Question

I am writing a directory scanner in .NET.

For each File/Dir I need the following info.

   class Info {         public bool IsDirectory;         public string Path;         public DateTime ModifiedDate;         public DateTime CreatedDate;     } 

I have this function:

      static List<Info> RecursiveMovieFolderScan(string path){          var info = new List<Info>();         var dirInfo = new DirectoryInfo(path);         foreach (var dir in dirInfo.GetDirectories()) {             info.Add(new Info() {                 IsDirectory = true,                 CreatedDate = dir.CreationTimeUtc,                 ModifiedDate = dir.LastWriteTimeUtc,                 Path = dir.FullName             });              info.AddRange(RecursiveMovieFolderScan(dir.FullName));         }          foreach (var file in dirInfo.GetFiles()) {             info.Add(new Info()             {                 IsDirectory = false,                 CreatedDate = file.CreationTimeUtc,                 ModifiedDate = file.LastWriteTimeUtc,                 Path = file.FullName             });         }          return info;      } 

Turns out this implementation is quite slow. Is there any way to speed this up? I’m thinking of hand coding this with FindFirstFileW but would like to avoid that if there is a built in way that is faster.

Answer 1

This implementation, which needs a bit of tweaking is 5-10X faster.

    static List<Info> RecursiveScan2(string directory) {         IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1);         WIN32_FIND_DATAW findData;         IntPtr findHandle = INVALID_HANDLE_VALUE;          var info = new List<Info>();         try {             findHandle = FindFirstFileW(directory + @'\*', out findData);             if (findHandle != INVALID_HANDLE_VALUE) {                  do {                     if (findData.cFileName == '.' || findData.cFileName == '..') continue;                      string fullpath = directory + (directory.EndsWith('\\') ? '' : '\\') + findData.cFileName;                      bool isDir = false;                      if ((findData.dwFileAttributes & FileAttributes.Directory) != 0) {                         isDir = true;                         info.AddRange(RecursiveScan2(fullpath));                     }                      info.Add(new Info()                     {                         CreatedDate = findData.ftCreationTime.ToDateTime(),                         ModifiedDate = findData.ftLastWriteTime.ToDateTime(),                         IsDirectory = isDir,                         Path = fullpath                     });                 }                 while (FindNextFile(findHandle, out findData));              }         } finally {             if (findHandle != INVALID_HANDLE_VALUE) FindClose(findHandle);         }         return info;     } 

extension method:

 public static class FILETIMEExtensions {         public static DateTime ToDateTime(this System.Runtime.InteropServices.ComTypes.FILETIME filetime ) {             long highBits = filetime.dwHighDateTime;             highBits = highBits << 32;             return DateTime.FromFileTimeUtc(highBits + (long)filetime.dwLowDateTime);         }     } 

interop defs are:

    [DllImport('kernel32.dll', CharSet = CharSet.Unicode, SetLastError = true)]     public static extern IntPtr FindFirstFileW(string lpFileName, out WIN32_FIND_DATAW lpFindFileData);      [DllImport('kernel32.dll', CharSet = CharSet.Unicode)]     public static extern bool FindNextFile(IntPtr hFindFile, out WIN32_FIND_DATAW lpFindFileData);      [DllImport('kernel32.dll')]     public static extern bool FindClose(IntPtr hFindFile);      [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]     public struct WIN32_FIND_DATAW {         public FileAttributes dwFileAttributes;         internal System.Runtime.InteropServices.ComTypes.FILETIME ftCreationTime;         internal System.Runtime.InteropServices.ComTypes.FILETIME ftLastAccessTime;         internal System.Runtime.InteropServices.ComTypes.FILETIME ftLastWriteTime;         public int nFileSizeHigh;         public int nFileSizeLow;         public int dwReserved0;         public int dwReserved1;         [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]         public string cFileName;         [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 14)]         public string cAlternateFileName;     }