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From: "Alejandro R. Mosteo" <alejandro@mosteo.com>
Newsgroups: comp.lang.ada
Subject: Re: Launching background job from Ada.Real_Time.Timing_Events
Date: Fri, 3 Jun 2016 12:03:53 +0200
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Date: 2016-06-03T12:03:53+02:00
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On 03/06/16 09:26, Dmitry A. Kazakov wrote:
> On 02/06/2016 23:25, Alejandro R. Mosteo wrote:
>
>> I'm sorry but I don't follow your explanation. To make things simpler,
>> let's consider only the 1-to-1 case. How's this protected used without a
>> blocking operation?
>
> If you have FIFO, a lock-free implementation is a buffer with one read
> and one write index (mod buffer length). The read index never advances
> beyond the write index. Reader updates the read index and looks at the
> write index, and conversely the writer. Indices must have pragma Atomic,
> and the buffer not cached. For example:
>
> http://www.dmitry-kazakov.de/ada/components.htm#10.1.1

Thanks, I was unsure if you referred to using a lock-free data type, or 
if it could be trivially done with the standard Ada containers with some 
well-known pattern I was ignorant of.

I'll take a look at your library, I'm very interested in lock-free 
containers.

A friend working on hardware architectures recently told me that a 
widely-used lock-free library (in the c++ world) had been proven with 
SPARK-like methods to be buggy. Alas, I can't remember names/dates.

Thanks,
Alex.

>
> Of course if you want to wait for a FIFO state, e.g. 'not full' or 'not
> empty' you will need an event (a protected object). But you don't need
> to have the FIFO a protected object.
>
> It is an important point not to have containers protected. Operations on
> container might be quite expensive depending on the element types and
> the container structure. As a rule you should not maintain containers on
> the context of a protected action. E.g. if you have to do a binary
> search to get an element, that is not to do in a protected action.
>
>>>> Any ideas? Basically, how to trigger another task (without creating it)
>>>> from within a protected handler?
>
> By changing an entry barrier, of course.
>
> The task to trigger waits for a protected entry to open, it is released
> after leaving the entry.
>