Tell me how to speed up the removal of empty folders / files ?

string[] dirs = Directory.EnumerateDirectories(str1, "*", SearchOption.AllDirectories).ToArray();
DirectoryInfo dirInfo = new DirectoryInfo(str1);
for (int i = dirs.Length - 1; i >= 0; i--)
   if (Directory.EnumerateFileSystemEntries(dirs[i]).Count() == 0)
       Directory.Delete(dirs[i], true);
foreach(string pathToFile in Directory.GetFiles(str1))
     if (new FileInfo(pathToFile).Length == 0)
          catch(Exception ex)
             // error

Deletes files not from all folders.


1 Answer 1

Directory.EnumerateDirectories(str1, "*", SearchOption.AllDirectories).ToArray();

Calling ToArray on this is counterproductive because this method returns directory names one by one (in a deferred fasion) as you go and request them. By using ToArray you go over directory names twice. First creating the array and then in your for loop. The EnumerateDirectories is a perfect candidate to be used with Parallel.ForEach or with AsParallel.

For example this is on my machine with 20k empty directories faster by approx 3 sec then the normal loop:

var emptyDirectories = Directory
    .EnumerateDirectories(str1, "*", SearchOption.AllDirectories)
    .Where(d => !Directory.EnumerateFileSystemEntries(d).Any())

Here you not only take the advantage of the AsParallel but also of the Any that does not have to enumerate all entries but stops as soon as at least one is found.

To delete the empty directories you can use the ForAll extension o a parallel enumeration:

var emptyDirectories =
    from d in Directory.EnumerateDirectories(str1, "*", SearchOption.AllDirectories).AsParallel()
    where !Directory.EnumerateFileSystemEntries(d).Any()
    select d;

emptyDirectories.ForAll(d => { /* delete directory */ });

The above method will of course delete only the last directory. If you want to delete directories that are empty after deleting the last empty directory you need to repeat the process:

var deleted = false;
    deleted = false;
    emptyDirectories.ForAll(d => { Directory.Delete(d); deleted = true; });

The counterpart of the EnumerateDirectories is the EnumerateFiles method that you can use same way and you can figure out this part yourself ;-)

  • 1
    \$\begingroup\$ @ArteS It depends on what you are going to do. If you want to add cancellation then you might want to use Parallel.ForEach or Task but if you are as lazy as I am, you chose the easiest solution ;-) \$\endgroup\$
    – t3chb0t
    Apr 12, 2017 at 18:07
  • \$\begingroup\$ @ArteS the same way you did it before .ForAll(d => Directory.Delete(d, true)); \$\endgroup\$
    – t3chb0t
    Apr 12, 2017 at 18:31
  • \$\begingroup\$ @ArteS this is strange because it did work for me - I tested it before posting. \$\endgroup\$
    – t3chb0t
    Apr 12, 2017 at 18:38
  • \$\begingroup\$ Updated the post \$\endgroup\$
    – GooliveR
    Apr 12, 2017 at 18:40
  • \$\begingroup\$ Sorry, earned. And how to clear empty files? \$\endgroup\$
    – GooliveR
    Apr 12, 2017 at 18:48

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