Master Golang: Worker Pools

In this example we’ll look at how to implement a worker pool using goroutines and channels.
	package main
	import ( "fmt" "time" )
Here’s the worker, of which we’ll run several concurrent instances. These workers will receive work on the `jobs` channel and send the corresponding results on `results`. We’ll sleep a second per job to simulate an expensive task.	func worker(id int, jobs <-chan int, results chan<- int) { for j := range jobs { fmt.Println("worker", id, "started job", j) time.Sleep(time.Second) fmt.Println("worker", id, "finished job", j) results <- j * 2 } }
	func main() {
In order to use our pool of workers we need to send them work and collect their results. We make 2 channels for this.	const numJobs = 5 jobs := make(chan int, numJobs) results := make(chan int, numJobs)
This starts up 3 workers, initially blocked because there are no jobs yet.	for w := 1; w <= 3; w++ { go worker(w, jobs, results) }
Here we send 5 `jobs` and then `close` that channel to indicate that’s all the work we have.	for j := 1; j <= numJobs; j++ { jobs <- j } close(jobs)
Finally we collect all the results of the work. This also ensures that the worker goroutines have finished. An alternative way to wait for multiple goroutines is to use a WaitGroup.	for a := 1; a <= numJobs; a++ { <-results } }

Our running program shows the 5 jobs being executed by various workers. The program only takes about 2 seconds despite doing about 5 seconds of total work because there are 3 workers operating concurrently.

$ time go run worker-pools.go 
worker 1 started  job 1
worker 2 started  job 2
worker 3 started  job 3
worker 1 finished job 1
worker 1 started  job 4
worker 2 finished job 2
worker 2 started  job 5
worker 3 finished job 3
worker 1 finished job 4
worker 2 finished job 5

real    0m2.358s

Next example: WaitGroups.