Function GC_get_avg_stopped_mark_time_ns 

pub unsafe extern "C" fn GC_get_avg_stopped_mark_time_ns() -> c_ulong

Get the average time spent in all mark phases with the world stopped. The average value is computed since the start of the performance measurements (or right since the collector initialization if the collector logging is enabled). The result is in nanoseconds. The function acquires the allocator lock (in the reader mode) to avoid data race. Defined only if the library has been compiled without NO_CLOCK macro defined.