Future Pattern in Go

future.go

package cacheutils

import (
	"sync"
	"time"
)

const FUTURETIMEOUT = 5 * time.Second

type Future interface {
	Get(string) interface{}
}

type StringFuture struct {
	sync.RWMutex
	inner map[string][]chan interface{}
	f     func(string) (interface{}, error)
}

func NewStringFuture(f func(string) (interface{}, error)) Future {
	sf := new(StringFuture)
	sf.RWMutex = sync.RWMutex{}
	sf.inner = make(map[string][]chan interface{})
	sf.f = f
	return sf
}

func (sf *StringFuture) Get(key string) interface{} {
	sf.Lock()
	_, ok := sf.inner[key]
	if ok {
		ch := make(chan interface{}, 1)
		sf.inner[key] = append(sf.inner[key], ch)
		sf.Unlock()
		ticker := time.NewTicker(FUTURETIMEOUT)
		defer ticker.Stop()
		select {
		case r :=<- ch:
			return r
		case <- ticker.C:
			return nil
		}
	} else {
		sf.inner[key] = make([]chan interface{}, 0, 4)
		sf.Unlock()

		res, err := sf.f(key)

		sf.Lock()
		chList := sf.inner[key]
		delete(sf.inner, key)
		sf.Unlock()
		if err != nil {
			go func() {
				for _, ch := range chList {
					ch <- res
				}
			}()
			return nil
		}
		go func() {
			for _, ch := range chList {
				ch <- res
			}
		}()
		return res
	}
}