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scm_mark_dependencies & guardians
From: |
Han-Wen |
Subject: |
scm_mark_dependencies & guardians |
Date: |
Fri, 19 Jul 2002 00:14:30 +0200 |
hi all,
Strolling through gc.c, I found a construct worthy of
Spaghetti-coding 101, namely
#define MARK scm_gc_mark
#define FNAME "scm_gc_mark"
#endif /*!MARK_DEPENDENCIES*/
/* Mark an object precisely.
*/
void
MARK (SCM p)
#define FUNC_NAME FNAME
{
:
#ifndef MARK_DEPENDENCIES
:
/* And here we define `scm_gc_mark_dependencies', by including this
* same file in itself.
*/
#define MARK scm_gc_mark_dependencies
#define FNAME "scm_gc_mark_dependencies"
#define MARK_DEPENDENCIES
#include "gc-mark.c"
#undef MARK_DEPENDENCIES
#undef MARK
#undef FNAME
The scm_gc_mark_dependencies function is used once, to detect if a
guardian object points to itself in any way. I would like to change
this code to be like
inline
scm_mark (SCM p)
{
if (marked_p(p))
return
mark_cell (p)
scm_mark_dependencies (p)
}
/* mark all objects pointed to by P */
inline scm_mark_dependencies (SCM p)
{
..
}
however, the current code is so obtuse (goto considered harmful) that
it is difficult to make out what the exact semantics of
scm_mark_dependencies () should be. For example, a self-reference to
the argument of scm_mark_dependencies() is not followed or marked, but
only in when such a mark happens in scm_mark_dependencies(), not if it
happens in subsequent recursive invocation of scm_gc_mark().
Any comments? Any objections if I change the code as I proposed? I
am a little worried that the above code may be less efficient due to
less use of goto, but that is something that can be measured.
(Some minutes later: I implemented the change, and measured a 0.4 %
speed decrease in one particular GC benchmark. I'd say that 0.4% is
not worth the spaghetti, if it were statistically significant. There
are no errors from the test suite.)
--
Han-Wen Nienhuys | address@hidden | http://www.cs.uu.nl/~hanwen
- scm_mark_dependencies & guardians,
Han-Wen <=