Undo Kim's recent changes and fix the same bug differently.

(marker_blocks_pending_free): Remove.
(Fgarbage_collect): Sweep after cleaning up undo-lists.
Mark the undo lists after claning them up.
Don't free block in marker_blocks_pending_free.
(mark_buffer): Don't mark undo_list.
(gc_sweep): Sweep hash-tables and strings first.
Do free marker blocks that are empty.

1 files changed, 32 insertions, 88 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 452a1fbb2a1..0a0b25bcb7d 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -2866,10 +2866,6 @@ int marker_block_index;
 
 union Lisp_Misc *marker_free_list;
 
-/* Marker blocks which should be freed at end of GC.  */
-
-struct marker_block *marker_blocks_pending_free;
-
 /* Total number of marker blocks now in use.  */
 
 int n_marker_blocks;
@@ -2880,7 +2876,6 @@ init_marker ()
   marker_block = NULL;
   marker_block_index = MARKER_BLOCK_SIZE;
   marker_free_list = 0;
-  marker_blocks_pending_free = 0;
   n_marker_blocks = 0;
 }
 
@@ -4459,42 +4454,36 @@ returns nil, because real GC can't be done.  */)
   }
 #endif
 
-  gc_sweep ();
-
-  /* Look thru every buffer's undo list for elements that used to
-     contain update markers that were changed to Lisp_Misc_Free
-     objects and delete them.  This may leave a few cons cells
-     unchained, but we will get those on the next sweep.  */
+  /* Everything is now marked, except for the things that require special
+     finalization, i.e. the undo_list.
+     Look thru every buffer's undo list
+     for elements that update markers that were not marked,
+     and delete them.  */
   {
     register struct buffer *nextb = all_buffers;
 
     while (nextb)
       {
         /* If a buffer's undo list is Qt, that means that undo is
-           turned off in that buffer.  */
+           turned off in that buffer.  Calling truncate_undo_list on
+           Qt tends to return NULL, which effectively turns undo back on.
+           So don't call truncate_undo_list if undo_list is Qt.  */
         if (! EQ (nextb->undo_list, Qt))
           {
-            Lisp_Object tail, prev, elt, car;
+            Lisp_Object tail, prev;
             tail = nextb->undo_list;
             prev = Qnil;
             while (CONSP (tail))
               {
-                if ((elt = XCAR (tail), GC_CONSP (elt))
-                    && (car = XCAR (elt), GC_MISCP (car))
-                    && XMISCTYPE (car) == Lisp_Misc_Free)
+                if (GC_CONSP (XCAR (tail))
+                    && GC_MARKERP (XCAR (XCAR (tail)))
+                    && !XMARKER (XCAR (XCAR (tail)))->gcmarkbit)
                   {
-                    Lisp_Object cdr = XCDR (tail);
-                    /* Do not use free_cons here, as we don't know if
-                       anybody else has a pointer to these conses.  */
-                    XSETCAR (elt, Qnil);
-                    XSETCDR (elt, Qnil);
-                    XSETCAR (tail, Qnil);
-                    XSETCDR (tail, Qnil);
                     if (NILP (prev))
-                      nextb->undo_list = tail = cdr;
+                      nextb->undo_list = tail = XCDR (tail);
                     else
                       {
-                        tail = cdr;
+                        tail = XCDR (tail);
                         XSETCDR (prev, tail);
                       }
                   }
@@ -4505,22 +4494,15 @@ returns nil, because real GC can't be done.  */)
                   }
               }
           }
+        /* Now that we have stripped the elements that need not be in the
+           undo_list any more, we can finally mark the list.  */
+        mark_object (nextb->undo_list);
 
         nextb = nextb->next;
       }
   }
 
-  /* Undo lists have been cleaned up, so we can free marker blocks now.  */
-
-  {
-    struct marker_block *mblk;
-
-    while ((mblk = marker_blocks_pending_free) != 0)
-      {
-        marker_blocks_pending_free = mblk->next;
-        lisp_free (mblk);
-      }
-  }
+  gc_sweep ();
 
   /* Clear the mark bits that we set in certain root slots.  */
 
@@ -5088,41 +5070,9 @@ mark_buffer (buf)
 
   MARK_INTERVAL_TREE (BUF_INTERVALS (buffer));
 
-  if (CONSP (buffer->undo_list))
-    {
-      Lisp_Object tail;
-      tail = buffer->undo_list;
-
-      /* We mark the undo list specially because
-         its pointers to markers should be weak.  */
-
-      while (CONSP (tail))
-        {
-          register struct Lisp_Cons *ptr = XCONS (tail);
-
-          if (CONS_MARKED_P (ptr))
-            break;
-          CONS_MARK (ptr);
-          if (GC_CONSP (ptr->car)
-              && !CONS_MARKED_P (XCONS (ptr->car))
-              && GC_MARKERP (XCAR (ptr->car)))
-            {
-              CONS_MARK (XCONS (ptr->car));
-              mark_object (XCDR (ptr->car));
-            }
-          else
-            mark_object (ptr->car);
-
-          if (CONSP (ptr->cdr))
-            tail = ptr->cdr;
-          else
-            break;
-        }
-
-      mark_object (XCDR (tail));
-    }
-  else
-    mark_object (buffer->undo_list);
+  /* For now, we just don't mark the undo_list.  It's done later in
+     a special way just before the sweep phase, and after stripping
+     some of its elements that are not needed any more.  */
 
   if (buffer->overlays_before)
     {
@@ -5202,6 +5152,16 @@ survives_gc_p (obj)
 static void
 gc_sweep ()
 {
+  /* Remove or mark entries in weak hash tables.
+     This must be done before any object is unmarked.  */
+  sweep_weak_hash_tables ();
+
+  sweep_strings ();
+#ifdef GC_CHECK_STRING_BYTES
+  if (!noninteractive)
+    check_string_bytes (1);
+#endif
+
   /* Put all unmarked conses on free list */
   {
     register struct cons_block *cblk;
@@ -5252,16 +5212,6 @@ gc_sweep ()
     total_free_conses = num_free;
   }
 
-  /* Remove or mark entries in weak hash tables.
-     This must be done before any object is unmarked.  */
-  sweep_weak_hash_tables ();
-
-  sweep_strings ();
-#ifdef GC_CHECK_STRING_BYTES
-  if (!noninteractive)
-    check_string_bytes (1);
-#endif
-
   /* Put all unmarked floats on free list */
   {
     register struct float_block *fblk;
@@ -5430,7 +5380,6 @@ gc_sweep ()
     register int num_free = 0, num_used = 0;
 
     marker_free_list = 0;
-    marker_blocks_pending_free = 0;
 
     for (mblk = marker_block; mblk; mblk = *mprev)
       {
@@ -5466,13 +5415,8 @@ gc_sweep ()
             *mprev = mblk->next;
             /* Unhook from the free list.  */
             marker_free_list = mblk->markers[0].u_free.chain;
+            lisp_free (mblk);
             n_marker_blocks--;
-
-            /* It is not safe to free the marker block at this stage,
-               since there may still be pointers to these markers from
-               a buffer's undo list.  KFS 2004-05-25.  */
-            mblk->next = marker_blocks_pending_free;
-            marker_blocks_pending_free = mblk;
           }
         else
           {