Static GC_non_gc_bytes 

pub unsafe static mut GC_non_gc_bytes: GC_word

Bytes not considered candidates for collection. Used only to control scheduling of collections. Updated by GC_malloc_uncollectable(), GC_free() and friends. Wizards only. The setter and the getter are unsynchronized, so GC_call_with_alloc_lock() (GC_call_with_reader_lock() in case of the getter) is required to avoid data race (if the value is modified after the collector is put into the multi-threaded mode).