Function GC_unregister_my_thread 

pub unsafe extern "C" fn GC_unregister_my_thread() -> c_int

Unregister the current thread. Only an explicitly registered thread (i.e. for which GC_register_my_thread() returns GC_SUCCESS) is allowed (and required) to call this function. (As a special exception, it is also allowed to once unregister the main thread.) The thread may no longer allocate garbage-collected memory or manipulate pointers to the garbage-collected heap after making this call. Specifically, if it wants to return or otherwise communicate a pointer to the garbage-collected heap to another thread, it must do this before calling GC_unregister_my_thread, most probably by saving it in a global data structure. Must not be called inside a GC callback function (except for GC_call_with_stack_base() one). Always returns GC_SUCCESS.