Question

Is it safe to read directory entries via readdir() or scandir() while files are being created or deleted in this directory? Should I prefer one over the other?

EDIT: When I say “safe” I mean entries returned by these functions are valid and can be operated without crashing the program.

Thanks.

Answer 1

It depends by what you mean as “safe”. They are safe in the sense that they should not crash your program. However, if you are creating/deleting files as you are reading/scanning that directory, the set of files you get back might not be up-to-date.

When reading/scanning a directory for directory entries, the file pointer (a directory is just a special type of file), moves forward. However, depending upon the file system, there may be nothing to prevent new files from being created in an empty directory entry slot behind your file pointer. Consequently, newly added directory entries may not be immediately detected by readdir()/scandir(). Similar reasoning applies for file deletion / directory entry removal.

Hope this helps.