Mutex when reading from a map?

Question

go

I'm writing a simple session store...

import "sync"

type Session struct {...}

type SessionStorage struct {                                             
    sync.Mutex
    sessions map[string]Session
    ...
}

func (s *SessionStorage) Get(id string) (Session, bool) {
    s.Lock()
    v, ok := s.sessions[id]
    s.Unlock()
    return v, ok
}

func (s *SessionStorage) Set(id string, session Session) {
    s.Lock()
    s.sessions[id] = session
    s.Unlock()
}
...

I have a question. Do I need to synchronize the read from the map ( method Get(...)), or is it an atomic operation in Go?

Answer 1

You need RWMutex https://pkg.go.dev/sync#RWMutex Read only, no write at all, not guaranteed by spec, but thread safe in current implementation. If write is expected, you also need RWMutex.