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Fix bug in which we could forget to mark stopping mutators

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Separately track total mutator count, paused mutators, and inactive
mutators.  Paused mutators need to mark their roots before stopping.  We
had a bug whereby a paused mutator would not wake up before the next
collection, which resulted in that mutator's roots not being marked.
Fix by resetting paused mutator count to 0 after collection, requiring
those mutators to sync up again.
This commit is contained in:
Andy Wingo 2023-11-10 15:09:10 +01:00
parent adaffab3da
commit 3ce75b2bad
1 changed files with 27 additions and 26 deletions
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49
src/whippet.c
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@ -303,13 +303,14 @@ struct gc_heap {
struct gc_pending_ephemerons *pending_ephemerons;
enum gc_collection_kind gc_kind;
int multithreaded;
size_t active_mutator_count;
size_t mutator_count;
size_t paused_mutator_count;
size_t inactive_mutator_count;
struct gc_heap_roots *roots;
struct gc_mutator *mutator_trace_list;
long count;
uint8_t last_collection_was_minor;
struct gc_mutator *deactivated_mutators;
struct gc_mutator *inactive_mutators;
struct tracer tracer;
double fragmentation_low_threshold;
double fragmentation_high_threshold;
@ -852,6 +853,12 @@ static inline void heap_unlock(struct gc_heap *heap) {
pthread_mutex_unlock(&heap->lock);
}
// with heap lock
static inline int all_mutators_stopped(struct gc_heap *heap) {
return heap->mutator_count ==
heap->paused_mutator_count + heap->inactive_mutator_count;
}
static void add_mutator(struct gc_heap *heap, struct gc_mutator *mut) {
mut->heap = heap;
mut->event_listener_data =
@ -863,7 +870,6 @@ static void add_mutator(struct gc_heap *heap, struct gc_mutator *mut) {
pthread_cond_wait(&heap->mutator_cond, &heap->lock);
if (heap->mutator_count == 1)
heap->multithreaded = 1;
heap->active_mutator_count++;
heap->mutator_count++;
heap_unlock(heap);
}
@ -872,11 +878,10 @@ static void remove_mutator(struct gc_heap *heap, struct gc_mutator *mut) {
MUTATOR_EVENT(mut, mutator_removed);
mut->heap = NULL;
heap_lock(heap);
heap->active_mutator_count--;
heap->mutator_count--;
// We have no roots. If there is a GC stop currently in progress,
// maybe tell the controller it can continue.
if (mutators_are_stopping(heap) && heap->active_mutator_count == 0)
if (mutators_are_stopping(heap) && all_mutators_stopped(heap))
pthread_cond_signal(&heap->collector_cond);
heap_unlock(heap);
}
@ -888,8 +893,8 @@ static void request_mutators_to_stop(struct gc_heap *heap) {
static void allow_mutators_to_continue(struct gc_heap *heap) {
GC_ASSERT(mutators_are_stopping(heap));
GC_ASSERT(heap->active_mutator_count == 0);
heap->active_mutator_count++;
GC_ASSERT(all_mutators_stopped(heap));
heap->paused_mutator_count = 0;
atomic_store_explicit(&heap->collecting, 0, memory_order_relaxed);
GC_ASSERT(!mutators_are_stopping(heap));
pthread_cond_broadcast(&heap->mutator_cond);
@ -1291,8 +1296,8 @@ static void release_stopping_mutator_roots(struct gc_mutator *mut) {
}
static void wait_for_mutators_to_stop(struct gc_heap *heap) {
heap->active_mutator_count--;
while (heap->active_mutator_count)
heap->paused_mutator_count++;
while (!all_mutators_stopped(heap))
