[Boost-build] Effect of usage requirements vs. default values of a feature

Subject: [Boost-build] Effect of usage requirements vs. default values of a feature
From: Gevorg Voskanyan (v_gevorg_at_[hidden])
Date: 2011-04-16 11:13:52

Perhaps I'm touching an old ground, but let's consider the following case:

lib a : a.cpp : <threading>multi : : <threading>multi ;
exe e : e.cpp a ;

bjam -n -a gives the output contained in bjam-n-a.log

Basically there is no -pthread passed when building 'e', even 
though threading-multi is contained within the path to the produced binary.

bjam -a --debug-building gives the output contained 
in bjam-a--debug_building.log

Which shows e's build properties to contain both <threading>single and 
<threading>multi, resulting in undefined reference to `pthread_create' link 
error.

How is it possible for a non-free feature to have more than one value for a 
given target? Is this example supposed to work?

Thanks,
Gevorg