Mutexes

import "sync"
 
type SyncedData struct {
	inner map[string]int
	mutex sync.Mutex
}
 
func (s *SyncedData) Insert(k string, v int) {
	s.mutex.Lock()
	defer s.mutex.Unlock()
	s.inner[k] = v
}
 
func (s *SyncedData) Get(k string) int {
	s.mutex.Lock()
	defer s.mutex.Unlock()
	return s.inner[k]
}
 
// now these functions will work with multiple goroutines

Wait groups

increment a counter when a routine is added, decrement when it finishes

var wg sync.Waitgroup
 
sum := 0
for i := 0; i < 20; i++ {
	wg.Add(1)
	value += i
	go func() {
		defer wg.Done()
		sum += value
	}()
}
wg.Wait()
fmt.Println(sum)