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py/gc: Split out running finalizers to a separate pass.

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Currently a finalizer may run and access memory which has already been
freed. (This happens mostly during gc_sweep_all() but could happen during
any garbage collection pass.)

Includes some speed improvement tweaks to skip empty FTB blocks. These help
compensate for the inherent slowdown of having to walk the heap twice.

Signed-off-by: Angus Gratton <angus@redyak.com.au>
This commit is contained in:
Angus Gratton
2024-12-04 10:53:08 +11:00
committed by Damien George
parent d642cce27a
commit 8a2ff2ca73
1 changed files with 43 additions and 24 deletions
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67
py/gc.c
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@@ -477,29 +477,20 @@ static void gc_deal_with_stack_overflow(void) {
}
}
static void gc_sweep(void) {
#if MICROPY_PY_GC_COLLECT_RETVAL
MP_STATE_MEM(gc_collected) = 0;
#endif
// free unmarked heads and their tails
int free_tail = 0;
#if MICROPY_GC_SPLIT_HEAP_AUTO
mp_state_mem_area_t *prev_area = NULL;
#endif
for (mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
size_t end_block = area->gc_alloc_table_byte_len * BLOCKS_PER_ATB;
if (area->gc_last_used_block < end_block) {
end_block = area->gc_last_used_block + 1;
}
size_t last_used_block = 0;
for (size_t block = 0; block < end_block; block++) {
MICROPY_GC_HOOK_LOOP(block);
switch (ATB_GET_KIND(area, block)) {
case AT_HEAD:
#if MICROPY_ENABLE_FINALISER
if (FTB_GET(area, block)) {
// Run finalisers for all to-be-freed blocks
static void gc_sweep_run_finalisers(void) {
#if MICROPY_ENABLE_FINALISER
for (const mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
assert(area->gc_last_used_block <= area->gc_alloc_table_byte_len * BLOCKS_PER_ATB);
// Small speed optimisation: skip over empty FTB blocks
size_t ftb_end = area->gc_last_used_block / BLOCKS_PER_FTB; // index is inclusive
for (size_t ftb_idx = 0; ftb_idx <= ftb_end; ftb_idx++) {
byte ftb = area->gc_finaliser_table_start[ftb_idx];
size_t block = ftb_idx * BLOCKS_PER_FTB;
while (ftb) {
MICROPY_GC_HOOK_LOOP(block);
if (ftb & 1) { // FTB_GET(area, block) shortcut
if (ATB_GET_KIND(area, block) == AT_HEAD) {
mp_obj_base_t *obj = (mp_obj_base_t *)PTR_FROM_BLOCK(area, block);
if (obj->type != NULL) {
// if the object has a type then see if it has a __del__ method
@@ -519,7 +510,35 @@ static void gc_sweep(void) {
// clear finaliser flag
FTB_CLEAR(area, block);
}
#endif
}
ftb >>= 1;
block++;
}
}
}
#endif // MICROPY_ENABLE_FINALISER
}
static void gc_sweep(void) {
#if MICROPY_PY_GC_COLLECT_RETVAL
MP_STATE_MEM(gc_collected) = 0;
#endif
// free unmarked heads and their tails
int free_tail = 0;
#if MICROPY_GC_SPLIT_HEAP_AUTO
mp_state_mem_area_t *prev_area = NULL;
#endif
gc_sweep_run_finalisers();
for (mp_state_mem_area_t *area = &MP_STATE_MEM(area); area != NULL; area = NEXT_AREA(area)) {
size_t last_used_block = 0;
assert(area->gc_last_used_block <= area->gc_alloc_table_byte_len * BLOCKS_PER_ATB);
for (size_t block = 0; block <= area->gc_last_used_block; block++) {
MICROPY_GC_HOOK_LOOP(block);
switch (ATB_GET_KIND(area, block)) {
case AT_HEAD:
free_tail = 1;
DEBUG_printf("gc_sweep(%p)\n", (void *)PTR_FROM_BLOCK(area, block));
#if MICROPY_PY_GC_COLLECT_RETVAL