Fix bug #12587 with slow startup on MS-Windows with Netlogon service.

src/fileio.c (check_existing): New function.
 (make_temp_name, Ffile_exists_p, Ffile_writable_p): Call it
 instead of calling 'stat', when what's needed is to check whether
 a file exists.  This avoids expensive system calls on MS-Windows.
 src/w32.c (init_environment): Call 'check_existing' instead of 'stat'.
 src/lread.c (openp) [WINDOWSNT]: Call 'access' instead of 'stat' to
 determine whether a file exists and is not a directory.
 src/lisp.h (check_existing): Add prototype.

src/ChangeLog

@@ -1,3 +1,19 @@
+2012-10-12  Eli Zaretskii  <eliz@gnu.org>
+
+	* fileio.c (check_existing): New function.
+	(make_temp_name, Ffile_exists_p, Ffile_writable_p): Call it
+	instead of calling 'stat', when what's needed is to check whether
+	a file exists.  This avoids expensive system calls on MS-Windows.
+	(Bug#12587)
+
+	* w32.c (init_environment): Call 'check_existing' instead of
+	'stat'.
+
+	* lread.c (openp) [WINDOWSNT]: Call 'access' instead of 'stat' to
+	determine whether a file exists and is not a directory.
+
+	* lisp.h (check_existing): Add prototype.
+
 2012-10-12  Jan Djärv  <jan.h.d@swipnet.se>
 
 	* nsfont.m (nsfont_open): Remove font cache, it is not GC correct.

src/fileio.c

@@ -52,6 +52,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #define NOMINMAX 1
 #include <windows.h>
 #include <fcntl.h>
+#include <sys/file.h>
 #endif /* not WINDOWSNT */
 
 #ifdef MSDOS
@@ -668,7 +669,6 @@ make_temp_name (Lisp_Object prefix, bool base64_p)
 
   while (1)
     {
-      struct stat ignored;
       unsigned num = make_temp_name_count;
 
       p[0] = make_temp_name_tbl[num & 63], num >>= 6;
@@ -680,7 +680,7 @@ make_temp_name (Lisp_Object prefix, bool base64_p)
       make_temp_name_count += 25229;
       make_temp_name_count %= 225307;
 
-      if (stat (data, &ignored) < 0)
+      if (!check_existing (data))
 	{
 	  /* We want to return only if errno is ENOENT.  */
 	  if (errno == ENOENT)
@@ -2423,6 +2423,21 @@ On Unix, this is a name starting with a `/' or a `~'.  */)
   return file_name_absolute_p (SSDATA (filename)) ? Qt : Qnil;
 }
 
+/* Return true if FILENAME exists.  */
+bool
+check_existing (const char *filename)
+{
+#ifdef DOS_NT
+  /* The full emulation of Posix 'stat' is too expensive on
+     DOS/Windows, when all we want to know is whether the file exists.
+     So we use 'access' instead, which is much more lightweight.  */
+  return (access (filename, F_OK) >= 0);
+#else
+  struct stat st;
+  return (stat (filename, &st) >= 0);
+#endif
+}
+
 /* Return true if file FILENAME exists and can be executed.  */
 
 static bool
@@ -2490,7 +2505,6 @@ Use `file-symlink-p' to test for such links.  */)
 {
   Lisp_Object absname;
   Lisp_Object handler;
-  struct stat statbuf;
 
   CHECK_STRING (filename);
   absname = Fexpand_file_name (filename, Qnil);
@@ -2503,7 +2517,7 @@ Use `file-symlink-p' to test for such links.  */)
 
   absname = ENCODE_FILE (absname);
 
-  return (stat (SSDATA (absname), &statbuf) >= 0) ? Qt : Qnil;
+  return (check_existing (SSDATA (absname))) ? Qt : Qnil;
 }
 
