wingo pushed a commit to branch wip-whippet
in repository guile.
commit cc2a90b4949fa91e7fca814882a83e46a69260f8
Author: Andy Wingo <wi...@igalia.com>
AuthorDate: Mon May 12 13:37:18 2025 +0200
bdw: Fix detection of objects on free-lists
I am not sure about ephemerons and finalizers, though.
---
src/bdw.c | 25 ++++++++++++-------------
1 file changed, 12 insertions(+), 13 deletions(-)
diff --git a/src/bdw.c b/src/bdw.c
index a50994d7c..e6b3f4ef5 100644
--- a/src/bdw.c
+++ b/src/bdw.c
@@ -52,7 +52,6 @@
#define GC_INLINE_FREELIST_COUNT (256U / GC_INLINE_GRANULE_BYTES)
struct gc_heap {
- struct gc_heap *freelist; // see mark_heap
struct gc_heap_roots *roots;
struct gc_mutator *mutators;
struct gc_event_listener event_listener;
@@ -315,7 +314,7 @@ mark_ephemeron(GC_word *addr, struct GC_ms_entry
*mark_stack_ptr,
struct gc_ephemeron *ephemeron = (struct gc_ephemeron*) addr;
- // If this ephemeron is on a freelist, its first word will be a
+ // If this ephemeron is on a freelist, its first word will be a possibly-null
// freelist link and everything else will be NULL.
if (!gc_ref_value(gc_edge_ref(gc_ephemeron_value_edge(ephemeron)))) {
bdw_mark_edge(gc_edge(addr), NULL, &state);
@@ -344,7 +343,7 @@ mark_finalizer(GC_word *addr, struct GC_ms_entry
*mark_stack_ptr,
struct gc_finalizer *finalizer = (struct gc_finalizer*) addr;
- // If this ephemeron is on a freelist, its first word will be a
+ // If this ephemeron is on a freelist, its first word will be a possibly-null
// freelist link and everything else will be NULL.
if (!gc_ref_value(gc_finalizer_object(finalizer))) {
bdw_mark_edge(gc_edge(addr), NULL, &state);
@@ -366,13 +365,10 @@ mark_heap(GC_word *addr, struct GC_ms_entry
*mark_stack_ptr,
struct gc_heap *heap = (struct gc_heap*) addr;
- // If this heap is on a freelist... well probably we are screwed, BDW
- // isn't really made to do multiple heaps in a process. But still, in
- // this case, the first word is the freelist and the rest are null.
- if (heap->freelist) {
- bdw_mark_edge(gc_edge(addr), NULL, &state);
+ // If this heap is not __the_bdw_gc_heap, either it is on a freelist, or the
+ // heap object is still under construction. In either case, ignore it.
+ if (heap != __the_bdw_gc_heap)
return state.mark_stack_ptr;
- }
if (heap->roots)
gc_trace_heap_roots(heap->roots, bdw_mark_edge, heap, &state);
@@ -397,9 +393,12 @@ mark_mutator(GC_word *addr, struct GC_ms_entry
*mark_stack_ptr,
struct gc_mutator *mut = (struct gc_mutator*) addr;
- // If this mutator is on a freelist, its first word will be a
- // freelist link and everything else will be NULL.
- if (!mut->heap) {
+ // A mutator is valid and initialized if its "heap" member points to
+ // __the_bdw_gc_heap. Otherwise it could be on a freelist, in which case its
+ // first word will be a possibly-null freelist link, or it could be under
+ // construction, or it could be exited already. In any case, mark the free
+ // list link and finish.
+ if (mut->heap != __the_bdw_gc_heap) {
bdw_mark_edge(gc_edge(addr), NULL, &state);
return state.mark_stack_ptr;
}
@@ -420,7 +419,6 @@ mark_mutator(GC_word *addr, struct GC_ms_entry
*mark_stack_ptr,
static inline struct gc_mutator *add_mutator(struct gc_heap *heap) {
struct gc_mutator *ret =
GC_generic_malloc(sizeof(struct gc_mutator), mutator_gc_kind);
- ret->heap = heap;
ret->event_listener_data =
heap->event_listener.mutator_added(heap->event_listener_data);
@@ -430,6 +428,7 @@ static inline struct gc_mutator *add_mutator(struct gc_heap
*heap) {
if (ret->next)
ret->next->prev = &ret->next;
heap->mutators = ret;
+ ret->heap = heap;
GC_alloc_unlock();
return ret;
