HPX fails on startup (setting thread affinity mask)

[eschnett]

I use HPX on OS X, configured with hwloc. The hwloc library is e.g. useful for determining the number of cores and cache sizes. However, on OS X it cannot set thread bindings, as this is not allowed by the OS.

On startup, HPX fails with the error message:

terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<hpx::exception> >'
  what():  failed to set thread fe affinity mask: HPX(kernel_error)

(1) This error message is a bit cryptic; it is not clear that "fe" corresponds to a thread mask.
(2) This error is expected; HPX should output a warning instead, and then continue, instead of aborting.