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Experimental change to fix GC crashes

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I think the real problem may be that we mark globals before waiting for the mutators to transition to the new Mark color. If we wait until after a minor gc to update the mark color, there is a window where the mutator may sweep, and this is after globals have been marked. So the newly marked objects may be accidentally freed by sweep!
This commit is contained in:
Justin Ethier 2018-07-14 21:23:28 -04:00
parent 5216131309
commit 1343490c9b
1 changed files with 4 additions and 4 deletions
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8
gc.c
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@ -1562,7 +1562,7 @@ gc_heap *gc_sweep(gc_heap * h, int heap_type, gc_thread_data *thd)
gc_heap *orig_heap_ptr = h;
#endif
gc_heap *rv = h;
int markColor = ck_pr_load_8(&gc_color_mark);
//int markColor = ck_pr_load_8(&gc_color_mark);
//h->next_free = h;
h->last_alloc_size = 0;
@ -1620,7 +1620,7 @@ gc_heap *gc_sweep(gc_heap * h, int heap_type, gc_thread_data *thd)
}
#endif
if (mark(p) != markColor &&
if (//mark(p) != markColor &&
mark(p) != thd->gc_alloc_color &&
mark(p) != thd->gc_trace_color) { //gc_color_clear)
#if GC_DEBUG_VERBOSE
@ -1629,7 +1629,7 @@ gc_heap *gc_sweep(gc_heap * h, int heap_type, gc_thread_data *thd)
mark(p),
thd->gc_alloc_color, thd->gc_trace_color);
#endif
mark(p) = gc_color_blue; // Needed?
//mark(p) = gc_color_blue; // Needed?
if (type_of(p) == mutex_tag) {
#if GC_DEBUG_VERBOSE
fprintf(stderr, "pthread_mutex_destroy from sweep\n");
@ -2516,8 +2516,8 @@ void gc_collector()
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - after post_handshake async\n");
#endif
gc_request_mark_globals();
gc_wait_handshake();
gc_request_mark_globals(); // Wait until mutators have new mark color
#if GC_DEBUG_TRACE
fprintf(stderr, "DEBUG - after wait_handshake async\n");
#endif