How do you safely use a map from multiple goroutines in Go?

Go maps are not safe for concurrent use. The runtime detects concurrent map access and throws a fatal error: 'concurrent map read and map write'. There are three main solutions, each with different performance trade-offs.

// BUGGY: concurrent map access — runtime fatal error
var m = map[string]int{}
for i := 0; i < 100; i++ {
    go func(n int) {
        m[fmt.Sprint(n)] = n // RACE: concurrent write
    }(i)
}

// SOLUTION 1: sync.Mutex protecting a regular map
type SafeMap struct {
    mu sync.RWMutex
    m  map[string]int
}
func (s *SafeMap) Set(k string, v int) {
    s.mu.Lock(); defer s.mu.Unlock()
    s.m[k] = v
}
func (s *SafeMap) Get(k string) (int, bool) {
    s.mu.RLock(); defer s.mu.RUnlock()
    v, ok := s.m[k]
    return v, ok
}

// SOLUTION 2: sync.Map (optimised for read-heavy / disjoint-key patterns)
var sm sync.Map
sm.Store("key", 42)
val, ok := sm.Load("key")
sm.Delete("key")
sm.Range(func(k, v any) bool {
    fmt.Println(k, v)
    return true // return false to stop
})

// SOLUTION 3: actor model — single goroutine owns the map
type op struct{ key string; val int; resp chan int }
opCh := make(chan op)
go func() {
    m := map[string]int{}
    for o := range opCh {
        m[o.key] = o.val
        if o.resp != nil { o.resp <- m[o.key] }
    }
}()

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