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From: "Randy Brukardt" <randy@rrsoftware.com>
Subject: Re: Proposal: Auto-allocation of Indefinite Objects
Date: Wed, 19 Aug 2020 19:13:15 -0500	[thread overview]
Message-ID: <rhkf6s$7ph$1@franka.jacob-sparre.dk> (raw)
In-Reply-To: rgr27b$1o1n$2@gioia.aioe.org

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:rgr27b$1o1n$2@gioia.aioe.org...
> On 10/08/2020 02:31, Randy Brukardt wrote:
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
>> news:rfs7k4$c83$1@gioia.aioe.org...
>>> On 29/07/2020 17:33, Brian Drummond wrote:
>>>> On Tue, 28 Jul 2020 16:59:09 +0200, Dmitry A. Kazakov wrote:
>>>
>>>>>>       A constant String := "done";
>>>>>>       Q : indefinite String;
>>>>>>     ...
>>>>>>       loop
>>>>>>          Q := Get_Line;
>>>>>>          exit when Q = A;
>>>>>>       end loop;
>>>>>
>>>>> I am not comfortable with the semantics of this and with possible
>>>>> implications too. I would keep it simple.
>>>>
>>>> Interesting. Can you pin down some of that discomfort? It looks simple 
>>>> to
>>>> me :
>>>>
>>>> "indefinite" indicates the size can vary (and the compiler knows 
>>>> whether
>>>> it used the heap or stack), and in the absence of "aliased" we know 
>>>> there
>>>> are no copies of the pointer (if heap).
>>>
>>> I don't like compiler relocating objects. If the pool is a stack (or 
>>> heap
>>> organized as a stack) it might be unable to do this.
>>
>> This is not that hard to deal with. Janus/Ada handles 
>> discriminant-dependent
>> components of mutable objects this way: they are allocated on the stack, 
>> but
>> if they have to be reallocated they move to the heap.
>
> What you do if such an object is allocated via pool-specific access type?

The whole object goes in that pool. The entire mechanism in Janus/Ada is 
built around pools - the stack is represented by a pool object as well as 
various other pools to support the mechanism.

>> I note that the original idea already exists for discriminant-dependent
>> components -- that's a bit more painful to use but hardly difficult. The
>> main issue is that most compilers fail to support these components 
>> properly,
>> using some sort of max-size implementation unconditionally rather than
>> switching to a pool-based implementation when the max size is too large.
>> I've never understood why Ada compilers were allowed to make such a
>> limitation (it becomes a major limitation when working on non-embedded
>> programs), while similar limitations on case statements and aggregates 
>> are
>> not allowed.
>
> I think a non-embedded target could use a task-local pool for the purpose.

At the cost of using explicit allocators and effectively leaking memory 
(most tasks are fairly long-lived, much longer than the majority of 
objects).

                        Randy.


  reply	other threads:[~2020-08-20  0:13 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-03 22:48 Proposal: Auto-allocation of Indefinite Objects Stephen Davies
2020-04-03 23:45 ` Stephen Leake
2020-04-04 10:54   ` Jeffrey R. Carter
2020-04-04 20:55     ` Stephen Davies
2020-04-04  8:31 ` Dmitry A. Kazakov
2020-07-27  7:47 ` Yannick Moy
2020-07-27  9:21   ` J-P. Rosen
2020-07-27  9:49     ` Dmitry A. Kazakov
2020-07-27 17:48   ` Brian Drummond
2020-07-27 20:02     ` Dmitry A. Kazakov
2020-07-28 14:28       ` Brian Drummond
2020-07-28 14:59         ` Dmitry A. Kazakov
2020-07-29 15:33           ` Brian Drummond
2020-07-29 16:20             ` Dmitry A. Kazakov
2020-07-30 13:37               ` Stephen Davies
2020-07-30 14:23                 ` Dmitry A. Kazakov
2020-07-30 17:04               ` Brian Drummond
2020-07-30 18:28                 ` Dmitry A. Kazakov
2020-08-10  0:39                   ` Randy Brukardt
2020-08-10  8:57                     ` Dmitry A. Kazakov
2020-08-20  0:10                       ` Randy Brukardt
2020-08-20 17:49                         ` Dmitry A. Kazakov
2020-08-20 20:19                           ` Dennis Lee Bieber
2020-08-20 23:33                             ` Randy Brukardt
2020-08-21  6:45                               ` Dmitry A. Kazakov
2020-08-23  4:52                                 ` Randy Brukardt
2020-08-23 12:28                                   ` Dmitry A. Kazakov
2020-08-20 23:30                           ` Randy Brukardt
2020-08-21  6:46                             ` Dmitry A. Kazakov
2020-08-23  4:48                               ` Randy Brukardt
2020-08-23 12:29                                 ` Dmitry A. Kazakov
2020-08-10  0:31               ` Randy Brukardt
2020-08-10  8:58                 ` Dmitry A. Kazakov
2020-08-20  0:13                   ` Randy Brukardt [this message]
2020-08-20 17:49                     ` Dmitry A. Kazakov
2020-08-20 23:25                       ` Randy Brukardt
2020-08-21  7:08                         ` Dmitry A. Kazakov
2020-08-23  5:03                           ` Randy Brukardt
2020-08-23 12:28                             ` Dmitry A. Kazakov
2020-07-27 20:31     ` Jeffrey R. Carter
2020-07-31  9:25 ` Stephen Davies
2020-07-31 10:20   ` Dmitry A. Kazakov
2020-08-01 11:22     ` Stephen Davies
2020-08-01 12:58       ` Dmitry A. Kazakov
2020-08-01 20:35         ` Stephen Davies
2020-08-01 20:56           ` Dmitry A. Kazakov
2020-09-03  4:30 ` linda white
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