Re: [Boost-build] Recursively dependent libs

From: Rene Rivera (grafikrobot_at_[hidden])
Date: 2006-09-19 00:15:38

Vladimir Prus wrote:
> Rene,
> in 
> 
>    https://zigzag.cs.msu.su:7813/boost.build/ticket/81
> 
> you said V2 does not support recursively dependent libs. I believe you've 
> added the --start-group/--end-group to gcc command line to address that. Is 
> the issue now closed?

No. I added the issue so that possibly one of the other options would be 
implemented. Unless we think that what I did is a real solution.

> Incidentally, we have quite a lot of code to property order libraries on 
> command line for Unix. I'm not sure what to do with that code. It was written 
> because some folks said --start-group causes performance degradation. 

It is slower. But at worse it's only 2 times slower than a regular build 
as using the group options is equivalent to repeating the libraries. I 
think the ideal solution is to only group recursive libs when we detect 
them (the last option I list on the issue). But I don't know how 
complicated would be to implement. I was hoping you could tell me ;-)

> It would be interesting to know if --start-group causes performance 
> degradation even if there are no circular dependencies and libraries on 
> command line are property sorted.

Hm, good question! It's my understanding, but only from the docs, that 
it tries to be optimal in that it only rescans the libraries if there 
are unresolved symbols. So I would think that on the optimal, i.e. no 
interdependency libs it would scan only once.

> If yes, and that performance degradation is serious, we might need to have an 
> option 'allow circular dependencies'
> 
> If no, then --start-group is way to allow circular dependencies without 
> penalizing common case, so we can just close the issue.
> 
> Any options?
> 
> BTW, why do you have circular dependencies between libraries at all?

Truthfully I don't remember why. My vague memory is that it's not my 
code that has it, but some third party code I use. I personally don't 
intentionally have them as I know how painful they are to make work :-)

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