Re: [Boost-users] [MSM] state transitions and exceptions

On 01.04.2012, at 22:13, Christophe Henry wrote:

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on Thu Mar 29 2012, "Christophe Henry" wrote:

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Jurai,

On Thu, Mar 29, 2012 at 7:07 PM, Juraj Ivančić wrote:

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I know how you feel. MSM is an awesome library. Unfortunately compilers tend to disagree :)

I'd say compilers should be blamed for this ;-) (I'm still wondering how it can be that compilers make such a poor use of my 6 cores with hyperthreading when compile a single object file...)

There isn't much inherent parallelism to exploit in C++ compilation of a single translation unit.

-- Dave Abrahams BoostPro Computing http://www.boostpro.com

I'm not an expert in this field, but this surprises me a bit. I understand that there is not much parallelism in parsing a file, but after? Taking msm as example. Most of the compile time comes from template instanciations of the function process_event for every event type. Adding support for a new event adds roughly the same compilation time. Every process_event has little in common with other process_event instances. What prevents the compiler from handling each at the same time?

The locking mechanism for ASTs would probably be very complicated if you want to do template instantiation in parallel. It probably could be done, but going that route isn't very attractive because the cores are much better used compiling 6 files in parallel.

Sebastian

Sure but it's still very annoying because in a well-designed application with little dependency, I work very very often on a single cpp file where my state machine (or other boost-heavy code) is used and have to wait up to 2mn that this file is compiled with 1 thread while my other 11 are bored. Then I wait until linking is done, on 1 thread. This doesn't look like a very good usage of my cores either ;-) I hereby make the promise to switch all my applications to the first standard-conform compiler which compiles this one file on 12 threads thus saving me hours per year :) Christophe