westonpace commented on a change in pull request #9995:
URL: https://github.com/apache/arrow/pull/9995#discussion_r612480026
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File path: cpp/src/arrow/util/async_generator.h
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@@ -1332,4 +1332,49 @@ Result<Iterator<T>> MakeReadaheadIterator(Iterator<T>
it, int readahead_queue_si
return MakeGeneratorIterator(std::move(owned_bg_generator));
}
+/// \brief Make a generator that returns a single pre-generated future
Review comment:
The atomic index in VectorGenerator is not needed (mistake on my part).
The mutex in MappingGenerator is neccesary. Async reentrant means that the
`operator()()` method may be called before the future previously returned has
completed but only after the last call to `operator()()` completed.
So, for example, in MappingGenerator the state is modified by future
callbacks. These future callbacks run after the call to `operator()()`
completed so it's possible they will be called at the same time as the next
call to `operator()()`.
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