Exploring how to run a function x times concurrently and get the results on a new slice. Both with buffer and unbuffered channels.

concurrentFilter.go

package main

import (
	"fmt"
	"sync"
)

func filterBufferedChannel(toFilter []int) []int {
	filtered := make(chan int, len(toFilter))
	var wg sync.WaitGroup
	for i := 0; i < len(toFilter); i++ {
		wg.Add(1)
		fmt.Println("starting goroutine", i)
		go func(j int) {
			if toFilter[j]%2 == 0 {
				filtered <- toFilter[j]
			}
			wg.Done()
			fmt.Println("finishing goroutine", j)
		}(i)
	}
	wg.Wait()
	close(filtered)
	fmt.Println("reading values from channel")
	var slice []int
	for value := range filtered {
		slice = append(slice, value)
	}
	return slice
}

func filterUnbufferedChannel(toFilter []int) []int {
	filtered := make(chan int)
	var wg sync.WaitGroup
	for i := 0; i < len(toFilter); i++ {
		wg.Add(1)
		fmt.Println("starting goroutine", i)
		go func(j int) {
			if toFilter[j]%2 == 0 {
				filtered <- toFilter[j]
			}
			wg.Done()
			fmt.Println("finishing goroutine", j)
		}(i)
	}
	go func() {
		wg.Wait()
		close(filtered)
	}()
	fmt.Println("reading values from channel")
	var slice []int
	for value := range filtered {
		slice = append(slice, value)
	}
	return slice
}

func main() {
	sliceToFilter := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}
	filteredSlice := filterBufferedChannel(sliceToFilter)
	fmt.Println("filtered slice", filteredSlice)
	// filteredSlice = filterUnbufferedChannel(sliceToFilter)
	// fmt.Println("filtered slice", filteredSlice)
}