems to work OK....

                _window.Dispatcher.BeginInvoke(DispatcherPriority.Background, 
                    (ThreadStart) ( () =>
                    {
                        IList<IUsbDevice> devices = GetUsbPeripheralDrives();
                        tempHandler(this, new GenericEventArgs<IList<IUsbDevice>>(devices));
                    })
                    );

Answer 4

yeah i know the point of platform invoke calls, i was asking if there are unmanaged functions I can use to get usb drives instead of using dealing with COM and WMI.

Answer 5

So effectively you used invoke like I suggested (just via a different pattern) ?

Answer 6

I had the same problem while trying to get USB thumb drive information when one is inserted.  First I got the ManagementException, rewrote the software, and then got a COMException.  In my Program.cs, on the Main method, I changed the [STAThread] to [MTAThread], reran the app and it worked.  Perhaps this will work for you too.