pthread_cond_wait(&heap->collector_cond, &heap->lock);
}
@ -1307,7 +1312,7 @@ static void trace_mutator_conservative_roots_after_stop(struct gc_heap *heap) {
mut = mut->next)
trace_mutator_conservative_roots_with_lock(mut);
for (struct gc_mutator *mut = heap->deactivated_mutators;
for (struct gc_mutator *mut = heap->inactive_mutators;
mut;
mut = mut->next)
trace_mutator_conservative_roots_with_lock(mut);
@ -1331,7 +1336,7 @@ static void trace_mutator_roots_after_stop(struct gc_heap *heap) {
}
atomic_store(&heap->mutator_trace_list, NULL);
for (struct gc_mutator *mut = heap->deactivated_mutators; mut; mut = mut->next) {
for (struct gc_mutator *mut = heap->inactive_mutators; mut; mut = mut->next) {
finish_sweeping_in_block(mut);
trace_mutator_roots_with_lock(mut);
}
@ -1424,11 +1429,11 @@ pause_mutator_for_collection(struct gc_heap *heap,
static enum gc_collection_kind
pause_mutator_for_collection(struct gc_heap *heap, struct gc_mutator *mut) {
GC_ASSERT(mutators_are_stopping(heap));
GC_ASSERT(heap->active_mutator_count);
GC_ASSERT(!all_mutators_stopped(heap));
MUTATOR_EVENT(mut, mutator_stopped);
heap->active_mutator_count--;
heap->paused_mutator_count++;
enum gc_collection_kind collection_kind = heap->gc_kind;
if (heap->active_mutator_count == 0)
if (all_mutators_stopped(heap))
pthread_cond_signal(&heap->collector_cond);
// Go to sleep and wake up when the collector is done. Note,
@ -1444,7 +1449,6 @@ pause_mutator_for_collection(struct gc_heap *heap, struct gc_mutator *mut) {
while (mutators_are_stopping(heap) && heap->count == epoch);
MUTATOR_EVENT(mut, mutator_restarted);
heap->active_mutator_count++;
return collection_kind;
}
@ -1588,8 +1592,6 @@ determine_collection_kind(struct gc_heap *heap,
ssize_t pending = atomic_load_explicit(&mark_space->pending_unavailable_bytes,
memory_order_acquire);
DEBUG("hiiiiii\n");
if (heap->count == 0) {
DEBUG("first collection is always major\n");
gc_kind = GC_COLLECTION_MAJOR;
@ -1920,7 +1922,6 @@ static void collect(struct gc_mutator *mut,
heap_reset_large_object_pages(heap, lospace->live_pages_at_last_collection);
HEAP_EVENT(heap, restarting_mutators);
allow_mutators_to_continue(heap);
DEBUG("collect done\n");
}
static int sweep_byte(uint8_t *loc, uintptr_t sweep_mask) {
@ -2485,11 +2486,11 @@ void gc_finish_for_thread(struct gc_mutator *mut) {
static void deactivate_mutator(struct gc_heap *heap, struct gc_mutator *mut) {
GC_ASSERT(mut->next == NULL);
heap_lock(heap);
mut->next = heap->deactivated_mutators;
heap->deactivated_mutators = mut;
heap->active_mutator_count--;
mut->next = heap->inactive_mutators;
heap->inactive_mutators = mut;
heap->inactive_mutator_count++;
gc_stack_capture_hot(&mut->stack);
if (!heap->active_mutator_count && mutators_are_stopping(heap))
if (all_mutators_stopped(heap))
pthread_cond_signal(&heap->collector_cond);
heap_unlock(heap);
}
@ -2498,12 +2499,12 @@ static void reactivate_mutator(struct gc_heap *heap, struct gc_mutator *mut) {
heap_lock(heap);
while (mutators_are_stopping(heap))
pthread_cond_wait(&heap->mutator_cond, &heap->lock);
struct gc_mutator **prev = &heap->deactivated_mutators;
struct gc_mutator **prev = &heap->inactive_mutators;
while (*prev != mut)
prev = &(*prev)->next;
*prev = mut->next;
mut->next = NULL;
heap->active_mutator_count++;
heap->inactive_mutator_count--;
heap_unlock(heap);
}