Description:
------------
hi

user 1: opendir("mydir");

at the same time:
user 2: rmdir("mydir");

the dir is removed, but user1 tries to read it:
user 1: readdir(); // no error here

or you can just simply test this:

$handle = opendir('mydir');
rmdir("mydir");
// no error here
// the dir is empty so "echo $file" is not executed, but the dir does not exists, not empty
while (false !== ($file = readdir($handle))) echo $file;