The main stated reason for untraceable locks was a bug in Python 2.5,
fixed in all recent versions, so that shouldn't be a concern.

The semaphore takes some careful lock management to come close to
duplicating the thread-safety inherent in Cython's compiled methods.

'pypy -m timeit -s "import g.l.Semaphore; s=Semaphore()"' 's.acquire();s.releas()':

With Cython compiled semaphore: 5usec
With pure-python sempahore: 0.004usec
With pure-python-but-locked semaphore: 0.178usec
Cython on CPython: 0.141usec

Total test runtime is unchanged.