如何在Go中gc互斥锁映射？

Question

I am making a cache wrapper around a database. To account for possibly slow database calls, I was thinking of a mutex per key (pseudo Go code):

mutexes = map[string]*sync.Mutex // instance variable

mutexes[key].Lock()
defer mutexes[key].Unlock()

if value, ok := cache.find(key); ok {
   return value
}
value = databaseCall(key)
cache.save(key, value)
return value

However I don't want my map to grow too much. My cache is an LRU and I want to have a fixed size for some other reasons not mentioned here. I would like to do something like

delete(mutexes, key)

when all the locks on the key are over but... that doesn't look thread safe to me... How should I do it?

Note: I found this question In Go, can we synchronize each key of a map using a lock per key? but no answer

Answer 1

I wrote a simple similar implementation: mapmutex

But instead of a map of mutexes, in this implementation, a mutex is used to guard the map and each item in the map is used like a 'lock'. The map itself is just simple ordinary map.