Re: [boost] boost] [thread] Interest in a locking pointer and lockable concept

From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2008-04-03 09:37:12

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On Wednesday 02 April 2008 16:46 pm, klaus triendl wrote:
> Phil Endecott schrieb:
> > i.e. LockableRef contains a reference to the mutex and one element of
> > its "parent" Lockable<>, and presents the same interface as a data-full
> > Lockable<>.
> >
> > But because Lockable and LockableRef aren't actually the same type, I
> > can't write
> >
> > void start_updater(Lockable<int> i);
> >
> > and use it with both.
> >
> > Is this something that you have thought about?
>
> Well, I didn't think about this one. But what do you think of the
> following?
>
>
> <code>
> template<typename T_type, typename T_mutex>
> struct lockable //: ...
> {
>      // ...
>
>      // return a lockable_ref, see below
>      lockable_ref<std::tr1::remove_extent<T_type>, T_mutex>
>      operator [](std::size_t idx)
>      {
>          return lockable_ref<std::tr1::remove_extent<T_type>,
> T_mutex>(access_volatile()[idx], mutex());
>      }
> };

This would only support array-like types.  Are you familiar with the aliasing 
constructor of shared_ptr?  I put something similar in poet::monitor_ptr, but 
it's only in cvs at the moment.  Anyways, it's a more general solution to 
this kind of situation, although it doesn't provide much of a safeguard 
against misuse.  Anyways, your example snippet would look something like 
this:

<code>
void start_updater(poet::monitor_ptr<int> i)
{
//...
}

poet::monitor_ptr<array<int, 100> > values;
poet::monitor_ptr<int> one_value;

//...

for (int i=0; i<100; ++i) {
    start_updater(poet::monitor_ptr<int>(values, &values->at(i)));
}

start_updater(one_value);
</code>

- -- 
Frank
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