Debugging Clojure/Vagrant for 7 concurrency models in 7 weeks

gistfile1.txt

I am trying to replicate an example from this book: https://uk.bookshop.org/books/seven-concurrency-models-in-seven-weeks-when-threads-unravel/9781937785659

Running the below commands in a lein repl.

In the book, the second `parallel-sum` function executes 2.5x as fast as `sum` but on my Vagrant box (which has 4 cores, and demonstrates other parallelised code having a speed up effect) the two functions take pretty much the same time every time. My Vagrantfile is here https://github.com/annashipman/7weeks-concurrency/blob/main/Vagrantfile

This works in a non-Vagrant Clojure environment, i.e parallel-sum runs much faster.

So, what should I do differently in Vagrant to get it to work?


(ns sum.core
	(:require [clojure.core.reducers :as r]))
	
(defn sum [numbers]
 	(reduce + numbers))

(defn parallel-sum [numbers]
	(r/fold + numbers))

(def numbers (into [] (range 0 10000000)))

(time (sum numbers))

(time (sum numbers))

(time (parallel-sum numbers))

(time (parallel-sum numbers))

⚠️ The above examples are only ran 1 time each, I don't pretend to present any concurrency benchmarking, but demonstrate that GC impact is tremendous and can prevent to compare parallelism gains.