Cache most recently spilled diversion.

* m4/output.c (tmp_file, tmp_file_owner): New variables, for
1-deep cache of spilled diversions.
(m4_tmpfile): Open in append mode, since we might revisit
diversion without closing it now.
(m4_tmpopen): Check cache first.
(m4_tmpclose): Update cache, rather than closing.  Add parameter.
(m4_tmpremove): Close cache before removing.
(m4_tmprename): Deal with open files when renaming.
(m4_output_exit): Close cache before exiting.
(make_room_for, m4_make_diversion, insert_diversion_helper):
Adjust callers.
* ltdl/m4/m4-rename.m4 (M4_RENAME): New file.
* configure.ac (M4_RENAME): Invoke it.

Signed-off-by: Eric Blake <ebb9@byu.net>

5 files changed, 119 insertions, 9 deletions

diff --git a/.gitignore b/.gitignore
index 5e8e96cc..00414942 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,7 +24,7 @@ INSTALL
 intl
 libtool
 *.log
-m4-*
+/m4-*
 Makefile
 Makefile.in
 patches
diff --git a/ChangeLog b/ChangeLog
index 5fa0473c..c7a22930 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,20 @@
 2008-12-15  Eric Blake  <ebb9@byu.net>
 
+	Cache most recently spilled diversion.
+	* m4/output.c (tmp_file, tmp_file_owner): New variables, for
+	1-deep cache of spilled diversions.
+	(m4_tmpfile): Open in append mode, since we might revisit
+	diversion without closing it now.
+	(m4_tmpopen): Check cache first.
+	(m4_tmpclose): Update cache, rather than closing.  Add parameter.
+	(m4_tmpremove): Close cache before removing.
+	(m4_tmprename): Deal with open files when renaming.
+	(m4_output_exit): Close cache before exiting.
+	(make_room_for, m4_make_diversion, insert_diversion_helper):
+	Adjust callers.
+	* ltdl/m4/m4-rename.m4 (M4_RENAME): New file.
+	* configure.ac (M4_RENAME): Invoke it.
+
 	Correctly track size of in-memory diversions.
 	* m4/output.c (insert_diversion_helper): Correctly track total
 	in-memory diversion size after undivert.
diff --git a/configure.ac b/configure.ac
index 1aa9397a..d8962cc6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -162,6 +162,7 @@ M4_ERROR
 M4_GETOPT
 M4_OBSTACK
 M4_REGEX
+M4_RENAME
 
 
 ## ------------------------ ##
diff --git a/ltdl/m4/m4-rename.m4 b/ltdl/m4/m4-rename.m4
new file mode 100644
index 00000000..892032b8
--- /dev/null
+++ b/ltdl/m4/m4-rename.m4
@@ -0,0 +1,45 @@
+#                                                            -*- Autoconf -*-
+# m4-rename.m4 -- Test the abilities of rename.
+# Written by Eric Blake <ebb9@byu.net>
+#
+# Copyright (C) 2008 Free Software Foundation, Inc
+#
+# This file is part of GNU M4.
+#
+# GNU M4 is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# GNU M4 is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# serial 1
+
+# M4_RENAME
+# ---------
+# Detect platforms like mingw where rename can't move open files.
+AC_DEFUN([M4_RENAME],
+[AC_CACHE_CHECK([whether an open file can be renamed],
+  [M4_cv_func_rename_open_file_works],
+  [AC_RUN_IFELSE([AC_LANG_PROGRAM([AC_INCLUDES_DEFAULT],
+      [FILE *f = fopen ("conftest.1", "w+");
+       int result = rename ("conftest.1", "conftest.2");
+       fclose (f); remove ("conftest.1"); remove ("conftest.2");
+       return result;])],
+    [M4_cv_func_rename_open_file_works=yes],
+    [M4_cv_func_rename_open_file_works=no],
+    [M4_cv_func_rename_open_file_works='guessing no'])])
+if test "$M4_cv_func_rename_open_file_works" = yes ; then
+  M4_rename_open_works=1
+else
+  M4_rename_open_works=0
+fi
+AC_DEFINE_UNQUOTED([RENAME_OPEN_FILE_WORKS], [$M4_rename_open_works],
+  [Define to 1 if a file can be renamed while open, or to 0 if not.])
+])
diff --git a/m4/output.c b/m4/output.c
index 1a97e3a8..2f00902c 100644
--- a/m4/output.c
+++ b/m4/output.c
@@ -112,6 +112,11 @@ static size_t output_unused;
 /* Temporary directory holding all spilled diversion files.  */
 static m4_temp_dir *output_temp_dir;
 
+/* Cache of most recently used spilled diversion file.  */
+static FILE *tmp_file;
+
+/* Diversion that owns tmp_file, or 0.  */
+static int tmp_file_owner;
 
