Re: [boost] [config] BOOST_DISABLE_THREADS defined by Boost.Config

From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-04-04 08:53:01

John Maddock wrote:

> Doug, what effect would none of BOOST_HAS_WINTHREADS,
> BOOST_HAS_PTHREADS and BOOST_HAS_THREADS being defined have on
> shared_ptr?

Well.

BOOST_HAS_THREADS is an overloaded macro. It can mean one of two things:

1. Whether the compiler/runtime is in multithreaded mode. In this case, the 
absence of BOOST_HAS_THREADS would indicate that the compiler/runtime only 
supports a single thread, and hence, a library may use that to safely 
disable synchronization.

2. Whether a threading API is available. In this case BOOST_HAS_WINTHREADS 
and BOOST_HAS_PTHREADS provide additional information about which API is 
available.

The problem is that BOOST_HAS_THREADS isn't very useful in practice, no 
matter what meaning is chosen. Its absence cannot be used to assume a single 
thread (because it gets turned off when there's no threading API), and it 
cannot be used to assume lack of threading API (because of 
BOOST_DISABLE_WIN32.)

So shared_ptr ignores it as much as it can.

To get back to your question, BOOST_HAS_WINTHREADS is not used by 
shared_ptr, so it doesn't matter whether it's defined or not.