Function GC_do_blocking 

pub unsafe extern "C" fn GC_do_blocking(
    arg1: GC_fn_type,
    arg2: *mut c_void,
) -> *mut c_void

Wrapper for functions that are likely to block (or, at least, do not allocate garbage-collected memory and/or manipulate pointers to the garbage-collected heap) for an appreciable length of time. While fn is running, the collector is said to be in the “inactive” state for the current thread (this means that the thread is not suspended and the thread’s stack frames “belonging” to the functions in the “inactive” state are not scanned during garbage collections). It is assumed that the collector is already initialized and the current thread is registered. It is allowed for fn to call GC_call_with_gc_active() (even recursively), thus temporarily toggling the collector’s state back to “active”. The latter technique might be used to make stack scanning more precise (i.e. scan only stack frames of functions that allocate garbage-collected memory and/or manipulate pointers to the garbage-collected heap). Acquires the allocator lock in the reader mode (but fn is called not holding it).