Do not allocate huge temporary memory areas and objects while encoding

for file I/O, thus reducing an enormous memory usage for large buffers.
See http://lists.gnu.org/archive/html/emacs-devel/2013-10/msg00180.html.
* coding.h (struct coding_system): New member raw_destination.
* coding.c (setup_coding_system): Initialize it to zero.
(encode_coding_object): If raw_destination is set, do not create
dst_object.  Add comment.
* fileio.c (toplevel): New constant E_WRITE_MAX.
(e_write): Do not encode more than E_WRITE_MAX characters per one loop
iteration.  Use raw_destination if E_WRITE_MAX characters is encoded.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/coding.c b/src/coding.c
index c10fb375672..ac828a48683 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -5761,6 +5761,7 @@ setup_coding_system (Lisp_Object coding_system, struct coding_system *coding)
   coding->safe_charsets = SDATA (val);
   coding->default_char = XINT (CODING_ATTR_DEFAULT_CHAR (attrs));
   coding->carryover_bytes = 0;
+  coding->raw_destination = 0;
 
   coding_type = CODING_ATTR_TYPE (attrs);
   if (EQ (coding_type, Qundecided))
@@ -8352,6 +8353,11 @@ encode_coding_object (struct coding_system *coding,
     {
       if (BUFFERP (coding->dst_object))
         coding->dst_object = Fbuffer_string ();
+      else if (coding->raw_destination)
+        /* This is used to avoid creating huge Lisp string.
+           NOTE: caller who sets `raw_destination' is also
+           responsible for freeing `destination' buffer.  */
+        coding->dst_object = Qnil;
       else
         {
           coding->dst_object