Re: garbage collection

["Robert I. Eachus" <eachus@mitre.org>]

Ronald Ayoub wrote:
 
> I need this to be clarified for me. If an implementation doesn't provide
> garbage collection then that storage is forever lost, is that correct? Or
> does this mean that it may not be garbage collected but when a call to new
> is executed it is at that time scene as available. Please clarify. This seems
> like a real bad idea not to have some form of garbage collection inforced.

   The correct answer is c) All Ada compilers provide some forms of
storage management, and most Ada programs lose no storage.  But very few
Ada implementations support compacting garbage collectors.

   I could go into all the gory details, but that about sums it up.  The
validation tests do include several tests to insure that storage is not
lost in many common situations, but there is no requirement that storage
be freed the moment their are no more references.  Many Ada compilers
instead free the storage when the access type goes out of scope for some
or all types.

   Why?  Three reasons.  Freeing the storage when the type goes out of
scope allows for predictable storage reclamation which is very useful in
real-time code.  Second, the user can easily manage storage for any type
the way he wants to.  Insisting on "full" garbage collection would limit
the user's choices.

   And finally, Ada allows return values from functions which are
unbounded, and for which the storage is "automagically" managed.  If you
define a function which returns a string in Ada, there is no need for
explicit alloc and free calls or the equivalent.  So in ninety percent
or more of the cases where you need garbage collection in other
languages, you don't even need explicit allocations in Ada.

-- 

                                        Robert I. Eachus

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