[Boost-build] Help optimizing a slow BJAM build

From: Igor Nazarenko (igor.n.nazarenko_at_[hidden])
Date: 2008-04-03 14:34:25

I have a relatively small project, currently consisting of ~200 C++
files and headers. The project makes heavy use of BOOST 1.34, and also
uses Xerces which adds another bunch of headers. The end result is
that BJAM reports ~14,000 targets. Even when the build doesn't
actually compile or link anything, BJAM is taking almost a minute on
our fastest machine:

$ time bjam -j8 variant=debug,release
...patience...
...patience...
...patience...
...found 13910 targets...

real    0m56.029s
user    0m55.802s
sys     0m0.208s

I'm attaching the BJAM profile (obtained by running "bjam -n -d+10
variant=debug,release > profile.txt").

>From looking at that profile, it seems that the major portion of time
is spent in the following chain:
class_at_install-target-class.collect-targets -> sequence.unique -> SORT.
Looking at the source code of SORT in lists.c, it seems to me that the
function (list_sort) is more complicated than it needs to be, and may
be degrading to quadratic behavior on somewhat-pre-sorted lists. I
could try to change it to allocate an array of string pointers and
sort it by standard qsort().

However, before I go there, two questions:
- is it possible to tell Boost.Build system that the BOOST and XERCES
headers are static, and there's no need to include them in the list of
dependencies?
- if I re-code list_sort() function in boost-build/jam_src/lists.c,
what's the procedure to get the patch into the "official" source tree?
Is it even possible?

Thanks a lot in advance

Igor Nazarenko