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Consider using our own PRNG in rayon-core #570

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cuviper opened this issue Apr 27, 2018 · 0 comments
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Consider using our own PRNG in rayon-core #570

cuviper opened this issue Apr 27, 2018 · 0 comments

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@cuviper
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cuviper commented Apr 27, 2018

We have a kludge in .travis.yml to deal with rand and its rustc compatibility. It would be nice to do better here.

We currently use rand in two ways:

  • Some tests use randomized input, often seeded.
  • Worker threads randomize which other threads they try to steal from.

We only run tests on nightly right now (barring #536), so only the use by worker threads matters for rustc compatibility in general. We use rand::weak_rng() for that, but it would probably be just fine to implement a simple PRNG locally. Then we could get rid of the compatibility kludge, and just keep rand as a dev-dependency.

FWIW, rand is also reconsidering its compatibility story in rust-random/rand#413.
@cuviper cuviper mentioned this issue Apr 30, 2018
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bors bot added a commit that referenced this issue Jun 5, 2018
@bors @cuviper
Merge #571
dea6b10 
571: Implement our own PRNG for rayon-core r=nikomatsakis a=cuviper

Our need for randomness is very simple, just to spread the work-stealing
somewhat equally across all possible victims.  Rather than worrying
about compatibility and updates to the `rand` crate, we now implement a
simple `xorshift*` generator for this.  We keep `rand` only as a dev-
dependency for testing purposes.

Closes #570.

Co-authored-by: Josh Stone <cuviper@gmail.com>
@bors bors bot closed this as completed in #571 Jun 5, 2018
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