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* guardians.c (scm_guardian_zombify): Separate scanning for

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zombies from marking the pairs of the free list.
This commit is contained in:
Jim Blandy 1999-07-19 18:57:02 +00:00
parent a825bb0e2d
commit 67b2561b50
1 changed files with 11 additions and 36 deletions
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47
libguile/guardians.c
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@ -1,4 +1,4 @@
/* Copyright (C) 1998 Free Software Foundation, Inc.
/* Copyright (C) 1998, 1999 Free Software Foundation, Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@ -184,60 +184,35 @@ scm_guardian_zombify ()
of this list, so they'll be processed properly. */
for (g = first_live_guardian; g; g = g->next)
{
/* Loop through the live list and
1. move unmarked objects to the zombies tconc
2. mark the live tconc. */
/* Scan the live list for unmarked objects, and move them to the
zombies tconc. */
SCM tconc_tail = g->live.tail;
SCM prev_pair = SCM_BOOL_F;
SCM *prev_ptr = &g->live.head;
SCM pair = g->live.head;
while (pair != tconc_tail)
{
SCM next_pair = SCM_CDR (pair);
/* Since next_pair is never assigned to, and since pair is
always set to next_pair at the end of the loop, we know
that this loop always reaches every pair in the tconc
once, except the tail.
At each iteration, we either throw the pair out of the
live list, or we mark it. And when we edit a pair's CDR,
we make sure to preserve its mark bit. So when this loop
terminates, all pairs left in the live tconc (except the
tail) have been marked.
Whenever we throw out a pair, we always relink the tconc,
so the tconc list structure is valid at the end of every
iteration. */
if (SCM_NMARKEDP (SCM_CAR (pair)))
{
/* got you, zombie! */
/* out of the live list! */
if (SCM_FALSEP (prev_pair))
g->live.head = next_pair;
else
{
SCM_SETCDR (prev_pair, next_pair);
/* Don't lose the mark bit! */
SCM_SETGCMARK (prev_pair);
}
*prev_ptr = next_pair;
/* to the zombie list! */
TCONC_IN (g->zombies, SCM_CAR (pair), pair);
}
else
{
SCM_SETGCMARK (pair);
prev_pair = pair;
}
prev_ptr = SCM_CDRLOC (pair);
pair = next_pair;
}
/* Mark the tconc's tail cell. All the other pairs in the tconc
are already marked. */
SCM_SETGCMARK (tconc_tail);
/* Mark the cells of the live list. */
for (pair = g->live.head; SCM_NIMP (pair); pair = SCM_GCCDR (pair))
SCM_SETGCMARK (pair);
/* Bring the zombies back from the dead. */
scm_gc_mark (g->zombies.head);