Is there a faster way to scan through a directory recursively in .NET?

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

I recently (2020) discovered this post because of a need to count files and directories across slow connections, and this was the fastest implementation I could come up with. The .NET enumeration methods (GetFiles(), GetDirectories()) perform a lot of under-the-hood work that slows them down tremendously by comparison.

This solution utilizes the Win32 API and .NET's Parallel.ForEach() to leverage the threadpool to maximize performance.

P/Invoke:

/// <summary>
/// https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-findfirstfilew
/// </summary>
[DllImport("kernel32.dll", SetLastError = true)]
public static extern IntPtr FindFirstFile(
    string lpFileName,
    ref WIN32_FIND_DATA lpFindFileData
    );

/// <summary>
/// https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-findnextfilew
/// </summary>
[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool FindNextFile(
    IntPtr hFindFile,
    ref WIN32_FIND_DATA lpFindFileData
    );

/// <summary>
/// https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-findclose
/// </summary>
[DllImport("kernel32.dll", SetLastError = true)]
public static extern bool FindClose(
    IntPtr hFindFile
    );

Method:

public static Tuple<long, long> CountFilesDirectories(
    string path,
    CancellationToken token
    )
{
    if (String.IsNullOrWhiteSpace(path))
        throw new ArgumentNullException("path", "The provided path is NULL or empty.");

    // If the provided path doesn't end in a backslash, append one.
    if (path.Last() != '\\')
        path += '\\';

    IntPtr hFile = IntPtr.Zero;
    Win32.Kernel32.WIN32_FIND_DATA fd = new Win32.Kernel32.WIN32_FIND_DATA();

    long files = 0;
    long dirs = 0;

    try
    {
        hFile = Win32.Kernel32.FindFirstFile(
            path + "*", // Discover all files/folders by ending a directory with "*", e.g. "X:\*".
            ref fd
            );

        // If we encounter an error, or there are no files/directories, we return no entries.
        if (hFile.ToInt64() == -1)
            return Tuple.Create<long, long>(0, 0);

        //
        // Find (and count) each file/directory, then iterate through each directory in parallel to maximize performance.
        //

        List<string> directories = new List<string>();

        do
        {
            // If a directory (and not a Reparse Point), and the name is not "." or ".." which exist as concepts in the file system,
            // count the directory and add it to a list so we can iterate over it in parallel later on to maximize performance.
            if ((fd.dwFileAttributes & FileAttributes.Directory) != 0 &&
                (fd.dwFileAttributes & FileAttributes.ReparsePoint) == 0 &&
                fd.cFileName != "." && fd.cFileName != "..")
            {
                directories.Add(System.IO.Path.Combine(path, fd.cFileName));
                dirs++;
            }
            // Otherwise, if this is a file ("archive"), increment the file count.
            else if ((fd.dwFileAttributes & FileAttributes.Archive) != 0)
            {
                files++;
            }
        }
        while (Win32.Kernel32.FindNextFile(hFile, ref fd));

        // Iterate over each discovered directory in parallel to maximize file/directory counting performance,
        // calling itself recursively to traverse each directory completely.
        Parallel.ForEach(
            directories,
            new ParallelOptions()
            {
                CancellationToken = token
            },
            directory =>
            {
                var count = CountFilesDirectories(
                    directory,
                    token
                    );

                lock (directories)
                {
                    files += count.Item1;
                    dirs += count.Item2;
                }
            });
    }
    catch (Exception)
    {
        // Handle as desired.
    }
    finally
    {
        if (hFile.ToInt64() != 0)
            Win32.Kernel32.FindClose(hFile);
    }

    return Tuple.Create<long, long>(files, dirs);
}

On my local system, the performance of GetFiles()/GetDirectories() can be close to this, but across slower connections (VPNs, etc.) I found that this is tremendously faster—45 minutes vs. 90 seconds to access a remote directory of ~40k files, ~40 GB in size.

This can also fairly easily be modified to include other data, like the total file size of all files counted, or rapidly recursing through and deleting empty directories, starting at the furthest branch.

