Re: Deallocating an object twice

[anon@att.net]

For most OS, deallocation of memory happens only if the program 
exits and returns it's allocated resources back to the OS. And 
for speed the underlying C library routine "free" does not truly
deallocate or mark the memory as unused. Which means passing a 
null pointer to the underlying C library function "free" will not 
generate an error, so neither does Ada.  This is apart of a bigger 
topic call "Garbage Collection".

Note: In the GNAT design if a storage pool is not present, the 
memory access is done by calling "System.Memory.Free" routine 
which only calls the underlying C library. So, no exception 
will be generated.

To correct this and limit the number of memory leaks, a program 
may employ a storage pool ( like the generic abstract package 
System.Storage_Pool ), and add the exception in the deallocation 
routine. But this feature does have this down sides, like slower 
speed and larger footprint for maintaining a allocation tables.

Note: GNAT does have a number of storage pools designs.

As for the exception it would fall under the Storage_Error scope.
The "Program_Error" exception are for special cases. 


In <lr1142$log$1@speranza.aioe.org>, Victor Porton <porton@narod.ru> writes:
>If I understand correctly, it is an undefined behavior (or is it called 
>unbounded error?) if a pool access is deallocated twice with 
>Unchecked_Deallocation.
>
>I think it should be a Program_Error (if checks are on).
>
>Why was not this done even in Ada2012 (not speaking about older Ada)?
>
>It's bad.
>
>Or is it done and I just miss it?
>
>-- 
>Victor Porton - http://portonvictor.org