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Subject: Re: [Boost-build] bjam 4.0.. in C++
From: Belcourt, Kenneth (kbelco_at_[hidden])
Date: 2010-05-24 16:56:23

Hi Spencer,

On May 24, 2010, at 9:15 AM, Spencer E. Olson wrote:

> I've heard that one of the Sandia projects that was attempting to use
> Boost.Build did suffer from speed issues with bjam.

Ah yes, the grapevine...

Speed issues... a long subject. When we replaced our in-house
developed tools with Boost.Build, we found the build speed /
throughput to be the same as the limited capability in-house tools we
were replacing. Once we had a functioning minimal (Boost) build
system we went on to move all of our source code, including third
party libraries we depend on, into Boost.Build, and here we noticed a
considerable slowdown. Because we'd never had the ability to use a
single build system to build our entire (developed and dependent) code
base from source, the slowdown didn't concern me too much and it
wasn't an impediment for our external customers. Some of our internal
developers, on the other hand, were quite bothered by it so they went
on to wrap the Boost build system in a Make layer (called Bake). Bake
would run bjam, capture the build commands, write them to a makefile
and then Bake would just invoke make on this makefile.

Our key performance problem with Boost.Build was recomputing the
dependencies from scratch each time the user ran bjam so the Bake
layer amortized this cost (run bake 50 times, then rerun bjam to bring
dependencies up to date) at the expense of firmly pushing the
dependency tracking obligation onto the users. Because most
developers work inside a single library where the include and library
dependencies don't change that often, this tradeoff was considered
acceptable. Our developers also have significant problems grokking
the Jamfile syntax but a handful of them have learned how to modify
the Jamfiles and interpret the error messages. Jamfile changes are
rather less common now that the system has been in production and
stable for a few years. Given the complexity of what we do,
Boost.Build delivered a product that, with significant customization,
has virtually eliminated the build system as an impediment to either
our external customer or internal developer productivity. That's a
pretty significant accomplishment IMO.

-- Noel

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