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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](waitgroups).
    
	for a := 1; a <= numJobs; a++ {

    






    
    
		<-results

    
worker 3 started  job 1
worker 2 started  job 3
worker 1 started  job 2
worker 1 finished job 2
worker 1 started  job 4
worker 2 finished job 3
worker 2 started  job 5
worker 3 finished job 1
worker 1 finished job 4
worker 2 finished job 5







    
    
	}

    
worker 2 started  job 3
worker 2 started  job 4
worker 1 finished job 2
worker 1 started  job 5
worker 2 finished job 4
worker 1 finished job 5







    
    
}

    
worker 1 started  job 2
worker 3 started  job 5
worker 1 finished job 2
worker 3 finished job 5







    
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