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Ractor-safe rb_objspace_reachable_objects_from
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rb_objspace_reachable_objects_from(obj) is used to traverse all
reachable objects from obj. This function modify objspace but it
is not ractor-safe (thread-safe). This patch fix the problem.

Strategy:
(1) call GC mark process during_gc
(2) call Ractor-local custom mark func when !during_gc
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@ko1
ko1 committed Oct 21, 2020
1 parent 4640c4e commit b59077e
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Showing 2 changed files with 88 additions and 77 deletions.
158 changes: 82 additions & 76 deletions gc.c
View file
Expand Up @@ -690,11 +690,6 @@ typedef struct rb_objspace {
rb_atomic_t finalizing;
} atomic_flags;

struct mark_func_data_struct {
void *data;
void (*mark_func)(VALUE v, void *data);
} *mark_func_data;

mark_stack_t mark_stack;
size_t marked_slots;

Expand Down Expand Up @@ -1072,12 +1067,6 @@ static inline void gc_prof_set_heap_info(rb_objspace_t *);
PRINTF_ARGS(static void gc_report_body(int level, rb_objspace_t *objspace, const char *fmt, ...), 3, 4);
static const char *obj_info(VALUE obj);

#define PUSH_MARK_FUNC_DATA(v) do { \
struct mark_func_data_struct *prev_mark_func_data = objspace->mark_func_data; \
objspace->mark_func_data = (v);

#define POP_MARK_FUNC_DATA() objspace->mark_func_data = prev_mark_func_data;} while (0)

/*
* 1 - TSC (H/W Time Stamp Counter)
* 2 - getrusage
Expand Down Expand Up @@ -5138,7 +5127,7 @@ mark_hash(rb_objspace_t *objspace, VALUE hash)
}

if (RHASH_AR_TABLE_P(hash)) {
if (objspace->mark_func_data == NULL && RHASH_TRANSIENT_P(hash)) {
if (LIKELY(during_gc) && RHASH_TRANSIENT_P(hash)) {
rb_transient_heap_mark(hash, RHASH_AR_TABLE(hash));
}
}
Expand Down Expand Up @@ -5453,11 +5442,12 @@ gc_aging(rb_objspace_t *objspace, VALUE obj)
}

NOINLINE(static void gc_mark_ptr(rb_objspace_t *objspace, VALUE obj));
static void reachable_objects_from_callback(VALUE obj);

static void
gc_mark_ptr(rb_objspace_t *objspace, VALUE obj)
{
if (LIKELY(objspace->mark_func_data == NULL)) {
if (LIKELY(during_gc)) {
rgengc_check_relation(objspace, obj);
if (!gc_mark_set(objspace, obj)) return; /* already marked */
if (RB_TYPE_P(obj, T_NONE)) {
Expand All @@ -5468,7 +5458,7 @@ gc_mark_ptr(rb_objspace_t *objspace, VALUE obj)
gc_grey(objspace, obj);
}
else {
objspace->mark_func_data->mark_func(obj, objspace->mark_func_data->data);
reachable_objects_from_callback(obj);
}
}

Expand All @@ -5477,7 +5467,7 @@ gc_pin(rb_objspace_t *objspace, VALUE obj)
{
GC_ASSERT(is_markable_object(objspace, obj));
if (UNLIKELY(objspace->flags.during_compacting)) {
if (LIKELY(objspace->mark_func_data == NULL)) {
if (LIKELY(during_gc)) {
MARK_IN_BITMAP(GET_HEAP_PINNED_BITS(obj), obj);
}
}
Expand Down Expand Up @@ -5678,7 +5668,7 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
gc_mark(objspace, ptr[i]);
}

if (objspace->mark_func_data == NULL) {
if (LIKELY(during_gc)) {
if (!FL_TEST_RAW(obj, RARRAY_EMBED_FLAG) &&
RARRAY_TRANSIENT_P(obj)) {
rb_transient_heap_mark(obj, ptr);
Expand Down Expand Up @@ -5719,7 +5709,7 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
gc_mark(objspace, ptr[i]);
}

