This is xnu-8019. See this file in:
Directory listing for xnu-8019//libkern/os
Makefile
atomic.h
atomic_private.h
atomic_private_arch.h
atomic_private_impl.h
base.h
base_private.h
cpp_util.h
firehose.h
hash.h
internal.c
log.c
log.h
log_encode.c
log_encode.h
log_encode_types.h
log_internal.h
log_mem.c
log_mem.h
log_private.h
log_queue.c
log_queue.h
object.c
object.h
overflow.h
ptrtools.h
reason_private.h
refcnt.c
refcnt.h
refcnt_internal.h
trace.h
trace_internal.h