 DEFUN ("file-executable-p", Ffile_executable_p, Sfile_executable_p, 1, 1, 0,
@@ -2584,7 +2598,6 @@ DEFUN ("file-writable-p", Ffile_writable_p, Sfile_writable_p, 1, 1, 0,
 {
   Lisp_Object absname, dir, encoded;
   Lisp_Object handler;
-  struct stat statbuf;
 
   CHECK_STRING (filename);
   absname = Fexpand_file_name (filename, Qnil);
@@ -2596,7 +2609,7 @@ DEFUN ("file-writable-p", Ffile_writable_p, Sfile_writable_p, 1, 1, 0,
     return call2 (handler, Qfile_writable_p, absname);
 
   encoded = ENCODE_FILE (absname);
-  if (stat (SSDATA (encoded), &statbuf) >= 0)
+  if (check_existing (SSDATA (encoded)))
     return (check_writable (SSDATA (encoded))
 	    ? Qt : Qnil);
 
@@ -2611,9 +2624,7 @@ DEFUN ("file-writable-p", Ffile_writable_p, Sfile_writable_p, 1, 1, 0,
   /* The read-only attribute of the parent directory doesn't affect
      whether a file or directory can be created within it.  Some day we
      should check ACLs though, which do affect this.  */
-  if (stat (SDATA (dir), &statbuf) < 0)
-    return Qnil;
-  return S_ISDIR (statbuf.st_mode) ? Qt : Qnil;
+  return (access (SDATA (dir), D_OK) < 0) ? Qnil : Qt;
 #else
   return (check_writable (!NILP (dir) ? SSDATA (dir) : "")
 	  ? Qt : Qnil);

src/lisp.h

@@ -3182,6 +3182,7 @@ extern void internal_delete_file (Lisp_Object);
 extern void syms_of_fileio (void);
 extern Lisp_Object make_temp_name (Lisp_Object, bool);
 extern Lisp_Object Qdelete_file;
+extern bool check_existing (const char *);
 
 /* Defined in search.c.  */
 extern void shrink_regexp_cache (void);

src/lread.c

@@ -1449,7 +1449,6 @@ openp (Lisp_Object path, Lisp_Object str, Lisp_Object suffixes, Lisp_Object *sto
   bool absolute = 0;
   ptrdiff_t want_length;
   Lisp_Object filename;
-  struct stat st;
   struct gcpro gcpro1, gcpro2, gcpro3, gcpro4, gcpro5, gcpro6;
   Lisp_Object string, tail, encoded_fn;
   ptrdiff_t max_suffix_len = 0;
@@ -1543,11 +1542,18 @@ openp (Lisp_Object path, Lisp_Object str, Lisp_Object suffixes, Lisp_Object *sto
 	    }
 	  else
 	    {
+#ifndef WINDOWSNT
+	      struct stat st;
+#endif
 	      const char *pfn;
 
 	      encoded_fn = ENCODE_FILE (string);
 	      pfn = SSDATA (encoded_fn);
+#ifdef WINDOWSNT
+	      exists = access (pfn, F_OK) == 0 && access (pfn, D_OK) < 0;
+#else
 	      exists = (stat (pfn, &st) == 0 && ! S_ISDIR (st.st_mode));
+#endif
 	      if (exists)
 		{
 		  /* Check that we can access or open it.  */

src/w32.c

@@ -1612,7 +1612,6 @@ init_environment (char ** argv)
     LPBYTE lpval;
     DWORD dwType;
     char locale_name[32];
-    struct stat ignored;
     char default_home[MAX_PATH];
     int appdata = 0;
 
@@ -1653,7 +1652,7 @@ init_environment (char ** argv)
     /* For backwards compatibility, check if a .emacs file exists in C:/
        If not, then we can try to default to the appdata directory under the
        user's profile, which is more likely to be writable.   */
-    if (stat ("C:/.emacs", &ignored) < 0)
+    if (check_existing ("C:/.emacs"))
       {
 	HRESULT profile_result;
 	/* Dynamically load ShGetFolderPath, as it won't exist on versions