Thanks for the advices.

Antoine, maybe you could clarify the situation regarding buffer-locks
for me. In older versions of PEP 3118 the PyBUF_LOCK flag was still
present but it doesn't seem to have made it's way into the final draft.
Is it save to assume that a buffer-view will not change until release()
is called - for all types supporting the buffer protocol in py3k ??

I've done some testing and the overhead of releasing and re-locking the
GIL is definitely a performance problem when trying to hash many small
strings (doubled runtime for 100.000 times b'abc'). I've taken on
haypo's patch to release the GIL only when the buffer is larger than 10kb.