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Re: Custom Storage Pool questions

Newsgroups comp.lang.ada
Date 2021-09-16 00:12 -0700
References <e3c5c553-4a7f-408a-aaa7-60ec0b70202dn@googlegroups.com> <ly5yv1bxgy.fsf@pushface.org> <shtg99$tgd$1@gioia.aioe.org> <lywnnha7y1.fsf@pushface.org>
Message-ID <1d2551f4-8189-44ec-a54d-4a56a672bedcn@googlegroups.com> (permalink)
Subject Re: Custom Storage Pool questions
From Emmanuel Briot <briot.emmanuel@gmail.com>

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I am the original implementor of GNATCOLL.Storage_Pools.Headers, and I have been silent in this discussion because I must admit I forgot a lot of the details... To be sure, we did not add new attributes just for the sake of GNATCOLL, those existed previously so likely had already found other uses.

As has been mentioned several time in the discussion, the compiler is already passing the full size it needs to Allocate, and the storage pool only needs to allocate that exact amount in general. This applies for the usual kinds of storage pools, which would for instance preallocate a pool for objects of fixed sizes, or add stronger alignment requirements.

In the case of the GNATCOLL headers pool, we need to allocate more because the user wants to store extra data. For that data, we are left on our own to find the number of bytes we need, which is part of the computation we do: we of course need the number of bytes for the header's object_size, but also perhaps some extra bytes that are not returned by that object_size in particular for controlled types and arrays.
Note again that those additional bytes are for the header type, not for the type the user is allocating (for which, again, the compiler already passes the number of bytes it needs).

The next difficulty is then to convert from the object's 'Address back to your extra header data. This is when you need to know the size of the prefix added by the compiler (array bounds, tag,...) to skip them and then take into account the alignment, and finally the size of your header.
Dmitry's suggested exercice (storing the timestamp of the allocation) seems like a useful one indeed. It would be nice indeed if GNATCOLL's code was too complicated, but I am afraid this isn't the case. We had used those pools to implement reference counting for various complex types, and ended up with that complexity.

AdaCore (Olivier Hainque) has made a change to the implementation since the blog was published (https://github.com/AdaCore/gnatcoll-core/commits/master/src/gnatcoll-storage_pools-headers.adb), so I got some details wrong in the initial implementation apparently.

Emmanuel

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Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-12 17:53 -0700
  Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-13 00:29 -0500
    Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-13 18:04 -0700
      Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:06 -0500
    Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-09-18 12:32 +0100
    Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-19 17:31 -0700
      Re: Custom Storage Pool questions Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-09-20 09:34 +0300
        Re: Custom Storage Pool questions Emmanuel Briot <briot.emmanuel@gmail.com> - 2021-09-19 23:48 -0700
          Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-20 09:35 +0200
          Re: Custom Storage Pool questions Shark8 <onewingedshark@gmail.com> - 2021-09-20 09:59 -0700
          Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:50 -0500
            Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-21 16:08 -0700
              Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-27 23:42 -0500
                Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-10-02 16:19 -0700
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-03 10:52 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-10-13 20:26 -0500
  Re: Custom Storage Pool questions "J-P. Rosen" <rosen@adalog.fr> - 2021-09-13 13:12 +0200
    Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-13 17:48 -0700
      Re: Custom Storage Pool questions "J-P. Rosen" <rosen@adalog.fr> - 2021-09-14 08:08 +0200
        Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-14 17:39 -0700
          Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-09-15 08:01 +0100
            Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-16 16:32 -0700
              Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 18:51 -0500
                Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-21 15:40 -0700
      Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-14 08:23 +0200
        Re: Custom Storage Pool questions "J-P. Rosen" <rosen@adalog.fr> - 2021-09-14 08:42 +0200
          Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-14 09:00 +0200
          Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 18:58 -0500
        Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-14 17:21 -0700
          Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-15 08:54 +0200
        Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 18:48 -0500
      Re: Custom Storage Pool questions Egil H H <ehh.public@gmail.com> - 2021-09-14 03:54 -0700
        Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-14 17:11 -0700
  Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-09-15 17:43 +0100
    Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-09-15 18:03 +0100
    Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-15 21:07 +0200
      Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-09-15 21:40 +0100
        Re: Custom Storage Pool questions Emmanuel Briot <briot.emmanuel@gmail.com> - 2021-09-16 00:12 -0700
          Re: Custom Storage Pool questions Jere <jhb.chat@gmail.com> - 2021-09-16 16:21 -0700
            Re: Custom Storage Pool questions Emmanuel Briot <briot.emmanuel@gmail.com> - 2021-09-17 00:08 -0700
            Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-09-17 08:18 +0100
            Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-17 15:56 +0200
              Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-09-17 20:46 +0100
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-17 22:39 +0200
                Re: Custom Storage Pool questions Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-09-18 00:17 +0300
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-18 09:49 +0200
                Re: Custom Storage Pool questions Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-09-18 12:03 +0300
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-18 12:22 +0200
                Re: Custom Storage Pool questions Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-09-18 18:59 +0300
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-18 18:19 +0200
                Re: Custom Storage Pool questions Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-09-19 13:36 +0300
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-19 13:41 +0200
                Re: Custom Storage Pool questions Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-09-20 10:05 +0300
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-20 09:35 +0200
                Re: Custom Storage Pool questions Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-09-20 11:08 +0300
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-20 10:28 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:45 -0500
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:40 -0500
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:30 -0500
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:37 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-21 08:28 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-27 23:38 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-28 09:00 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:26 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-21 08:51 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-27 23:31 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-28 08:56 +0200
                Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-09-28 08:52 +0100
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-28 10:07 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-28 17:04 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-29 09:57 +0200
                Re: Custom Storage Pool questions Shark8 <onewingedshark@gmail.com> - 2021-09-29 07:41 -0700
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-29 17:16 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-29 19:16 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-30 10:08 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-30 19:04 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-01 10:25 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-10-02 04:06 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-02 12:18 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-10-02 23:33 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-03 10:40 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-10-13 20:21 -0500
                Re: Custom Storage Pool questions "philip...@gmail.com" <philip.munts@gmail.com> - 2021-10-13 20:12 -0700
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-14 09:31 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-10-14 19:36 -0500
                Re: Custom Storage Pool questions Stephen Leake <stephen_leake@stephe-leake.org> - 2021-10-15 01:08 -0700
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-15 10:18 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-10-15 17:22 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-15 10:15 +0200
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-10-15 17:44 -0500
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-16 11:00 +0200
                Re: Custom Storage Pool questions Simon Wright <simon@pushface.org> - 2021-10-16 15:32 +0100
                Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-10-16 17:06 +0200
                Re: Custom Storage Pool questions Shark8 <onewingedshark@gmail.com> - 2021-10-18 07:23 -0700
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:19 -0500
                Re: Custom Storage Pool questions "Randy Brukardt" <randy@rrsoftware.com> - 2021-09-20 19:18 -0500
        Re: Custom Storage Pool questions "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2021-09-16 10:41 +0200

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