Python wrapper for PortAudio's ring buffer

The ring buffer functionality is typically not included in binary distributions of PortAudio, therefore most Python wrappers don't include it, either.

The pa_ringbuffer module provides only a Python wrapper, the actual PortAudio ring buffer code has to be compiled separately, see Usage. It can be used on any Python version where CFFI is available.

This module is designed to be used together with the sounddevice module (it might work with other modules, too) for non-blocking transfer of data between the main Python program and an audio callback function which is implemented in C or some other compiled language.

Usage

This module is not meant to be used on its own, it is only useful in cooperation with another Python module using CFFI. For an example, have a look at https://github.com/spatialaudio/python-rtmixer.

You can get the Python code from PyPI, for example in your setup.py file (in the following example, your module would be called mycffimodule):

from setuptools import setup

setup(
    name=...,
    version=...,
    author=...,
    ...,
    cffi_modules=['mycffimodule_build.py:ffibuilder'],
    setup_requires=['CFFI', 'pa_ringbuffer'],
    install_requires=['pa_ringbuffer'],
    ...,
)

Alternatively, you can just copy the file src/pa_ringbuffer.py to your own source directory and import it from there.

You can build your own CFFI module like described in http://cffi.readthedocs.io/en/latest/cdef.html, just adding a few more bits to your mycffimodule_build.py:

from cffi import FFI
import pa_ringbuffer

ffibuilder = FFI()
ffibuilder.cdef(pa_ringbuffer.cdef())
ffibuilder.cdef("""

/* my own declarations */

""")
ffibuilder.set_source(
    '_mycffimodule',
    '/* my implementation */',
    sources=['portaudio/src/common/pa_ringbuffer.c'],
)

if __name__ == '__main__':
    ffibuilder.compile(verbose=True)

Note that the following files must be available to the compiler:

• https://github.com/PortAudio/portaudio/blob/master/src/common/pa_ringbuffer.c
• https://github.com/PortAudio/portaudio/blob/master/src/common/pa_ringbuffer.h
• https://github.com/PortAudio/portaudio/blob/master/src/common/pa_memorybarrier.h

For your own C code, you might need some definitions from the main PortAudio header:

• https://github.com/PortAudio/portaudio/blob/master/include/portaudio.h

Once you have compiled your extension module (with the help of CFFI), you can use something like this in your own module to get access to the RingBuffer class:

import pa_ringbuffer
from _mycffimodule import ffi, lib

RingBuffer = pa_ringbuffer.init(ffi, lib)

API Reference

There are only two functions:

pa_ringbuffer.cdef()

This function returns a string containing C declarations from the file pa_ringbuffer.h, which can be used as argument to CFFI's cdef() function (see Usage above). Note that the returned declarations are slightly different when called on a macOS/Darwin system.

pa_ringbuffer.init(ffi, lib)

This function returns the RingBuffer class which is associated with the CFFI instance given by ffi and lib.

Creating the Documentation

The documentation of the RingBuffer class is not available separately. If you are using Sphinx, you can seamlessly include the documentation of the RingBuffer class with your own documentation. An example for this can be found at https://github.com/spatialaudio/python-rtmixer, the generated documentation is available at https://python-rtmixer.readthedocs.io/api.html#rtmixer.RingBuffer.

You'll need to have the autodoc extension activated in your conf.py:

extensions = [
    ...,
    'sphinx.ext.autodoc',
    ...,
]

And somewhere within your module documentation, you should add this:

.. autoclass:: RingBuffer
   :inherited-members:

Before that, you might have to use the currentmodule directive to select your own module. Using automodule should also do.

If you want to use Sphinx's nitpicky setting, you'll have to add a few things to nitpick_ignore:

nitpicky = True
nitpick_ignore = [
    ('py:class', 'optional'),
    ('py:class', 'buffer'),
    ('py:class', 'CData pointer'),
]