if (objspace->mark_func_data == NULL &&
if (LIKELY(during_gc) &&
ROBJ_TRANSIENT_P(obj)) {
rb_transient_heap_mark(obj, ptr);
}
Expand Down Expand Up @@ -5770,7 +5760,7 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
gc_mark(objspace, ptr[i]);
}

if (objspace->mark_func_data == NULL &&
if (LIKELY(during_gc) &&
RSTRUCT_TRANSIENT_P(obj)) {
rb_transient_heap_mark(obj, ptr);
}
Expand Down Expand Up @@ -6429,7 +6419,7 @@ gc_verify_internal_consistency_m(VALUE dummy)
}

static void
gc_verify_internal_consistency(rb_objspace_t *objspace)
gc_verify_internal_consistency_(rb_objspace_t *objspace)
{
struct verify_internal_consistency_struct data = {0};

Expand Down Expand Up @@ -6502,6 +6492,17 @@ gc_verify_internal_consistency(rb_objspace_t *objspace)
gc_report(5, objspace, "gc_verify_internal_consistency: OK\n");
}

static void
gc_verify_internal_consistency(rb_objspace_t *objspace)
{
unsigned int prev_during_gc = during_gc;
during_gc = FALSE; // stop gc here
{
gc_verify_internal_consistency_(objspace);
}
during_gc = prev_during_gc;
}

void
rb_gc_verify_internal_consistency(void)
{
Expand Down Expand Up @@ -6780,35 +6781,31 @@ gc_marks_continue(rb_objspace_t *objspace, rb_heap_t *heap)
unsigned int lock_lev;
gc_enter(objspace, "marks_continue", &lock_lev);

PUSH_MARK_FUNC_DATA(NULL);
{
int slots = 0;
const char *from;
int slots = 0;
const char *from;

if (heap->pooled_pages) {
while (heap->pooled_pages && slots < HEAP_PAGE_OBJ_LIMIT) {
struct heap_page *page = heap_move_pooled_pages_to_free_pages(heap);
slots += page->free_slots;
}
from = "pooled-pages";
}
else if (heap_increment(objspace, heap)) {
slots = heap->free_pages->free_slots;
from = "incremented-pages";
}
if (heap->pooled_pages) {
while (heap->pooled_pages && slots < HEAP_PAGE_OBJ_LIMIT) {
struct heap_page *page = heap_move_pooled_pages_to_free_pages(heap);
slots += page->free_slots;
}
from = "pooled-pages";
}
else if (heap_increment(objspace, heap)) {
slots = heap->free_pages->free_slots;
from = "incremented-pages";
}

if (slots > 0) {
gc_report(2, objspace, "gc_marks_continue: provide %d slots from %s.\n",
slots, from);
gc_marks_step(objspace, objspace->rincgc.step_slots);
}
else {
gc_report(2, objspace, "gc_marks_continue: no more pooled pages (stack depth: %"PRIdSIZE").\n",
mark_stack_size(&objspace->mark_stack));
gc_marks_rest(objspace);
}
if (slots > 0) {
gc_report(2, objspace, "gc_marks_continue: provide %d slots from %s.\n",
slots, from);
gc_marks_step(objspace, objspace->rincgc.step_slots);
}
else {
gc_report(2, objspace, "gc_marks_continue: no more pooled pages (stack depth: %"PRIdSIZE").\n",
mark_stack_size(&objspace->mark_stack));
gc_marks_rest(objspace);
}
POP_MARK_FUNC_DATA();

gc_exit(objspace, "marks_continue", &lock_lev);
#endif
Expand All @@ -6819,23 +6816,19 @@ gc_marks(rb_objspace_t *objspace, int full_mark)
{
gc_prof_mark_timer_start(objspace);

PUSH_MARK_FUNC_DATA(NULL);
{
/* setup marking */
/* setup marking */

gc_marks_start(objspace, full_mark);
if (!is_incremental_marking(objspace)) {
gc_marks_rest(objspace);
}
gc_marks_start(objspace, full_mark);
if (!is_incremental_marking(objspace)) {
gc_marks_rest(objspace);
}

