thoughts on a multithreaded version about is-prime HOT 3 OPEN

your worries of A race condition occurring will only be problematic when two or more threads that can access shared data and try to change it at the same time to different values. This does not need to be a problem as both threads should come to the same conclusion/write the same value.

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You can set each core to only handle multiples of each number except for multiples of 1. This way you can cover almost all the numbers. while having one core handle the numbers skipped by your other cores. probable max multithreaded efficiency use case will be to have about 10 cores dedicated to crunching numbers, after that multithreading will be too complicated to work.

This way you have one core handling any missed numbers, then second core handling multiples of 2, third core handling multiples of 3, fourth core handling multiples of 4, …and so on... up to core nine handling multiples of 9. This way all numbers get tested. Unfortunately some numbers will be tested more than once by different cores.

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cuda implementation uses more than 1000000 threads

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