Answer 2

Recently I have the same question, I think it is also good to output all folders and files into a text file, and then use streamreader to read the text file, do what you want to process with multi-thread.

cmd.exe /u /c dir "M:\" /s /b >"c:\flist1.txt"

[update] Hi Moby, you are correct. My approach is slower due to overhead of reading back the output text file. Actually I took some time to test the top answer and cmd.exe with 2 million files.

The top answer: 2010100 files, time: 53023
cmd.exe method: 2010100 files, cmd time: 64907, scan output file time: 19832.

The top answer method(53023) is faster than cmd.exe(64907), not to mention how to improve reading output text file. Although my original point is to provide a not-too-bad answer, still feel sorry, ha.

Answer 3

There is a long history of the .NET file enumeration methods being slow. The issue is there is not an instantaneous way of enumerating large directory structures. Even the accepted answer here has it's issues with GC allocations.

The best I've been able do is wrapped up in my library and exposed as the FileFile (source) class in the CSharpTest.Net.IO namespace. This class can enumerate files and folders without unneeded GC allocations and string marshaling.

The usage is simple enough, and the RaiseOnAccessDenied property will skip the directories and files the user does not have access to:

    private static long SizeOf(string directory)
    {
        var fcounter = new CSharpTest.Net.IO.FindFile(directory, "*", true, true, true);
        fcounter.RaiseOnAccessDenied = false;

        long size = 0, total = 0;
        fcounter.FileFound +=
            (o, e) =>
            {
                if (!e.IsDirectory)
                {
                    Interlocked.Increment(ref total);
                    size += e.Length;
                }
            };

        Stopwatch sw = Stopwatch.StartNew();
        fcounter.Find();
        Console.WriteLine("Enumerated {0:n0} files totaling {1:n0} bytes in {2:n3} seconds.",
                          total, size, sw.Elapsed.TotalSeconds);
        return size;
    }

For my local C:\ drive this outputs the following:

Enumerated 810,046 files totaling 307,707,792,662 bytes in 232.876 seconds.

Your mileage may vary by drive speed, but this is the fastest method I've found of enumerating files in managed code. The event parameter is a mutating class of type FindFile.FileFoundEventArgs so be sure you do not keep a reference to it as it's values will change for each event raised.

You might also note that the DateTime's exposed are only in UTC. The reason is that the conversion to local time is semi-expensive. You might consider using UTC times to improve performance rather than converting these to local time.

Answer 4

I just ran across this. Nice implementation of the native version.

This version, while still slower than the version that uses FindFirst and FindNext, is quite a bit faster than the your original .NET version.

    static List<Info> RecursiveMovieFolderScan(string path)
    {
        var info = new List<Info>();
        var dirInfo = new DirectoryInfo(path);
        foreach (var entry in dirInfo.GetFileSystemInfos())
        {
            bool isDir = (entry.Attributes & FileAttributes.Directory) != 0;
            if (isDir)
            {
                info.AddRange(RecursiveMovieFolderScan(entry.FullName));
            }
            info.Add(new Info()
            {
                IsDirectory = isDir,
                CreatedDate = entry.CreationTimeUtc,
                ModifiedDate = entry.LastWriteTimeUtc,
                Path = entry.FullName
            });
        }
        return info;
    }

It should produce the same output as your native version. My testing shows that this version takes about 1.7 times as long as the version that uses FindFirst and FindNext. Timings obtained in release mode running without the debugger attached.

Curiously, changing the GetFileSystemInfos to EnumerateFileSystemInfos adds about 5% to the running time in my tests. I rather expected it to run at the same speed or possibly faster because it didn't have to create the array of FileSystemInfo objects.

The following code is shorter still, because it lets the Framework take care of recursion. But it's a good 15% to 20% slower than the version above.

    static List<Info> RecursiveScan3(string path)
    {
        var info = new List<Info>();

        var dirInfo = new DirectoryInfo(path);
        foreach (var entry in dirInfo.EnumerateFileSystemInfos("*", SearchOption.AllDirectories))
        {
            info.Add(new Info()
            {
                IsDirectory = (entry.Attributes & FileAttributes.Directory) != 0,
                CreatedDate = entry.CreationTimeUtc,
                ModifiedDate = entry.LastWriteTimeUtc,
                Path = entry.FullName
            });
        }
        return info;
    }

Again, if you change that to GetFileSystemInfos, it will be slightly (but only slightly) faster.

