The System.Pool_Global package offers the Unbounded_No_Reclaim_Pool
storage pool. Allocations use the standard system call malloc while
deallocations use the standard system call free. No reclamation is
performed when the pool goes out of scope. For performance reasons, the
standard default Ada allocators/deallocators do not use any explicit storage
pools but if they did, they could use this storage pool without any change in
behavior. That is why this storage pool is used when the user
manages to make the default implicit allocator explicit as in this example:
type T1 is access Something;
-- no Storage pool is defined for T2
type T2 is access Something_Else;
for T2'Storage_Pool use T1'Storage_Pool;
-- the above is equivalent to
for T2'Storage_Pool use System.Pool_Global.Global_Pool_Object;
The System.Pool_Local package offers the Unbounded_Reclaim_Pool storage
pool. The allocation strategy is similar to Pool_Local's
except that the all
storage allocated with this pool is reclaimed when the pool object goes out of
scope. This pool provides a explicit mechanism similar to the implicit one
provided by several Ada 83 compilers for allocations performed through a local
access type and whose purpose was to reclaim memory when exiting the
scope of a given local access. As an example, the following program does not
leak memory even though it does not perform explicit deallocation:
with System.Pool_Local;
procedure Pooloc1 is
procedure Internal is
type A is access Integer;
X : System.Pool_Local.Unbounded_Reclaim_Pool;
for A'Storage_Pool use X;
v : A;
begin
for I in 1 .. 50 loop
v := new Integer;
end loop;
end Internal;
begin
for I in 1 .. 100 loop
Internal;
end loop;
end Pooloc1;
The System.Pool_Size package implements the Stack_Bounded_Pool used when
Storage_Size is specified for an access type.
The whole storage for the pool is
allocated at once, usually on the stack at the point where the access type is
elaborated. It is automatically reclaimed when exiting the scope where the
access type is defined. This package is not intended to be used directly by the
user and it is implicitly used for each such declaration:
type T1 is access Something;
for T1'Storage_Size use 10_000;