Re: [boost] Re: Boost.Threads - thread_desc concept

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2001-06-27 11:01:01

From: <williamkempf_at_[hidden]>
> --- In boost_at_y..., "Greg Colvin" <gcolvin_at_u...> wrote:
> > ... 
> > You can let the OS do the counting:
> > 
> > 
> > class thread_ref {
> >    HANDLE id;
> > public:
> >    thread_ref(const thread_ref& r) {
> >       if (!DuplicateHandle(GetCurrentProcess(),r.id,
> >                            GetCurrentProcess(),&id,
> >                            0,false,DUPLICATE_SAME_ACCESS))
> >          throw something;
> >    }
> >    thread_ref& operator=(const thread_ref& r) {
> >       if (&r != this) {
> >          this->~thread_ref();
> >          new(this) thread_ref(r);
> >       }
> >    }
> >    ~thread_ref() { CloseHandle(id); }
> > 
> >    void join();
> >    ...
> > 
> > };
> 
> Not all platforms can handle this in the same way, though, including 
> pthreads.

Right, and on those platforms you can count explicitly.  For
all I know DuplicateHandle is more expensive than an explicit
count even on Windows, but I suspect not, especially once you
make the counter thread safe.  Although to be thread safe the
assignment probably needs to be:

   thread_ref& operator=(const thread_ref& r) {
      HANDLE new;
      if (!DuplicateHandle(GetCurrentProcess(),r.id,
                           GetCurrentProcess(),&new,
                           0,false,DUPLICATE_SAME_ACCESS))
      CloseHandle(id);
      id = new;
   }