Race condition inside PyThread_release_lock should have been fixed on
both CPython/darwin and PyPy/darwin:

    https://github.com/python/cpython/commit/c5abd63e94fc
    https://bitbucket.org/pypy/pypy/commits/6cd7a0d1a940
    https://bitbucket.org/pypy/pypy/commits/a9d36d6af872

The bug is explained here:

    https://bugs.python.org/issue38106
    https://bitbucket.org/pypy/pypy/issues/3072

The following commits added tests for the bug on Pygolang side:

    34b7a1f4 (golang: Expose Sema and Mutex as public Python and Cython/nogil API)
    5142460d (libgolang/thread: Add links to upstream PyThread_release_lock bug)