Help needed to extend the core.thread

[Heromyth via Digitalmars-d-learn]

I want make some extensions to Thread in core.thread and wan. So 
I copy the whole of core.thread to another module named 
myext.thread.

Here are two errors occurred:
1)When building this module
In function `_D4myext6thread6Thread9termLocksFNiZv':
/home/dlang/UnitTest/source/myext/thread.d:1723: undefined 
reference to `_D4core4sync5mutex5Mutex6__dtorMFNiNeZv'

2)When running a simple demo with empty main().
Program exited with code -11

It seems it is bad idea to do so.
Maybe it's better to extend core.thread.Thread by inheriting it.
Am I right? Thanks!