Go by Example: Worker Pools
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In this example we’ll look at how to implement a worker pool using goroutines and channels. |
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package main
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import "fmt"
import "time"
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Here’s the worker, of which we’ll run several
concurrent instances. These workers will receive
work on the |
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
}
}
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func main() {
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In order to use our pool of workers we need to send them work and collect their results. We make 2 channels for this. |
jobs := make(chan int, 100)
results := make(chan int, 100)
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This starts up 3 workers, initially blocked because there are no jobs yet. |
for w := 1; w <= 3; w++ {
go worker(w, jobs, results)
}
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Here we send 5 |
for j := 1; j <= 5; j++ {
jobs <- j
}
close(jobs)
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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 <= 5; a++ {
<-results
}
}
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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
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real 0m2.358s
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Next example: WaitGroups.