package main

import (
    "fmt"
    "time"
)

// this is a worker that we will run in several parallel instances
// these workers will receive tasks through the 'jobs' channel and send the results to 'results'
// we will wait for one second for each task to simulate heavy requests
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() {
    // to use worker pool, we need to send a task and receive the execution results
    // therefore 2 channels are created
    jobs := make(chan int, 100)
    results := make(chan int, 100)

    // start 3 workers, initially blocked because no assignments yet
    for w := 1; w <= 3; w++ {
        go worker(w, jobs, results)
    }

    // send 5 jobs and then close the channel, notofying that all jobs have been sent
    for j := 1; j <= 5; j++ {
        jobs <- j
    }

    close(jobs)

    // collect all the results
    // this also ensures that the goroutines have ended
    for a := 1; a <= 5; a++ {
        <-results
    }
}