QtConcurrent using Sequence generated on-the-fly
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Documentation and all examples I've seen assume that "Sequence ":http://qt-project.org/doc/qt-5/qtconcurrent.html#mapped (e.g. QList, QVector, etc.) is given in advance. That is, we know how many mapFunction() calls (and its' parameters) there will be beforehead.
Problem I am faced with is that new items that need to be proceded might emerge during the execution of QtConcurrent::mapped(). How can it be acheived?
I had an idea to inherit QFuture::const_iterator, override operators and use QtConcurrent::mapped(ConstIterator, ConstIterator, MapFunction) with ConstIterator being inherited class. Is it a good approach?
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Hi,
[quote author="AlexPo" date="1389308650"]Documentation and all examples I've seen assume that "Sequence ":http://qt-project.org/doc/qt-5/qtconcurrent.html#mapped (e.g. QList, QVector, etc.) is given in advance. That is, we know how many mapFunction() calls (and its' parameters) there will be in advance.[/quote]Yes, that is a fundamental assumption of the map/filter/reduce functions. Your container is expected to remain the same size at all times.
[quote]Problem I am faced with is that new items that need to be proceed might emerge *during * the execution of QtConcurrent::mapped(). How can it beforehead?[/quote]Would it be possible to do your processing in batches?
i.e. Call mapped() for a fixed-sized container. If any new items emerge, collect them in a new container. Then, run mapped() again. Repeat until there are no more new items.
[quote]I had an idea to inherit QFuture::const_iterator, override operators and use QtConcurrent::mapped(ConstIterator, ConstIterator, MapFunction) with ConstIterator being inherited class. Is it a good approach?[/quote]I wouldn't. For one thing, you will chang the meaning of const, and break the assumptions that Qt Concurrent makes.
Another possible approach is to subclass QRunnable instead. Create a QRunnable for each item to be processed. You can add new QRunnables to the thread pool on-the-fly. You can collect results by adding them to a mutex-protected shared container.
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Thanks for reply!
[quote author="JKSH" date="1389316006"]Would it be possible to do your processing in batches?
i.e. Call mapped() for a fixed-sized container. If any new items emerge, collect them in a new container. Then, run mapped() again. Repeat until there are no more new items.
[/quote]Yes, it would. But in my case that would be rather ugly design.
[quote author="JKSH" date="1389316006"]I wouldn't. For one thing, you will chang the meaning of const, and break the assumptions that Qt Concurrent makes.
Another possible approach is to subclass QRunnable instead. Create a QRunnable for each item to be processed. You can add new QRunnables to the thread pool on-the-fly. You can collect results by adding them to a mutex-protected shared container.[/quote]
I see. QRunnable then. Thanks again!
