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* Re: is there a version of unix written in Ada
@ 2020-10-01 22:21 Randy Brukardt
  2020-10-02  6:55 ` Dmitry A. Kazakov
  0 siblings, 1 reply; 105+ messages in thread
From: Randy Brukardt @ 2020-10-01 22:21 UTC (permalink / raw)


[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.

[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).

                                       Randy.



^ permalink raw reply	[flat|nested] 105+ messages in thread

end of thread, other threads:[~2020-10-09 14:41 UTC | newest]

Thread overview: 105+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
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2020-07-25  7:37 ` is there a version of unix written in Ada 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
2020-10-01 22:21 Randy Brukardt
2020-10-02  6:55 ` Dmitry A. Kazakov
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

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