Support multiple architectures

[mansourmoufid]

Hello,

At the moment, briefcase installs all Python packages into a single directory (app_packages). This works great for pure-Python packages. It also works for modules compiled for a single architecture.

It would be nice to support multiple architectures (e.g. armeabi-v7a and arm64-v8a on Android). I can think of two possible solutions. First, architecture-specific package directories. Second, architecture-specific filename extensions. Which is better?

Edit: I forgot to mention... The first requires changes to briefcase and briefcase-android-gradle-template; the second requires changes to briefcase and Python-Android-support, so I opened the issue here for discussion.

Solution 1

TODO

Solution 2

The extension of Python modules is set by the configure script according to the variable SOABI:

# ABI version string for Python extension modules.  This appears between the
# periods in shared library file names, e.g. foo.<SOABI>.so.  It is calculated
# from the following attributes which affect the ABI of this Python build (in
# this order):
#
# * The Python implementation (always 'cpython-' for us)
# * The major and minor version numbers
# * --with-pydebug (adds a 'd')
#
# Thus for example, Python 3.2 built with wide unicode, pydebug, and pymalloc,
# would get a shared library ABI version tag of 'cpython-32dmu' and shared
# libraries would be named 'foo.cpython-32dmu.so'.
#
# In Python 3.2 and older, --with-wide-unicode added a 'u' flag.
# In Python 3.7 and older, --with-pymalloc added a 'm' flag.
AC_SUBST(SOABI)
AC_MSG_CHECKING(ABIFLAGS)
AC_MSG_RESULT($ABIFLAGS)
AC_MSG_CHECKING(SOABI)
SOABI='cpython-'`echo $VERSION | tr -d .`${ABIFLAGS}${PLATFORM_TRIPLET:+-$PLATFORM_TRIPLET}
AC_MSG_RESULT($SOABI)

This value is then accessible at run-time with sysconfig.get_config_var('EXT_SUFFIX').

The distutils module (and setuptools) uses EXT_SUFFIX when compiling modules (the build_ext command):

    def get_ext_filename(self, ext_name):
        r"""Convert the name of an extension (eg. "foo.bar") into the name
        of the file from which it will be loaded (eg. "foo/bar.so", or
        "foo\bar.pyd").
        """
        from distutils.sysconfig import get_config_var
        ext_path = ext_name.split('.')
        ext_suffix = get_config_var('EXT_SUFFIX')
        return os.path.join(*ext_path) + ext_suffix

So if we set SOABI during configure to the Android ABI, say "arm64-v8a", then EXT_SUFFIX is ".arm64-v8a.so". Then distutils and setuptools can be patched to read EXT_SUFFIX from an environment variable rather than the host Python's sysconfig.

Then, hopefully, briefcase would just work with multiple architectures.

[paulproteus]

Hi @eliteraspberries !

I think that the directories approach is the better one. The reason is that https://developer.android.com/ndk/guides/abis#native-code-in-app-packages indicates that Android and the Play Store have some tooling that assumes a directory-based layout.

Let me know what you think. I haven't done any substantial work on Python-Android-support in a year-ish, so my understanding may be inaccurate in pieces.

[mansourmoufid]

Ah yes, that does make more sense. Now that I read more of the source, it's also the simpler solution. It might even be possible to implement this with only changes to briefcase, and maybe a line or two in briefcase-android-gradle-template.

[mansourmoufid]

OK solution 1 works. See: beeware/briefcase#647 (comment)