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

From: John Maddock (john_at_[hidden])
Date: 2008-04-04 12:01:50

Peter Dimov wrote:
> 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.

:-(

So the question becomes, how do you want these macros to behave?

John.

> 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.
> 
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