# Multihreaded library inside ray actor

**URL:** <https://discuss.ray.io/t/multihreaded-library-inside-ray-actor/5661>\
**Category:** Ray Core\
**Created:** [April 4, 2022, 12:00am UTC](https://discuss.ray.io/t/multihreaded-library-inside-ray-actor/5661 "2022-04-04T00:00:35Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![marsupialtail](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/marsupialtail/32/1950_2.png) [@marsupialtail](https://discuss.ray.io/u/marsupialtail)\
**Post date:** [April 4, 2022, 12:00am UTC](https://discuss.ray.io/t/multihreaded-library-inside-ray-actor/5661/1 "2022-04-04T00:00:35Z")

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When I use numpy inside a ray actor, I notice that the numpy becomes single-core.

Is this expected behavior? When I use my numpy distribution in just Python I observe multi-core.

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**Author:** ![Mingwei](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/mingwei/32/997_2.png) [@Mingwei](https://discuss.ray.io/u/Mingwei)\
**Post date:** [April 4, 2022, 3:34pm UTC](https://discuss.ray.io/t/multihreaded-library-inside-ray-actor/5661/2 "2022-04-04T15:34:54Z")

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Is there a minimum script that can reproduce the behavior?

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**Author:** ![marsupialtail](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/marsupialtail/32/1950_2.png) [@marsupialtail](https://discuss.ray.io/u/marsupialtail)\
**Post date:** [April 4, 2022, 4:17pm UTC](https://discuss.ray.io/t/multihreaded-library-inside-ray-actor/5661/3 "2022-04-04T16:17:49Z")

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I discovered I can solve this problem by explicitly setting mkl.set\_num\_threads right before calling the numpy routine. I think there are some problems with default OS environ values inside ray actors

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**Author:** ![mannyv](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/mannyv/32/606_2.png) [@mannyv](https://discuss.ray.io/u/mannyv)\
**Post date:** [April 4, 2022, 6:51pm UTC](https://discuss.ray.io/t/multihreaded-library-inside-ray-actor/5661/4 "2022-04-04T18:51:53Z")

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Hi @marsupialtail,

I think that is intentional.

`https://github.com/ray-project/ray/blob/b3b1498eba171fe0e224dd3096c4c98156e2cbcf/python/ray/ __init__.py#L52`