[boost] Re: Boost.Threads: Do we need all those mutexes?

From: David Abrahams (dave_at_[hidden])
Date: 2004-07-08 13:46:13

Howard Hinnant <hinnant_at_[hidden]> writes:

> On Jul 8, 2004, at 11:10 AM, David Abrahams wrote:
>
>> Are there really any repercussions from making a noncopyable type into
>> a moveable type, other than that you might want to find ways to take
>> advantage of the new moveability?
>
> If I had an rvalue reference available today, I would design the
> interface of the read and write locks differently.  For example,
> instead of:
>
>      void f(rw_mutex& m)
>      {
>          rw_mutex::upgradable_read_lock r(m);
>          if (...)
>          {
>              rw_mutex::write_lock w(r);
>              //...
>              w.transfer_to(r);
>          }
>          //Point A
>      }
>
> I would propose:
>
>      void f(rw_mutex& m)
>      {
>          rw_mutex::upgradable_read_lock r(m);
>          if (...)
>          {
>              rw_mutex::write_lock w(move(r));
>              //...
>              r = move(w);
>          }
>          //Point A
>      }
>
> The original code would not compile:  write_lock would not accept an
> lvalue upgradable_read_lock and transfer_to would not exist.

I believe you can have the latter syntax with or without moveability.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com