Simple goroutines wrapper to provide Scala-like futures functionality in Golang. Adapted from: http://labs.strava.com/blog/futures-in-golang/

future.go

package main

import (
	"errors"
	"time"
)

type FutureFunction func() (interface{}, error)
type FutureResult func(timeout ...time.Duration) (interface{}, error)

func Future(f FutureFunction) FutureResult {
	var result interface{}
	var err error

	c := make(chan struct{}, 1)

	go func() {
		defer close(c)
		result, err = f()
	}()

	return func(timeout ...time.Duration) (interface{}, error) {
		if len(timeout) == 1 {
			select {
			case <-c:
				return result, err
			case <-time.After(timeout[0]):
				return nil, errors.New("Future timeout")
			}
		} else {
			<-c
			return result, err
		}
	}
}

main.go

package main

import (
	"fmt"
	"time"
)

func DoLongProcessing() (interface{}, error) {
	time.Sleep(time.Second * 5)
	return 123, nil
}

func printResults(res interface{}, err error, start time.Duration, waiting time.Duration) {
	if err != nil {
		fmt.Printf("Error: '%s', %v since start, total wait time for this function: %v\n", err, start, waiting)
	} else {
		fmt.Printf("Success: '%d', %v since start, total wait time for this function: %v\n", res, start, waiting)
	}
}

func main() {
	start := time.Now()

	future := Future(DoLongProcessing)

	waiting := time.Now()
	var res, err = future(time.Millisecond * 500)
	printResults(res, err, time.Since(start), time.Since(waiting))

	waiting = time.Now()
	res, err = future()
	printResults(res, err, time.Since(start), time.Since(waiting))

	waiting = time.Now()
	res, err = future()
	printResults(res, err, time.Since(start), time.Since(waiting))
}

output.txt

> go run .\main.go .\futures.go
Error: 'Future timeout', 500.1081ms since start, total wait time for this function: 500.1081ms
Success: '123', 5.0002842s since start, total wait time for this function: 4.5001761s
Success: '123', 5.0002842s since start, total wait time for this function: 0s