From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: is there a version of unix written in Ada
Date: Fri, 2 Oct 2020 08:55:56 +0200 [thread overview]
Message-ID: <rl6its$10h7$1@gioia.aioe.org> (raw)
In-Reply-To: rl5kof$aa8$2@franka.jacob-sparre.dk
On 02/10/2020 00:21, Randy Brukardt wrote:
> [Sorry about breaking the thread, my news server can't handle the depth of
> replies on this thread.]
>
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:rl543q$1om5$1@gioia.aioe.org...
>> On 01/10/2020 19:01, Niklas Holsti wrote:
>>> On 2020-10-01 19:06, Dmitry A. Kazakov wrote:
>>>> On 01/10/2020 17:38, Niklas Holsti wrote:
>>>>
>>>>> If the protected procedures belong to different protected objects, yes
>>>>> it is legal. But not if they belong to the same object, as J-P noted.
>>>>
>>>> But then you have a problem when two independently running protected
>>>> procedures of *different* objects call a procedure of a third object.
>>>> You must serialize these calls, and that is effectively blocking.
>>>
>>>
>>> I don't know what you mean by "effectively", here, but yes, one of the
>>> tasks must wait for the other task to complete the protected operation on
>>> the third object. So what?
>>
>> It looks quite complicated to implement, e.g. checking barriers and doing
>> locking when you are already done that.
>>
>> Now let's continue the example. What happens when the calling paths are:
>>
>> O1.P1 --> O3.P3 --> O2.Q
>>
>> O2.P2 --> O3.P3 --> O2.Q
>
> This latter path is always going to deadlock, since the second call to O2 is
> necessarily an external call (you're inside of O3, not O2). An external call
> has to get the lock for the protected object, and since the lock is already
> in use, that will never proceed.
Is that implementation or requirement? The lock can be task-re-entrant.
> [If O3 was nested in O2, then the second call to O2 could be internal. But
> in that case, the first path would be impossible as O1 could not see O3 to
> call it.]
>
> Remember that the decision as to whether a call is internal or external is
> purely syntactic: if a protected object is given explicitly in the call, one
> needs to trigger the mutual exclusion mechanisms again. The only time one
> doesn't need to do that is when the call does not include the object (that
> is, directly from the body of an operation).
Even when the object in the call is statically known to be same?
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2020-10-02 6:55 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 22:21 is there a version of unix written in Ada Randy Brukardt
2020-10-02 6:55 ` Dmitry A. Kazakov [this message]
2020-10-03 3:09 ` Randy Brukardt
2020-10-03 6:42 ` Dmitry A. Kazakov
2020-10-03 7:44 ` Niklas Holsti
2020-10-03 8:16 ` Dmitry A. Kazakov
2020-10-03 10:44 ` Niklas Holsti
[not found] <e3c51e65-b71e-4623-bd58-c94cdbcc3ba6o@googlegroups.com>
2020-07-25 7:37 ` mockturtle
2020-07-26 19:45 ` Stéphane Rivière
2020-07-26 22:15 ` Jeffrey R. Carter
2020-07-27 7:40 ` Stéphane Rivière
2020-07-28 13:08 ` DrPi
