Distribute the CFFI ring implementation in the wheels?

[jamadden]

This is mostly a problem for PyPy users on Windows (who probably don't have compilers).

We should be able to do this with this snippet in setup.py (having made sure to install CFFI and zope.interface first; the zope.interface requirement could be dropped with some refactoring):

try:
    import cffi
    import persistent.ring
except ImportError:
    pass
else:
    ext_modules.append(persistent.ring.ffi.verifier.get_extension())

That should work back to PyPy 2.5.1 or so, which is the version on Travis.

Now the second half of this is that we don't distribute PyPy wheels, so to meet the stated purpose we'd also need to do that (at least on Windows)

[jamadden]

Full disclosure: I'm using the Ring implementation in RelStorage (I know it's documented as not for external use---I wrote those docs :) and the CFFIRing is much faster than the DequeRing on CPython. It would be nice to piggyback on the existing Appveyor setup and such of persistent so that I don't have to set all that up for RelStorage and can keep uploading just a single universal wheel.

[tseaver]

Importing the module-to-be-installed in setup.py feels icky to me. Can we use something from @dstufft's CFFI blog post?

Also, for Windows PyPy users, why would they want the CFFI ring, if the deque version is only faster for CPython?

[jamadden]

On Aug 10, 2016, at 12:27, Tres Seaver notifications@github.com wrote:

Importing the module-to-be-installed in setup.py feels icky to me. Can we use something from @dstufft's CFFI blog post?

I agree it's ugly. But it's the only way to work with older CFFI versions, like the version shipped with PyPy on Travis. To use the cffi_modules keyword you need at least PyPy 2.6 IIRC. I went through the same pain for gevent.

[jamadden]

On Aug 10, 2016, at 12:27, Tres Seaver notifications@github.com wrote:

Also, for Windows PyPy users, why would they want the CFFI ring, if the deque version is only faster for CPython?

The CFFI ring is faster than the deque ring everywhere, as far as I can remember. But currently PyPy windows users (or CPython users that define PURE_PYTHON, for that matter) will get the deque ring unless they're set up to compile extension modules.

But that only matters for users of the pure-python persistent implementation, because the C implementation includes its own ring (that the CFFI implementation uses).

[jamadden]

In zodb/relstorage#128, I realized it was possible to support both the old and new style of CFFI building at the same time. And then, when I needed features that PyPy 2.5 doesn't support, I realized that (a) nobody is using PyPy 2.5, given the current version is 5.4 and much faster; and (b) it's pretty trivial and doesn't hurt Travis test times to install an updated PyPy on Travis.

So we could do that and it might be a good thing.

But my own need for this has gone away. See #45.