[Boost-users] smart_ptr without memory allocation

From: John Aughey (jha_at_[hidden])
Date: 2003-10-19 18:59:11

I have a class that implements a buffer pool that allocates block of
memory, and the users "free" the memory when it is no longer needed back
to the buffer pool.  Future allocations simply return the front of the
free list.

Simple enough, and the class returns shared_array<T> objects to
automatically free the memory back into the proper buffer pool.

The problem is, this mechanism is used so that during real-time operation
(this is a real-time system), there is absolutely no memory allocations
required.  However, inside shared_array, it uses detail::shared_count and
inside shared_count it performs a new to create a sp_counted_base object.
So for every smart pointer object that supplies a deleter, it must perform
a new.

My proposal would be to include another constructor to both shared_array
(and probably it's corresponding smart pointer brothers) and to
shared_count that looks like:

shared_array(T *p, sp_counted_base *d) : px(p), pn(d) { }

shared_count(sp_counted_base *d) : pi_(d) { }

(I haven't implemented this yet, so the above may not be quite right)

The purpose of this is to supply an sp_counted_base object to the shared_*
object that does the delete functionality.  This eliminates the new in the
case where a sp_counted_base object can be supplied.  In the case of the
managed buffer pool mentioned above, the sp_counted_base object could be
allocated with the corresponding buffer, and then re-used for subsequent
"allocations" from the free list.  This should result in no dynamic
allocations to create a shared_* object with a corresponding deleter.

I hope this makes sense.  It should only require two new constuctors.

John