Re: is there a version of unix written in Ada

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 2020-10-01 15:51, Dmitry A. Kazakov wrote:
> On 01/10/2020 13:38, Niklas Holsti wrote:
>> On 2020-10-01 13:21, Dmitry A. Kazakov wrote:
>>> On 01/10/2020 11:59, J-P. Rosen wrote:
>>>> Le 01/10/2020 à 11:28, Dmitry A. Kazakov a écrit :
>>>>> BTW, I still do not know to design an Ada-conform tracing/logging
>>>>> facility such that you could trace/log from anywhere, protected action
>>>>> included, and without knowing statically which protected object is
>>>>> involved.
>>>>>
>>>> Did you have a look at package Debug?
>>>> (https://www.adalog.fr/en/components#Debug)
>>>
>>> Thanks
>>>
>>>> It features, among others, a trace routine which is guaranteed to 
>>>> not be
>>>> potentially blocking.
>>>
>>> It calls a protected operation on a different protected object, yes, 
>>> this is non-blocking, and I considered same, but is this legal?
>>
>> Yes.
>>
>> If the program is using ceiling-priority-based protection, the 
>> priority of the calling object must be less or equal to the priority 
>> of the called object.
> 
> My mental picture was protected procedure calls executed concurrently on 
> different cores of a multi-core processor. Would that sort of 
> implementation be legal?


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.

Note that the ordinary form of the ceiling-priority-locking method does 
not work for multi-cores, because a task executing at the ceiling 
priority of a protected object does not prevent the parallel execution 
of other tasks (on other cores) at the same or lower priority.


>> 2. A task that empties the [FIFO] queue into a log file. The task calls 
>> an entry of the [FIFO] protected object to get a log entry from the 
>> queue, but executes the file-writing operations in task context, not 
>> in a protected operation.
> 
> A simpler approach is to flush the queue by the first call to an 
> unprotected variant of Trace. I believe Debug.adb does just this.


That is ok for programs that run for a short while, then terminate. Most 
of my programs are non-terminating embedded programs so the log has to 
be emitted from RAM to some larger storage continuously as the program 
is running.