 
 /* Internal routines.  */
@@ -214,7 +219,7 @@ m4_tmpfile (m4 *context, int divnum)
     }
   name = m4_tmpname (divnum);
   register_temp_file (output_temp_dir, name);
-  file = fopen_temp (name, O_BINARY ? "wb+" : "w+");
+  file = fopen_temp (name, O_BINARY ? "ab+" : "a+");
   if (file == NULL)
     {
       unregister_temp_file (output_temp_dir, name);
@@ -232,9 +237,17 @@ m4_tmpfile (m4 *context, int divnum)
 static FILE *
 m4_tmpopen (m4 *context, int divnum)
 {
-  const char *name = m4_tmpname (divnum);
+  const char *name;
   FILE *file;
 
+  if (tmp_file_owner == divnum)
+    {
+      if (fseeko (tmp_file, 0, SEEK_SET) != 0)
+	m4_error (context, EXIT_FAILURE, errno, NULL,
+		  _("cannot seek to beginning of diversion"));
+      return tmp_file;
+    }
+  name = m4_tmpname (divnum);
   file = fopen_temp (name, O_BINARY ? "ab+" : "a+");
   if (file == NULL)
     m4_error (context, EXIT_FAILURE, errno, NULL,
@@ -249,17 +262,36 @@ m4_tmpopen (m4 *context, int divnum)
   return file;
 }
 
-/* Close, but don't delete, a temporary FILE.  */
+/* Close, but don't delete, a temporary FILE for diversion DIVNUM.  To
+   reduce the I/O overhead of repeatedly opening and closing the same
+   file, this implementation caches the most recent spilled diversion.
+   On the other hand, keeping every spilled diversion open would run
+   into EMFILE limits.  */
 static int
-m4_tmpclose (FILE *file)
+m4_tmpclose (FILE *file, int divnum)
 {
-  return close_stream_temp (file);
+  int result = 0;
+  if (divnum != tmp_file_owner)
+    {
+      if (tmp_file_owner)
+	result = close_stream_temp (tmp_file);
+      tmp_file = file;
+      tmp_file_owner = divnum;
+    }
+  return result;
 }
 
 /* Delete a closed temporary FILE for diversion DIVNUM.  */
 static int
 m4_tmpremove (int divnum)
 {
+  if (divnum == tmp_file_owner)
+    {
+      int result = close_stream_temp (tmp_file);
+      if (result)
+	return result;
+      tmp_file_owner = 0;
+    }
   return cleanup_temp_file (output_temp_dir, m4_tmpname (divnum));
 }
 
@@ -273,6 +305,21 @@ m4_tmprename (m4 *context, int oldnum, int newnum)
   char *oldname = xstrdup (m4_tmpname (oldnum));
   const char *newname = m4_tmpname (newnum);
   register_temp_file (output_temp_dir, newname);
+  if (oldnum == tmp_file_owner)
+    {
+      /* Be careful of mingw, which can't rename an open file.  */
+      if (RENAME_OPEN_FILE_WORKS)
+	tmp_file_owner = newnum;
+      else
+	{
+	  if (close_stream_temp (tmp_file))
+	    m4_error (context, EXIT_FAILURE, errno, NULL,
+		      _("cannot close temporary file for diversion"));
+	  tmp_file_owner = 0;
+	}
+    }
+  /* Either it is safe to rename an open file, or no one should have
+     oldname open at this point.  */
   if (rename (oldname, newname))
     m4_error (context, EXIT_FAILURE, errno, NULL,
 	      _("cannot create temporary file for diversion"));
@@ -305,6 +352,8 @@ m4_output_exit (void)
      as an atexit handler, and it must not traverse stale memory.  */
   gl_oset_t table = diversion_table;
   assert (gl_oset_size (diversion_table) == 0);
+  if (tmp_file_owner)
+    m4_tmpremove (tmp_file_owner);
   diversion_table = NULL;
   gl_oset_free (table);
   obstack_free (&diversion_storage, NULL);
@@ -415,7 +464,7 @@ make_room_for (m4 *context, size_t length)
 	{
 	  FILE *file = selected_diversion->u.file;
 	  selected_diversion->u.file = NULL;
-	  if (m4_tmpclose (file) != 0)
+	  if (m4_tmpclose (file, selected_diversion->divnum) != 0)
 	    m4_error (context, 0, errno, NULL,
 		      _("cannot close temporary file for diversion"));
 	}
@@ -715,7 +764,7 @@ m4_make_diversion (m4 *context, int divnum)
 	  assert (output_diversion->divnum != 0);
 	  FILE *file = output_diversion->u.file;
 	  output_diversion->u.file = NULL;
-	  if (m4_tmpclose (file) != 0)
+	  if (m4_tmpclose (file, output_diversion->divnum) != 0)
 	    m4_error (context, 0, errno, NULL,
 		      _("cannot close temporary file for diversion"));
 	}
@@ -905,7 +954,7 @@ insert_diversion_helper (m4 *context, m4_diversion *diversion, bool escaped)
 	  FILE *file = diversion->u.file;
 	  diversion->u.file = NULL;
 	  diversion->used = 0;
-	  if (m4_tmpclose (file) != 0)
+	  if (m4_tmpclose (file, diversion->divnum) != 0)
 	    m4_error (context, 0, errno, NULL,
 		      _("cannot clean temporary file for diversion"));
 	}