[pypy-commit] pypy default: cppyy doc: introduction of the fast path

[wlav]

Author: Wim Lavrijsen <WLavrijsen at lbl.gov>
Branch: 
Changeset: r54600:e6931441abcb
Date: 2012-04-20 15:28 -0700
http://bitbucket.org/pypy/pypy/changeset/e6931441abcb/

Log:	cppyy doc: introduction of the fast path

diff --git a/pypy/doc/cppyy.rst b/pypy/doc/cppyy.rst
--- a/pypy/doc/cppyy.rst
+++ b/pypy/doc/cppyy.rst
@@ -37,7 +37,7 @@
 easily provided by the packager of your system.
 If you read up on gccxml, you'll probably notice that it is no longer being
 developed and hence will not provide C++11 support.
-That's why the medium plan is to move to `cling`_.
+That's why the medium term plan is to move to `cling`_.
 
 .. _`Download`: http://root.cern.ch/drupal/content/downloading-root
 .. _`source`: http://root.cern.ch/drupal/content/installing-root-source
@@ -241,6 +241,35 @@
 You can always find more detailed examples and see the full of supported
 features by looking at the tests in pypy/module/cppyy/test.
 
+
+The fast lane
+=============
+
+The following is an experimental feature of cppyy, and that makes it doubly
+experimental, so caveat emptor.
+With a slight modification of Reflex, it can provide function pointers for
+C++ methods, and hence allow PyPy to call those pointers directly, rather than
+calling C++ through a Reflex stub.
+This results in a rather significant speed-up.
+Mind you, the normal stub path is not exactly slow, so for now only use this
+out of curiosity or if you really need it.
+
+To install this patch of Reflex, locate the file genreflex-methptrgetter.patch
+in pypy/module/cppyy and apply it to the genreflex python scripts found in
+``$ROOTSYS/lib``::
+
+    $ cd $ROOTSYS/lib
+    $ patch -p2 < genreflex-methptrgetter.patch
+
+With this patch, ``genreflex`` will have grown the ``--with-methptrgetter``
+option.
+Use this option when running ``genreflex``, and add the
+``-Wno-pmf-conversions`` option to ``g++`` when compiling.
+The rest works the same way: the fast path will be used transparently (which
+also means that you can't actually find out whether it is in use, other than
+by running a micro-benchmark).
+
+
 CPython
 =======