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pypy / pypy / doc / rffi.rst

David Malcolm 1e46012 

Dario Bertini 74b4a53 
David Malcolm 1e46012 

Dario Bertini 74b4a53 
David Malcolm 1e46012 

Dario Bertini 74b4a53 
David Malcolm 1e46012 

Foreign Function Interface for RPython


This document describes an FFI for RPython language, concentrating
on low-level backends like C. It describes
how to declare and call low-level (C) functions from RPython level.

Declaring low-level external function

Declaring external C function in RPython is easy, but one needs to
remember that low level functions eat `low level types`_ (like
lltype.Signed or lltype.Array) and memory management must be done
by hand. To declare a function, we write::

  from pypy.rpython.lltypesystem import rffi

  external_function = rffi.llexternal(name, args, result)


* name - a C-level name of a function (how it would be rendered)
* args - low level types of args
* result - low level type of a result

You can pass in additional information about C-level includes,
libraries and sources by passing in the optional ``compilation_info``

  from pypy.rpython.lltypesystem import rffi
  from pypy.translator.tool.cbuild import ExternalCompilationInfo

  info = ExternalCompilationInfo(includes=[], libraries=[])

  external_function = rffi.llexternal(
    name, args, result, compilation_info=info

See cbuild_ for more info on ExternalCompilationInfo.

.. _`low level types`: rtyper.html#low-level-type
.. _cbuild: https://bitbucket.org/pypy/pypy/src/tip/pypy/translator/tool/cbuild.py


In rffi_ there are various declared types for C-structures, like CCHARP
(char*), SIZE_T (size_t) and others. refer to file for details. 
Instances of non-primitive types must be alloced by hand, with call 
to lltype.malloc, and freed by lltype.free both with keyword argument 
flavor='raw'. There are several helpers like string -> char*
converter, refer to the source for details.

.. _rffi: https://bitbucket.org/pypy/pypy/src/tip/pypy/rpython/lltypesystem/rffi.py

Registering function as external

Once we provided low-level implementation of an external function,
would be nice to wrap call to some library function (like os.open)
with such a call. For this, there is a `register_external` routine,
located in `extfunc.py`_, which provides nice API for declaring such a
functions, passing llimpl as an argument and eventually llfakeimpl
as a fake low-level implementation for tests performed by an llinterp.

.. _`extfunc.py`: https://bitbucket.org/pypy/pypy/src/tip/pypy/rpython/extfunc.py

OO backends

XXX to be written