#if RGENGC_PROFILE > 0
if (gc_prof_record(objspace)) {
gc_profile_record *record = gc_prof_record(objspace);
record->old_objects = objspace->rgengc.old_objects;
}
#endif
if (gc_prof_record(objspace)) {
gc_profile_record *record = gc_prof_record(objspace);
record->old_objects = objspace->rgengc.old_objects;
}
POP_MARK_FUNC_DATA();
#endif
gc_prof_mark_timer_stop(objspace);
}

Expand Down Expand Up @@ -7677,10 +7670,8 @@ gc_rest(rb_objspace_t *objspace)
if (RGENGC_CHECK_MODE >= 2) gc_verify_internal_consistency(objspace);

if (is_incremental_marking(objspace)) {
PUSH_MARK_FUNC_DATA(NULL);
gc_marks_rest(objspace);
POP_MARK_FUNC_DATA();
}
gc_marks_rest(objspace);
}
if (is_lazy_sweeping(heap_eden)) {
gc_sweep_rest(objspace);
}
Expand Down Expand Up @@ -9805,18 +9796,30 @@ ruby_gc_set_params(void)
#endif
}

static void
reachable_objects_from_callback(VALUE obj)
{
rb_ractor_t *cr = GET_RACTOR();
cr->mfd->mark_func(obj, cr->mfd->data);
}

void
rb_objspace_reachable_objects_from(VALUE obj, void (func)(VALUE, void *), void *data)
{
rb_objspace_t *objspace = &rb_objspace;

if (during_gc) rb_bug("rb_objspace_reachable_objects_from() is not supported while during_gc == true");

if (is_markable_object(objspace, obj)) {
struct mark_func_data_struct mfd;
mfd.mark_func = func;
mfd.data = data;
PUSH_MARK_FUNC_DATA(&mfd);
rb_ractor_t *cr = GET_RACTOR();
struct gc_mark_func_data_struct mfd = {
.mark_func = func,
.data = data,
}, *prev_mfd = cr->mfd;

cr->mfd = &mfd;
gc_mark_children(objspace, obj);
POP_MARK_FUNC_DATA();
cr->mfd = prev_mfd;
}
}

Expand All @@ -9843,18 +9846,21 @@ rb_objspace_reachable_objects_from_root(void (func)(const char *category, VALUE,
static void
objspace_reachable_objects_from_root(rb_objspace_t *objspace, void (func)(const char *category, VALUE, void *), void *passing_data)
{
struct root_objects_data data;
struct mark_func_data_struct mfd;

data.func = func;
data.data = passing_data;
if (during_gc) rb_bug("objspace_reachable_objects_from_root() is not supported while during_gc == true");

mfd.mark_func = root_objects_from;
mfd.data = &data;
rb_ractor_t *cr = GET_RACTOR();
struct root_objects_data data = {
.func = func,
.data = passing_data,
};
struct gc_mark_func_data_struct mfd = {
.mark_func = root_objects_from,
.data = &data,
}, *prev_mfd = cr->mfd;

PUSH_MARK_FUNC_DATA(&mfd);
cr->mfd = &mfd;
gc_mark_roots(objspace, &data.category);
POP_MARK_FUNC_DATA();
cr->mfd = prev_mfd;
}

/*
Expand Down
7 changes: 6 additions & 1 deletion ractor.h
View file
Expand Up @@ -121,12 +121,17 @@ struct rb_ractor_struct {

struct list_node vmlr_node;


VALUE r_stdin;
VALUE r_stdout;
VALUE r_stderr;
VALUE verbose;
VALUE debug;

// gc.c rb_objspace_reachable_objects_from
struct gc_mark_func_data_struct {
void *data;
void (*mark_func)(VALUE v, void *data);
} *mfd;
}; // rb_ractor_t is defined in vm_core.h

rb_ractor_t *rb_ractor_main_alloc(void);
Expand Down

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