Sleepsort and Concurrency in Golang

For me learning concurrency have always been tricky; Every language has a different way to handle/emulate concurrency, for example, old languages like Java uses Threads and modern languages like NodeJS and Python uses something called as event loops for its asynchronous IO which is there to make IO based things concurrent.

Recently I started diving deep into concurrency in Golang and I wanted to start with a good "Hello World" program for it. This time I thought of taking an unconventional way to write my first concurrent program. Going through various examples over the Internet I could not find anything that made it fun. I suddenly recalled Sleepsort and it was the ideal way (fun + new = <3) to learn concurrency.

The Concept

For people who do not know what Sleep Sort is, the basic goes something like this: spin n threads/co-routine (or whatever concurrent element the language has) for n numbers (to sort) and for each number x wait for time proportional to x (lets say x seconds) and then print/collect the number.

Implementation in Go

This is a very basic Implementation of Sleep Sort in Golang using Go Routines and WaitGroup.

// prints a number of sleeping for n seconds
func sleepAndPrint(x int, wg *sync.WaitGroup) {
    defer wg.Done()

    // Sleeping for time proportional to value
    time.Sleep(time.Duration(x) * time.Millisecond)

    // Printing the value

// Sorts given integer slice using sleep sort
func Sort(numbers []int) {
    var wg sync.WaitGroup

    // Creating wait group that waits of len(numbers) of go routines to finish

    for _, x := range numbers {
        // Spinning a Go routine
        go sleepAndPrint(x, &wg)

    // Waiting for all go routines to finish

I have published the code in a Github Repository. Feel free to fork and play around with it.

What else can you do with it

I encourage you to try it out, and trust me it is really fun to learn concurrency through this; Apart from running the basic sleep sort you should also try to do/learn with it. For example,

Concurrency essentials - Go Channels for inter go-routine communication - Mutex for synchronization making things routine-safe

You can also try to - collect the elements in a slice, in place of printing - make Sleep Sort handle negative numbers too - sort the numbers in descending order

If you find any interesting way to learn concurrency or any new use case here, please post a comment below. I would love to know them.

Arpit Bhayani

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