FileHelper.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Runtime.InteropServices;

namespace FileLockingDemo
{
    public class FileHelper
    {
         [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;
        }
        
        public static bool IsFileLocked(FileInfo file, out List<Process> whoIsLocking)
        {
            whoIsLocking = null;
            try
            {
                using (var stream = file.Open(FileMode.Open, FileAccess.Read, FileShare.None))
                {
                    stream.Close();
                }
            }
            catch (IOException)
            {
                whoIsLocking = WhoIsLocking(file.FullName);
                return true;
            }

            //file is not locked
            return false;
        } 
    }
}