Re: Multitasking and containers

Dmitry A. Kazakov wrote:

Paragraph 3 in Annex A says that it's OK to call any standard subprogram from concurrent tasks as long as the parameters do not overlap. John Barnes ("Progamming in Ada 2005") suggests that in order to (for example) read from the same container, the operations need to be protected "by using the normal techniques such as protected objects".

But reading from the protected object is not mutually exclusive (many readers are allowed) - so where's the gain? What's the difference between concurrent reads of, say, a Vector via protected object vs. direct access?

I think he didn't mean container being a protected object.

No, but you might want to encapsulate a container within a protected object and have some protected procedures and functions forwarding to relevant ones in the container.

[ I don't know if ARM 2005 permits mutable implementations of read
operations on the containers. I suppose it does, so the need to lock upon
read. ]

That would be interesting, but would break apart when encapsulated within a protected object, because there multiple readers would be allowed.

Having a mutex for readers sounds like a concurrency killer and relying on protected wrappers seems to be fragile because of this possible mutability. So - what is The Solution (tm) for multiple tasks reading from the same container?

Let's say you want to have N worker tasks consulting a shared dictionary (map) that was initialized before the tasks started their work. How would you solve this?

--
Maciej Sobczak : http://www.msobczak.com/
Programming : http://www.msobczak.com/prog/
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Relevant Pages

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  • Re: Multitasking and containers
    ... from concurrent tasks as long as the parameters do not overlap. ... protected "by using the normal techniques such as protected objects". ... But reading from the protected object is not mutually exclusive (many ... I think he didn't mean container being a protected object. ...
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  • Re: Multitasking and containers
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  • Re: Multitasking and containers
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