Re: [boost] Interest in an Active Object CRTP "decorator"?

Subject: Re: [boost] Interest in an Active Object CRTP "decorator"?
From: Dean Michael Berris (mikhailberis_at_[hidden])
Date: 2008-11-10 02:24:58

Hi Vicente!

On Sun, Nov 9, 2008 at 1:06 AM, vicente.botet <vicente.botet_at_[hidden]> wrote:
[snip]
>
> Why the usual constructor is not enough -- init is called after active is
> constructed?

Good question. Actually, you're right. I got confused about the order
of construction/destruction.

> IMO
>     static_cast<Derived*>(this)->destroy();
> is very dangerous. You are calling a function for an object that has already
> been destructed, so any access to Derived data is undefined.
>

Again, you're right.

> So ath the end whay do you need CRTP?
> Why do you need the usual constructor is not enough -- init is called after
> active is constructed?
>

It looks like CRTP is no longer needed. :-)

So it will look something like this:

template <class ThreadingPolicy>
struct active : ThreadingPolicy {
  private:
    shared_ptr<io_service> queue;
    shared_ptr<io_service::work> sentinel;
    typename ThreadingPolicy::thread_type lifetime_thread;
  protected:
    active() :
    ThreadingPolicy(),
    queue(new io_service()),
    sentinel(new io_service::work(*queue))
    {
      ThreadingPolicy::init_threading(lifetime_thread, queue);
    }

    ~active() {
      sentinel.reset();
      ThreadingPolicy::destroy_threading(lifetime_thread);
    }

    void post(function<void()> f) {
      queue->post(ThreadingPolicy::wrap(f));
    }
};

Now the active object is no longer constrained to a single thread by
choosing the correct policy.

struct single_thread {
  protected:
    typedef shared_ptr<thread> thread_type;
    void init_threading(thread_type t, shared_ptr<io_service> q) {
      t.reset(new thread(
        bind(&io_service::run, q)
        )
      );
    }
    void destroy_threading(thread_type t) {
      t->join();
    }
    function<void()> wrap(function<void()> f) {
      return f;
    }
};

struct thread_pool {
  // ...
};

Thanks for the insights, any interest in seeing something like this in Boost?

-- 
Dean Michael C. Berris
Software Engineer, Friendster, Inc.