For my purposes, the first solution above is quite fast enough. The native version runs in about 1.6 seconds. The version that uses DirectoryInfo runs in about 2.9 seconds. I suppose if I were running these scans very frequently, I'd change my mind.

Answer 5

Its pretty shallow, 371 dirs with average of 10 files in each directory. some dirs contain other sub dirs

This is just a comment, but your numbers do appear to be quite high. I ran the below using essentially the same recursive method you are using and my times are far lower despite creating string output.

    public void RecurseTest(DirectoryInfo dirInfo, 
                            StringBuilder sb, 
                            int depth)
    {
        _dirCounter++;
        if (depth > _maxDepth)
            _maxDepth = depth;

        var array = dirInfo.GetFileSystemInfos();
        foreach (var item in array)
        {
            sb.Append(item.FullName);
            if (item is DirectoryInfo)
            {
                sb.Append(" (D)");
                sb.AppendLine();

                RecurseTest(item as DirectoryInfo, sb, depth+1);
            }
            else
            { _fileCounter++; }

            sb.AppendLine();
        }
    }

I ran the above code on a number of different directories. On my machine the 2nd call to scan a directory tree was usually faster due to caching either by the runtime or the file system. Note that this system isn't anything too special, just a 1yr old development workstation.

// cached call
Dirs = 150, files = 420, max depth = 5
Time taken = 53 milliseconds

// cached call
Dirs = 1117, files = 9076, max depth = 11
Time taken = 433 milliseconds

// first call
Dirs = 1052, files = 5903, max depth = 12
Time taken = 11921 milliseconds

// first call
Dirs = 793, files = 10748, max depth = 10
Time taken = 5433 milliseconds (2nd run 363 milliseconds)

Concerned that I wasn't getting the create and modified date, the code was modified to output this as well with the following times.

// now grabbing last update and creation time.
Dirs = 150, files = 420, max depth = 5
Time taken = 103 milliseconds (2nd run 93 milliseconds)

Dirs = 1117, files = 9076, max depth = 11
Time taken = 992 milliseconds (2nd run 984 milliseconds)

Dirs = 793, files = 10748, max depth = 10
Time taken = 1382 milliseconds (2nd run 735 milliseconds)

Dirs = 1052, files = 5903, max depth = 12
Time taken = 936 milliseconds (2nd run 595 milliseconds)

Note: System.Diagnostics.StopWatch class used for timing.

Answer 6

I'd use or base myself on this multi-threaded library: http://www.codeproject.com/KB/files/FileFind.aspx

Answer 7

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;
    }

Answer 8

Depending on how much time you're trying to shave off the function, it may be worth your while to call the Win32 API functions directly, since the existing API does a lot of extra processing to check things that you may not be interested in.

If you haven't done so already, and assuming you don't intend to contribute to the Mono project, I would strongly recommend downloading Reflector and having a look at how Microsoft implemented the API calls you're currently using. This will give you an idea of what you need to call and what you can leave out.

You might, for example, opt to create an iterator that yields directory names instead of a function that returns a list, that way you don't end up iterating over the same list of names two or three times through all the various levels of code.

Answer 9

try this (i.e. do the initialization first, and then reuse your list and your directoryInfo objects):

  static List<Info> RecursiveMovieFolderScan1() {
      var info = new List<Info>();
      var dirInfo = new DirectoryInfo(path);
      RecursiveMovieFolderScan(dirInfo, info);
      return info;
  } 

  static List<Info> RecursiveMovieFolderScan(DirectoryInfo dirInfo, List<Info> info){

    foreach (var dir in dirInfo.GetDirectories()) {

        info.Add(new Info() {
            IsDirectory = true,
            CreatedDate = dir.CreationTimeUtc,
            ModifiedDate = dir.LastWriteTimeUtc,
            Path = dir.FullName
        });

        RecursiveMovieFolderScan(dir, info);
    }

    foreach (var file in dirInfo.GetFiles()) {
        info.Add(new Info()
        {
            IsDirectory = false,
            CreatedDate = file.CreationTimeUtc,
            ModifiedDate = file.LastWriteTimeUtc,
            Path = file.FullName
        });
    }

    return info; 
}