Comments on: Gem #77: Where did my memory go? (Part 1)

By: Anh Vo

Anh Vo — Fri, 22 Jan 2010 17:18:56 +0000

It just occurred to me that it could be a memory leak if exception is not raised when accessing (Ptr2.all) Ptr2 when normal memory (default pool) used.

By: Anh Vo

Anh Vo — Thu, 14 Jan 2010 17:40:10 +0000

I agree that it is a good thing to raise GNAT.Debug_Pools.Accessing_Deallocated_Storage exception. In fact, if GNAT.Debug_Pools.Debug_Pool is not used (using default pool), the problem is not detected, and exception is not raised at all.

By: Emmanuel Briot

Emmanuel Briot — Thu, 14 Jan 2010 17:01:35 +0000

As pointed out by Duncan, Ptr has been reset to null, so you get a Constraint_Error. Ptr2, however, still has a non null value, and therefore you get another exception. The good thing is that with a different exception it is clearer where the probleme is

By: Anh Vo

Anh Vo — Thu, 14 Jan 2010 16:54:08 +0000

Of course, there is missing use My_Package clause in the Main subprogram.

It is rather interesting to find out that (Prt2.all := 2;)statement raising GNAT.Debug_Pools.Accessing_Deallocated_Storage exception. However, (Prt.all := 1;) statement raises Constraint_Error.

Why do they trigger different exception?

By: Emmanuel Briot

Emmanuel Briot — Mon, 11 Jan 2010 13:42:36 +0000

Yes, this is true. In fact, the example might useful be changed into

Ptr2 : Integer_Access;
Ptr := new Integer;
Ptr2 := Ptr;
Unchecked_Free (Ptr);
Ptr2.all := 2; — raises exception

By: Duncan Sands

Duncan Sands — Mon, 11 Jan 2010 13:07:59 +0000

I’m not sure that the example says anything about Debug_Pools:
the call to Unchecked_Deallocation will set Ptr to null, so
you would get an exception here whether you used Debug_Pools
or not.