13.11.5 Subpool Reclamation
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A subpool may be explicitly deallocated using Unchecked_Deallocate_Subpool.
Static Semantics
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The following language-defined library procedure exists:
with System.Storage_Pools.Subpools;
procedure Ada.Unchecked_Deallocate_Subpool
(Subpool :
in out System.Storage_Pools.Subpools.Subpool_Handle);
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If Subpool is
null, a call on Unchecked_Deallocate_Subpool has
no effect. Otherwise, the subpool is finalized, and Subpool is set to
null.
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Finalization of a subpool has the following effects:
The subpool no longer belongs to any pool;
Any of the objects allocated from the subpool that
still exist are finalized in an arbitrary order;
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All of the objects allocated from the subpool cease to exist;
The following [dispatching]
call is then made:
Deallocate_Subpool(Pool_of_Subpool(Subpool).all, Subpool);
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Finalization of a Root_Storage_Pool_With_Subpools object finalizes all
subpools that belong to that pool that have not yet been finalized.
Discussion: There is no need to call
Unchecked_Deallocation on an object allocated in a subpool. Such objects
are deallocated all at once, when Unchecked_Deallocate_Subpool is called.
If Unchecked_Deallocation is called, the object
is finalized, and then Deallocate is called on the Pool, which typically
will do nothing. If it wants to free memory, it will need some way to
get from the address of the object to the subpool.
There is no Deallocate_From_Subpool. There is
no efficient way for the implementation to determine the subpool for
an arbitrary object, and if the pool implementer can determinate that,
they can use that as part of the implementation of Deallocate.
If Unchecked_Deallocation is not called (the
usual case), the object will be finalized when Unchecked_Deallocate_Subpool
is called.
If that's never called, then the object will
be finalized when the Pool_With_Subpools is finalized (by permission
— it might happen when the collection of the access type is finalized).
Extensions to Ada 2005
Wording Changes from Ada 2012
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Corrigendum: Added missing wording to state that the objects cease
to exist after the completion of finalization. This is formally an inconsistency
(it would be possible to depend on the fact that objects finalized by
Unchecked_Deallocate_Subpool still exist), but that violates every sane
expectation for a procedure called "Deallocate" something.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
