Re: empty-directory predicate, native implementation

[Arthur Miller <arthur.miller@live.com>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Michael Albinus <michael.albinus@gmx.de>
>> Cc: Arthur Miller <arthur.miller@live.com>,  emacs-devel@gnu.org
>> Date: Tue, 13 Oct 2020 20:44:18 +0200
>> 
>> > As a bonus, we will be able to return the file names we read, not just
>> > ignore them.
>> 
>> I agree with your proposal. However, I don't see why it is a bonus to
>> know which file names have read already, because they are taken in
>> random order.
>
> The order depends on the filesystem.  For example, MS-Windows
> filesystems always report in alphabetic order.
>
>> I fail to see how does it help, whether a file name is returned
>> under the first N matches, or not.
>
> Well, it is easy to disregard the names if they aren't needed.

Your idea was definitely much simpler to implement, rather trivial :-).
I just tested for myself, and it seems to work well.

The only thing I am not sure about is how to deal with 0 count; I
mean if user explicitly ask for 0 count; the case when count is not
NILP. I have chosen not to deal with it all, I check for zer set
explicit limit for count to be [1,COUNT]. I am not sure if that is best
thing to do; maybe just to return Qnil? I am probably doing something
else wrong, advice apprecaiated. 

I had some problems until I realized i used wrong number converter; I
used fixnum, seems like I need fixnat. I am still not sure if I am
correct but it seems to work now. 

I tested this compared to my old "native" predicate, on GNU/Linux only
and just to run naked predicate on a big number of dirs, and it seems to
be just very slight difference; ~0.002 vs ~0.004 definitely not dramatic
as entire decimal place.

I needed to "touch" 2 other files due to chagned signature of
directory_files: lisp.h and sysdep.c.

In attached .el file are two small tests (I run them with M-:).


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--- src/dired.c	2020-10-14 03:35:16.781786426 +0200
+++ ../dired2.c	2020-10-14 03:35:05.271568190 +0200
@@ -20,6 +20,7 @@
 
 #include <config.h>
 
+#include <stddef.h>
 #include <sys/stat.h>
 
 #ifdef HAVE_PWD_H
@@ -165,7 +166,7 @@
 Lisp_Object
 directory_files_internal (Lisp_Object directory, Lisp_Object full,
 			  Lisp_Object match, Lisp_Object nosort, bool attrs,
-			  Lisp_Object id_format)
+			  Lisp_Object id_format, Lisp_Object count_to_return)
 {
   if (!NILP (match))
     CHECK_STRING (match);
@@ -223,7 +224,14 @@
 #ifdef WINDOWSNT
   case_table = BVAR (&buffer_defaults, case_canon_table);
 #endif
-
+  
+  ptrdiff_t ind = 0, last = 0;
+  if(!NILP(count_to_return) && FIXNATP(count_to_return))
+      last = XFIXNAT(count_to_return);
+  
+  if(!last)
+    last = 1;
+  
   /* Read directory entries and accumulate them into LIST.  */
   Lisp_Object list = Qnil;
   for (struct dirent *dp; (dp = read_dirent (d, directory)); )
@@ -267,6 +275,13 @@
       else
 	finalname = name;
 
+      if(!NILP(count_to_return) && FIXNATP(count_to_return))
+        {
+          if(ind == last)
+            break;
+          ind ++;
+        }
+      
       list = Fcons (attrs ? Fcons (finalname, fileattrs) : finalname, list);
     }
 
@@ -282,13 +297,13 @@
   if (NILP (nosort))
     list = Fsort (Fnreverse (list),
 		  attrs ? Qfile_attributes_lessp : Qstring_lessp);
-
+  
   (void) directory_volatile;
   return list;
 }
 
 
-DEFUN ("directory-files", Fdirectory_files, Sdirectory_files, 1, 4, 0,
+DEFUN ("directory-files", Fdirectory_files, Sdirectory_files, 1, 5, 0,
        doc: /* Return a list of names of files in DIRECTORY.
 There are three optional arguments:
 If FULL is non-nil, return absolute file names.  Otherwise return names
@@ -296,9 +311,14 @@
 If MATCH is non-nil, mention only file names that match the regexp MATCH.
 If NOSORT is non-nil, the list is not sorted--its order is unpredictable.
  Otherwise, the list returned is sorted with `string-lessp'.
- NOSORT is useful if you plan to sort the result yourself.  */)
+ NOSORT is useful if you plan to sort the result yourself. 
+If COUNT is  non-nil, the function will return max (COUNT,length)
+ files, where length means number of files in directory. Order
+ in which files are returned is not guaranteed and is file system and
+ OS dependent. COUNT has to be an integral number in interval
+ [1,COUNT]. */) 
   (Lisp_Object directory, Lisp_Object full, Lisp_Object match,
-   Lisp_Object nosort)
+   Lisp_Object nosort, Lisp_Object count)
 {
   directory = Fexpand_file_name (directory, Qnil);
 
@@ -306,14 +326,15 @@
      call the corresponding file name handler.  */
   Lisp_Object handler = Ffind_file_name_handler (directory, Qdirectory_files);
   if (!NILP (handler))
-    return call5 (handler, Qdirectory_files, directory,
-                  full, match, nosort);
+    return call6 (handler, Qdirectory_files, directory,
+                  full, match, nosort, count);
 
-  return directory_files_internal (directory, full, match, nosort, false, Qnil);
+  return directory_files_internal (directory, full, match, nosort,
+                                   false, Qnil, count);
 }
 
