Multiple uses of code-conversion-work buffer

[Stefan Monnier]

I'm seeing strange error messages (typically about incorrect search bound in
utf-8-pre-write-conversion) when working under a tty and after tracking it
down, I ended up with the following backtrace:

#1  0x080fbd94 in set_conversion_work_buffer (multibyte=1) at coding.c:6041
#2  0x080fc0d8 in run_pre_write_conversin_on_c_str (str=0x85884f4, 
    size=0x85884f8, nchars=140285938, nbytes=140285938, coding=0x85b94e0)
    at coding.c:6136
#3  0x0811424c in encode_terminal_code (src=0xb7a9fea8, src_len=46, 
    coding=0x85b94e0) at term.c:894
#4  0x081149af in write_glyphs (string=0xb7a9fc08, len=21) at term.c:970
#5  0x0805b42c in update_frame_line (f=0x85d5f58, vpos=54) at dispnew.c:5689
#6  0x0805a14d in update_frame_1 (f=0x85d5f58, force_p=1, inhibit_id_p=53)
    at dispnew.c:5187
#7  0x08057eba in update_frame (f=0x85d5f58, force_p=1, 
    inhibit_hairy_id_p=140285938) at dispnew.c:3886
#8  0x08083f6e in echo_area_display (update_frame_p=1) at xdisp.c:8192
#9  0x0807fab0 in message2_nolog (m=0x8342305 "Garbage collecting...", 
    nbytes=21, multibyte=0) at xdisp.c:6979
#10 0x0808016c in message1_nolog (m=0x8342305 "Garbage collecting...")
    at xdisp.c:7102
#11 0x081f350c in Fgarbage_collect () at alloc.c:4836
#12 0x0825de55 in Fbyte_code (bytestr=12345678, vector=138652485, 
    maxdepth=-1073749056) at bytecode.c:756
#13 0x0821aaf7 in funcall_lambda (fun=138652264, nargs=2, 
    arg_vector=0xbfffe524) at eval.c:3062
#14 0x08219f77 in Ffuncall (nargs=3, args=0xbfffe520) at eval.c:2923
#15 0x08219d30 in call2 (fn=141215530, arg1=49382712, arg2=49382876)
    at eval.c:2683
#16 0x080fbf02 in run_pre_post_conversion_on_str (str=143233993, 
    coding=0xbfffe610, encodep=1) at coding.c:6090
...

So while performing some conversion, the pre/post-conversion hook (which is
utf-8-pre-write-conversion in this case) caused a GC to happen, which in
turn caused a message to be displayed (I have garbage-collection-messages
set to t) which required conversion as well, using the same buffer that was
still being converted.

I'm not sure what's the best way to fix it.  Handa-san, any idea?
To catch this backtrace I used the patch below.


        Stefan


--- orig/src/coding.c
+++ mod/src/coding.c
@@ -6024,6 +6024,7 @@
 
 /* Name (or base name) of work buffer for code conversion.  */
 static Lisp_Object Vcode_conversion_workbuf_name;
+static Lisp_Object Vcode_conversion_workbuf_inuse;
 
 /* Set the current buffer to the working buffer prepared for
    code-conversion.  MULTIBYTE specifies the multibyteness of the
@@ -6036,6 +6037,10 @@
   Lisp_Object buffer;
   struct buffer *buf;
 
+  if (!NILP (Vcode_conversion_workbuf_inuse))
+    abort();
+    /* error ("Reusing code conversion buffer"); */
+
   buffer = Fget_buffer_create (Vcode_conversion_workbuf_name);
   buf = XBUFFER (buffer);
   delete_all_overlays (buf);
@@ -6075,6 +6080,7 @@
      unibyte<->multibyte conversion.  For that, we adjust the
      multibyteness of the working buffer to that of STR.  */
   set_conversion_work_buffer (multibyte);
+  specbind (intern ("code_conversion_workbuf_inuse"), Qt);
 
   insert_from_string (str, 0, 0,
                      SCHARS (str), SBYTES (str), 0);
@@ -6113,6 +6119,7 @@
      int *size, nchars, nbytes;
      struct coding_system *coding;
 {
+  int count = SPECPDL_INDEX ();
   struct gcpro gcpro1, gcpro2;
   struct buffer *cur = current_buffer;
   Lisp_Object old_deactivate_mark, old_last_coding_system_used;
@@ -6127,6 +6134,7 @@
      unibyte<->multibyte conversion.  For that, we adjust the
      multibyteness of the working buffer to that of STR.  */
   set_conversion_work_buffer (coding->src_multibyte);
+  specbind (intern ("code_conversion_workbuf_inuse"), Qt);
   insert_1_both (*str, nchars, nbytes, 0, 0, 0);
   UNGCPRO;
   inhibit_pre_post_conversion = 1;
@@ -6150,6 +6158,7 @@
   coding->src_multibyte
     = ! NILP (current_buffer->enable_multibyte_characters);
   set_buffer_internal (cur);
+  unbind_to (count, Qnil);
 }
 
 
@@ -7659,6 +7668,9 @@
   staticpro (&Vcode_conversion_workbuf_name);
   Vcode_conversion_workbuf_name = build_string (" *code-conversion-work*");
 
+  DEFVAR_LISP ("code_conversion_workbuf_inuse", 
&Vcode_conversion_workbuf_inuse, Doc: /*  */);
+  Vcode_conversion_workbuf_inuse = Qnil;
+
   Qtarget_idx = intern ("target-idx");
   staticpro (&Qtarget_idx);