inprogcache

main.go

package main

import (
	"fmt"
	"sync"
	"time"
)

var stopper chan bool // Semaphore.
var listeners []chan int

func main() {
	numWorkers := 5
	var wg sync.WaitGroup
	wg.Add(numWorkers)

	// We only want a single operation to go through
	// before all others block.
	stopper = make(chan bool, 1)
	defer close(stopper)
	listeners = make([]chan int, 0, numWorkers)

	// Perform 5 expensive operations concurrently!
	for i := 0; i < numWorkers; i++ {
		go func(w *sync.WaitGroup, workerID int) {
			defer wg.Done()
			resultChan := make(chan int)
			defer close(resultChan)
			listeners = append(listeners, resultChan)
			go scheduleWork(workerID)
			result := <-resultChan
			fmt.Printf("Worker %d received result %d\n", workerID, result)
		}(&wg, i)
	}

	wg.Wait()
}

func scheduleWork(workerID int) {
	// Notify the stopper channel that we are doing expensive work.
	stopper <- true
	result := performExpensiveWork(workerID)
	// Notify all workers that work is complete.
	for _, ll := range listeners {
		ll <- result
	}
}

func performExpensiveWork(workerID int) int {
	fmt.Printf("Worker %d: Doing expensive work\n", workerID)
	time.Sleep(time.Second)
	return 0
}