 DEFUN ("directory-files-and-attributes", Fdirectory_files_and_attributes,
-       Sdirectory_files_and_attributes, 1, 5, 0,
+       Sdirectory_files_and_attributes, 1, 6, 0,
        doc: /* Return a list of names of files and their attributes in DIRECTORY.
 Value is a list of the form:
 
@@ -331,9 +352,14 @@
 ID-FORMAT specifies the preferred format of attributes uid and gid, see
 `file-attributes' for further documentation.
 On MS-Windows, performance depends on `w32-get-true-file-attributes',
-which see.  */)
-  (Lisp_Object directory, Lisp_Object full, Lisp_Object match,
-   Lisp_Object nosort, Lisp_Object id_format)
+which see. 
+If COUNT is  non-nil, the function will return max (COUNT,length)
+ files, where length means number of files in directory. Order
+ in which files are returned is not guaranteed and is file system and
+ OS dependent. COUNT has to be an integral number in interval
+ [1,COUNT]. */)
+(Lisp_Object directory, Lisp_Object full, Lisp_Object match,
+   Lisp_Object nosort, Lisp_Object id_format, Lisp_Object count)
 {
   directory = Fexpand_file_name (directory, Qnil);
 
@@ -342,11 +368,11 @@
   Lisp_Object handler
     = Ffind_file_name_handler (directory, Qdirectory_files_and_attributes);
   if (!NILP (handler))
-    return call6 (handler, Qdirectory_files_and_attributes,
-                  directory, full, match, nosort, id_format);
+    return call7 (handler, Qdirectory_files_and_attributes,
+                  directory, full, match, nosort, id_format, count);
 
   return directory_files_internal (directory, full, match, nosort,
-				   true, id_format);
+				   true, id_format, count);
 }
 
 \f
@@ -929,7 +955,7 @@
   struct stat s;
 
   /* An array to hold the mode string generated by filemodestring,
-     including its terminating space and null byte.  */
+     including its terminating space and NUL byte.  */
   char modes[sizeof "-rwxr-xr-x "];
 
   char *uname = NULL, *gname = NULL;

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--- src/sysdep.c	2020-10-13 23:22:37.521367461 +0200
+++ ../sysdep.c	2020-10-13 22:53:04.272682143 +0200
@@ -2892,7 +2892,8 @@
      process.  */
   procdir = build_string ("/proc");
   match = build_string ("[0-9]+");
-  proclist = directory_files_internal (procdir, Qnil, match, Qt, false, Qnil);
+  proclist = directory_files_internal (procdir, Qnil, match, Qt,
+                                       false, Qnil, Qnil);
 
   /* `proclist' gives process IDs as strings.  Destructively convert
      each string into a number.  */

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--- src/lisp.h	2020-10-13 23:20:23.555386699 +0200
+++ ../lisp.h	2020-10-13 22:47:04.192203245 +0200
@@ -4633,7 +4633,7 @@
 extern void syms_of_dired (void);
 extern Lisp_Object directory_files_internal (Lisp_Object, Lisp_Object,
                                              Lisp_Object, Lisp_Object,
-                                             bool, Lisp_Object);
+                                             bool, Lisp_Object, Lisp_Object);
 
 /* Defined in term.c.  */
 extern int *char_ins_del_vector;

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(require 'dired)

(defvar nodots "^\\([^.]\\|\\.\\([^.]\\|\\..\\)\\).*")

(defun dired-go-to-first ()
    (interactive)
    (goto-char (point-min))
    (dired-next-line 1)
    (skip-chars-forward " \n\t"))

(defun dired-is-empty-p (directory-name)
  (null (directory-files directory-name nil nodots t 1)))

(defun directory-number-files (directory-name &optional omit-filter)
  (length (directory-files directory-name nil omit-filter t)))

(defun dired-mark-empty-dirs ()
  (interactive)
  (when (equal major-mode 'dired-mode)
    (let ((curr-dir))
      (save-excursion
        (dired-go-to-first)
        
        (while (not (eobp))
          (setq curr-dir (dired-file-name-at-point))
          (cond ((or (null curr-dir)
                     (string= curr-dir ".")
                     (string= curr-dir ".."))
                     ;; do nothing here
                 )
                ((file-directory-p curr-dir)
                 (when (dired-is-empty-p curr-dir)
                   (dired-mark 1)
                   (dired-previous-line 1))))
          (dired-next-line 1))))))

(defun test-1 (dir-name count)
  "Ask for COUNT number of files from directory DIR-NAME."
  (let ((max (length (directory-files dir-name nil nil t)))
        (res (length (directory-files dir-name nil nil t count))))
    (cond ((>= max count)
           (if (= res count)
               (message "passed: asked: %d get: %d number files in dir: %d" count
                        res max)
             (message "not-passed: asked: %s get: %s number files in dir: %s" count
                      res max)))
          ((< max count)
           (if (< res count)
              (message "passed: asked: %d get: %d number files in dir: %d" count
                       res max)
            (message "not-passed: asked: %s get: %s number files in dir: %s" count
                     res max)))
          (t
           (message "Invalid case!")))))

(defun test-2 (dir-name count)
  "Ask for random number of files in interval [1,COUNT] files from every subdir
of directory DIR-NAME."
  (let ((dirs (directory-files dir-name t nodots t)))
    (dolist (curr-dir dirs)
      (when (file-directory-p curr-dir)
        (test-1 curr-dir (+ 1 (random count)))))))

;;(benchmark-run-compiled 10 (dired-is-empty-p "/some/path"))

;; must be in some dired buffer for this
;;(benchmark-run-compiled 10 (dired-mark-empty-dirs))