Changed the internal representation of lists to (a) reduce the malloc/free

calls at list creation (from 2 to 1), (b) reduce the cost of handling empty
lists (we now never create a list internal rep for them), (c) allow
refcounting of the list internal rep. The latter permits insuring that the
pointers returned by Tcl_ListObjGetElements remain valid even if the object
shimmers away from its original list type. This is [Patch 1158008]

1 files changed, 21 insertions, 7 deletions

diff --git a/generic/tclInt.h b/generic/tclInt.h
index 4521ff4..cb72307 100644
--- a/generic/tclInt.h
+++ b/generic/tclInt.h
@@ -12,7 +12,7 @@
  * See the file "license.terms" for information on usage and redistribution
  * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclInt.h,v 1.218 2005/04/01 16:18:59 msofer Exp $
+ * RCS: @(#) $Id: tclInt.h,v 1.219 2005/04/02 02:08:37 msofer Exp $
  */
 
 #ifndef _TCLINT
@@ -1618,20 +1618,34 @@ typedef enum TclEolTranslation {
 
 /*
  * The structure used as the internal representation of Tcl list
- * objects. This is an array of pointers to the element objects. This array
- * is grown (reallocated and copied) as necessary to hold all the list's
- * element pointers. The array might contain more slots than currently used
- * to hold all element pointers. This is done to make append operations
- * faster.
+ * objects. This struct is grown (reallocated and copied) as necessary to hold
+ * all the list's element pointers. The struct might contain more slots than
+ * currently used to hold all element pointers. This is done to make append
+ * operations faster.
  */
 
 typedef struct List {
+    int refCount;
     int maxElemCount;		/* Total number of element array slots. */
     int elemCount;		/* Current number of list elements. */
-    Tcl_Obj **elements;		/* Array of pointers to element objects. */
+    Tcl_Obj *elements;		/* First list element; the struct is grown to
+				 * accomodate all elements. */
 } List;
 
 /*
+ * Macro used to get the elements of a list object - do NOT forget to verify
+ * that it is of list type before using!
+ */
+
+#define TclListObjGetElements(listPtr, objc, objv) \
+    { \
+	List *listRepPtr = \
+	    (List *) (listPtr)->internalRep.twoPtrValue.ptr1;\
+	(objc) = listRepPtr->elemCount;\
+	(objv) = &listRepPtr->elements;\
+    }
+
+/*
  *----------------------------------------------------------------
  * Data structures related to the filesystem internals
  *----------------------------------------------------------------