It would be difficult to consider all the ramifications of doing this because you can t necessarily predict the resulting behavior of the application that currently has the file locked.

Is there some other way to do this? For example do you have to overwrite the file right away, or can you have some external process that continually tries to overwrite the file every few minutes until it succeeds?

I faced the same problem. So far I know, the only way to do that, is using the Win32API:

[DllImport("Netapi32.dll", SetLastError=true, CharSet = CharSet.Unicode)]
public static extern int NetFileClose(string servername, int id);

I made a short attempt to realize this and I can just enum the files right, but in my code - I had just a look into it - the code to close a file is set to be a comment. If you would give this a try, I can you sent a library [wrapper around NetFileXXX] and a short demo, but, as I said: I never closed a file. But this is possibly a short way to that.

I do not know, how to interchange file on stackoverflow now :-( ?!?

br--mabra

You can use code that you supply the full file path to, and it will return a List<Processes> of anything locking that file:

using System.Runtime.InteropServices;
using System.Diagnostics;

static public class FileUtil
{
    [StructLayout(LayoutKind.Sequential)]
    struct RM_UNIQUE_PROCESS
    {
        public int dwProcessId;
        public System.Runtime.InteropServices.ComTypes.FILETIME ProcessStartTime;
    }

    const int RmRebootReasonNone = 0;
    const int CCH_RM_MAX_APP_NAME = 255;
    const int CCH_RM_MAX_SVC_NAME = 63;

    enum RM_APP_TYPE
    {
        RmUnknownApp = 0,
        RmMainWindow = 1,
        RmOtherWindow = 2,
        RmService = 3,
        RmExplorer = 4,
        RmConsole = 5,
        RmCritical = 1000
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    struct RM_PROCESS_INFO
    {
        public RM_UNIQUE_PROCESS Process;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_APP_NAME + 1)]
        public string strAppName;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_SVC_NAME + 1)]
        public string strServiceShortName;

        public RM_APP_TYPE ApplicationType;
        public uint AppStatus;
        public uint TSSessionId;
        [MarshalAs(UnmanagedType.Bool)]
        public bool bRestartable;
    }

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    static extern int RmRegisterResources(uint pSessionHandle,
                                          UInt32 nFiles,
                                          string[] rgsFilenames,
                                          UInt32 nApplications,
                                          [In] RM_UNIQUE_PROCESS[] rgApplications,
                                          UInt32 nServices,
                                          string[] rgsServiceNames);

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Auto)]
    static extern int RmStartSession(out uint pSessionHandle, int dwSessionFlags, string strSessionKey);

    [DllImport("rstrtmgr.dll")]
    static extern int RmEndSession(uint pSessionHandle);

    [DllImport("rstrtmgr.dll")]
    static extern int RmGetList(uint dwSessionHandle,
                                out uint pnProcInfoNeeded,
                                ref uint pnProcInfo,
                                [In, Out] RM_PROCESS_INFO[] rgAffectedApps,
                                ref uint lpdwRebootReasons);

    /// <summary>
    /// Find out what process(es) have a lock on the specified file.
    /// </summary>
    /// <param name="path">Path of the file.</param>
    /// <returns>Processes locking the file</returns>
    /// <remarks>See also:
    /// http://msdn.microsoft.com/en-us/library/windows/desktop/aa373661(v=vs.85).aspx
    /// http://wyupdate.googlecode.com/svn-history/r401/trunk/frmFilesInUse.cs (no copyright in code at time of viewing)
    /// 
    /// </remarks>
    static public List<Process> WhoIsLocking(string path)
    {
        uint handle;
        string key = Guid.NewGuid().ToString();
        List<Process> processes = new List<Process>();

        int res = RmStartSession(out handle, 0, key);
        if (res != 0) throw new Exception("Could not begin restart session.  Unable to determine file locker.");

        try
        {
            const int ERROR_MORE_DATA = 234;
            uint pnProcInfoNeeded = 0,
                 pnProcInfo = 0,
                 lpdwRebootReasons = RmRebootReasonNone;

            string[] resources = new string[] { path }; // Just checking on one resource.

            res = RmRegisterResources(handle, (uint)resources.Length, resources, 0, null, 0, null);

            if (res != 0) throw new Exception("Could not register resource.");                                    

            //Note: there s a race condition here -- the first call to RmGetList() returns
            //      the total number of process. However, when we call RmGetList() again to get
            //      the actual processes this number may have increased.
            res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, null, ref lpdwRebootReasons);

            if (res == ERROR_MORE_DATA)
            {
                // Create an array to store the process results
                RM_PROCESS_INFO[] processInfo = new RM_PROCESS_INFO[pnProcInfoNeeded];
                pnProcInfo = pnProcInfoNeeded;

                // Get the list
                res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, processInfo, ref lpdwRebootReasons);
                if (res == 0)
                {
                    processes = new List<Process>((int)pnProcInfo);

                    // Enumerate all of the results and add them to the 
                    // list to be returned
                    for (int i = 0; i < pnProcInfo; i++)
                    {
                        try
                        {
                            processes.Add(Process.GetProcessById(processInfo[i].Process.dwProcessId));
                        }
                        // catch the error -- in case the process is no longer running
                        catch (ArgumentException) { }
                    }
                }
                else throw new Exception("Could not list processes locking resource.");                    
            }
            else if (res != 0) throw new Exception("Could not list processes locking resource. Failed to get size of result.");                    
        }
        finally
        {
            RmEndSession(handle);
        }

        return processes;
    }
}

Then, iterate the list of processes and close them:

    string[] files = Directory.GetFiles(target_dir);
    List<Process> lstProcs = new List<Process>();

    foreach (string file in files)
    {
        lstProcs = ProcessHandler.WhoIsLocking(file);
        if (lstProcs.Count > 0) // deal with the file lock
        {
            foreach (Process p in lstProcs)
            {
                if (p.MachineName == ".")
                    ProcessHandler.localProcessKill(p.ProcessName);
                else
                    ProcessHandler.remoteProcessKill(p.MachineName, txtUserName.Text, txtPassword.Password, p.ProcessName);
            }
        }
    }

And depending on if the file is on the local computer:

public static void localProcessKill(string processName)
{
    foreach (Process p in Process.GetProcessesByName(processName))
    {
        p.Kill();
    }
}

or a network computer:

public static void remoteProcessKill(string computerName, string fullUserName, string pword, string processName)
{
    var connectoptions = new ConnectionOptions();
    connectoptions.Username = fullUserName;  // @"YourDomainNameUserName";
    connectoptions.Password = pword;

    ManagementScope scope = new ManagementScope(@"\" + computerName + @"
ootcimv2", connectoptions);

    // WMI query
    var query = new SelectQuery("select * from Win32_process where name =  " + processName + " ");

    using (var searcher = new ManagementObjectSearcher(scope, query))
    {
        foreach (ManagementObject process in searcher.Get()) 
        {
            process.InvokeMethod("Terminate", null);
            process.Dispose();
        }
    }
}

References:
How do I find out which process is locking a file using .NET?

Delete a directory where someone has opened a file