C# CopyFileEx - ProgressRoutine : do we really need to close the destination file handle while progress?

Question

I tried to close the handle in the ProgressRoutine when the transferred bytes size is greater than or equal to total file length. but the whole operation rarely throws System.IO.IOException : The Handle is invalid.

bool result = CopyFileEx(source, destination, new CopyProgressRoutine(CopyProgressHandler), IntPtr.Zero, ref IsCancelled, copyFileFlags);
if (!result)
{
    //when ever we get the result as false it means some error occured so get the last win 32 error.
    throw new Win32Exception(Marshal.GetLastWin32Error());
}

here is the CopyProgressHandler method

private CopyProgressResult CopyProgressHandler(long total, long transferred, long streamSize, long streamByteTrans, uint dwStreamNumber,
                                                CopyProgressCallbackReason reason, IntPtr hSourceFile, IntPtr hDestinationFile, IntPtr lpData)
{
    //when a chunk is finished call the progress changed.
    if (reason == CopyProgressCallbackReason.CALLBACK_CHUNK_FINISHED)
    {
        OnProgressChanged((transferred / (double)total) * 100.0);
    }

    //transfer completed
    if (transferred >= total)
    {
        if (CloseHandle(hDestinationFile)) // here is that valid!! ?
        {
            //if file is read only, remove read-only attribute(case to handle CD drive import)
            FileAttributes attr = File.GetAttributes(destinationFilePath);
            if ((attr & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
            {
                attr =  attr & ~FileAttributes.ReadOnly;
                File.SetAttributes(destinationFilePath, attr);
            }

            OnCompleted(CopyCompletedType.Succeeded, null);
        }
        else
        {
            OnCompleted(CopyCompletedType.Exception,
                new System.IO.IOException("Unable to close the file handle"));
        }
    }

    return CopyProgressResult.PROGRESS_CONTINUE;
}
[System.Runtime.InteropServices.DllImport("Kernel32")]
private extern static Boolean CloseHandle(IntPtr handle);

[DllImport("kernel32.dll", SetLastError = true, CharSet = CharSet.Auto)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool CopyFileEx(string lpExistingFileName, string lpNewFileName, CopyProgressRoutine lpProgressRoutine, IntPtr lpData, ref Int32 pbCancel, CopyFileFlags dwCopyFlags);

private delegate CopyProgressResult CopyProgressRoutine(long TotalFileSize, long TotalBytesTransferred, long StreamSize, long StreamBytesTransferred, uint dwStreamNumber, CopyProgressCallbackReason dwCallbackReason,
                                                IntPtr hSourceFile, IntPtr hDestinationFile, IntPtr lpData);

private enum CopyProgressResult : uint
{
    PROGRESS_CONTINUE = 0,
    PROGRESS_CANCEL = 1,
    PROGRESS_STOP = 2,
    PROGRESS_QUIET = 3
}

private enum CopyProgressCallbackReason : uint
{
    CALLBACK_CHUNK_FINISHED = 0x00000000,
    CALLBACK_STREAM_SWITCH = 0x00000001
}

[Flags]
private enum CopyFileFlags : uint
{
    COPY_FILE_FAIL_IF_EXISTS = 0x00000001,
    COPY_FILE_NO_BUFFERING = 0x00001000,
    COPY_FILE_RESTARTABLE = 0x00000002,
    COPY_FILE_OPEN_SOURCE_FOR_WRITE = 0x00000004,
    COPY_FILE_ALLOW_DECRYPTED_DESTINATION = 0x00000008
}

if that is valid, why the error ? Do we really need to close the handle or it will be closed by CopyFileEx ? but if I removed the code CloseHandle i never get this exception. But the destination file is used by another operation after this copy, Thats why I equipped this.!

Please help to avoid the System.IO.IOException : The handle is invalid error.

Answer 1

You must not close the handles. The handles are owned by CopyFileEx and it closes them. Remove the calls to CloseHandle.