parallel map not parallel about rayon HOT 6 CLOSED

@russel Examples of weight usage and of weight_max usage can be found in the benchmarks and also in the demos[1, 2].

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Rayon knows how to split the collection, but it's still an open question to decide when to split. See #81 and this discussion on the users forum.

Try adding a weight call to tune this, or force the finest granularity with weight_max.

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@cuviper Hummm… I was assuming Java/Stream/ForkJoin type thing. Do you have an example of idiomatic use rather than the reference to the API documentation?

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@lilianmoraru Thanks for those pointers. Those codes have shown me some things about other crates as well as about Rayon. :-)

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.weight_max()

does the job as needed.

To avoid violations of the Principal of Least Surprise I wonder if this "maximal parallelism" is a better default that the "keep it sequential" currently in place> After all the name of the function is par_iter.

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FWIW, the current default is not "keep it sequential." Rather, the current default weight is 1.0, and the internal threshold for splitting is 10240.0. So if your total collection is smaller than that, then yes it will run fully sequentially. That threshold is rather arbitrary, which is why we're talking about ways to improve the default experience. I don't think "maximal parallelism" will be the right answer either, but if you want to join the conversation, please visit the links I gave earlier.

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