2020-07-28 16:48 ` Simon Wright
2020-07-28 17:00 ` Fabien Chouteau
2020-07-29 9:21 ` DrPi
2020-07-29 9:28 ` Fabien Chouteau
2020-07-29 15:02 ` DrPi
2020-07-29 15:11 ` Fabien Chouteau
2020-07-29 20:41 ` DrPi
2020-07-29 9:20 ` DrPi
2020-07-29 16:53 ` Simon Wright
2020-07-29 20:42 ` DrPi
2020-07-25 8:47 ` Niklas Holsti
2020-07-25 9:36 ` Stéphane Rivière
2020-07-25 10:41 ` Luke A. Guest
2020-07-25 14:43 ` Jesper Quorning
2020-07-25 19:20 ` Andreas ZEURCHER
2020-07-27 7:40 ` Stéphane Rivière
2020-07-27 15:00 ` nobody in particular
2020-07-27 14:58 ` nobody in particular
2020-07-27 20:28 ` Shark8
2020-07-30 0:57 ` gdotone
2020-07-31 14:01 ` Shark8
2020-09-23 17:39 ` Olivier Henley
2020-09-25 15:06 ` DrPi
2020-09-25 17:31 ` Andreas ZEURCHER
2020-09-26 8:50 ` DrPi
2020-09-27 18:55 ` Luke A. Guest
2020-09-27 19:07 ` Luke A. Guest
2020-09-27 18:53 ` Luke A. Guest
2020-09-27 14:25 ` Shark8
2020-09-27 15:01 ` Dmitry A. Kazakov
2020-09-27 20:59 ` DrPi
2020-09-28 7:41 ` Dmitry A. Kazakov
2020-09-28 13:48 ` Olivier Henley
2020-09-28 14:48 ` Dmitry A. Kazakov
2020-09-28 16:28 ` Olivier Henley
2020-09-28 20:30 ` Dmitry A. Kazakov
2020-09-28 21:06 ` Shark8
2020-09-28 17:47 ` Paul Rubin
2020-09-28 20:27 ` Dmitry A. Kazakov
2020-09-29 23:54 ` Paul Rubin
2020-09-30 8:18 ` Dmitry A. Kazakov
2020-09-30 17:27 ` Paul Rubin
2020-09-30 19:42 ` Dmitry A. Kazakov
2020-09-30 20:33 ` Paul Rubin
2020-09-30 21:03 ` Dmitry A. Kazakov
2020-09-30 22:42 ` Randy Brukardt
2020-10-01 9:28 ` Dmitry A. Kazakov
2020-10-01 9:59 ` J-P. Rosen
2020-10-01 10:21 ` Dmitry A. Kazakov
2020-10-01 11:38 ` Niklas Holsti
2020-10-01 11:52 ` Niklas Holsti
2020-10-01 12:51 ` Dmitry A. Kazakov
2020-10-01 14:18 ` J-P. Rosen
2020-10-01 15:44 ` Dmitry A. Kazakov
2020-10-01 22:10 ` Randy Brukardt
2020-10-02 5:36 ` J-P. Rosen
2020-10-02 6:56 ` Dmitry A. Kazakov
2020-10-02 7:42 ` J-P. Rosen
2020-10-03 3:14 ` Randy Brukardt
2020-10-01 15:38 ` Niklas Holsti
2020-10-01 16:06 ` Dmitry A. Kazakov
2020-10-01 17:01 ` Niklas Holsti
2020-10-01 17:37 ` Dmitry A. Kazakov
2020-10-01 22:13 ` Randy Brukardt
2020-10-01 11:48 ` J-P. Rosen
2020-10-01 12:54 ` Dmitry A. Kazakov
2020-10-01 7:57 ` Paul Rubin
2020-10-01 9:26 ` Dmitry A. Kazakov
2020-10-01 9:46 ` Paul Rubin
2020-10-01 10:35 ` Dmitry A. Kazakov
2020-10-01 19:02 ` DrPi
2020-10-01 23:12 ` Paul Rubin
2020-10-01 21:54 ` Randy Brukardt
2020-10-01 23:14 ` Paul Rubin
2020-10-01 21:36 ` Brian Drummond
2020-10-02 6:56 ` Dmitry A. Kazakov
2020-10-02 18:34 ` Brian Drummond
2020-10-02 21:24 ` Paul Rubin
2020-10-06 23:54 ` Brian Drummond
2020-10-03 6:54 ` Dmitry A. Kazakov
2020-10-05 14:03 ` Shark8
2020-10-07 11:56 ` Olivier Henley
2020-10-09 12:35 ` Olivier Henley
2020-10-09 14:41 ` Brian Drummond
2020-09-28 18:40 ` Vincent Marciante
2020-09-28 20:28 ` Dmitry A. Kazakov
2020-09-28 17:04 ` DrPi
2020-09-28 17:30 ` Olivier Henley
2020-09-28 18:05 ` Olivier Henley
2020-09-28 19:36 ` Shark8
2020-09-03 10:32 ` c+
2020-09-12 4:30 ` sumde121
2020-09-19 14:09 ` erchetan33
replies disabled
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox