Why is a mutex needed in a rate limiter? Can the problem be solved without a mutex, using sync.Map?

Mutex (mutual exclusion) in a rate limiter is needed to protect shared data from concurrent access by multiple goroutines, to prevent data races and incorrect request counting.

For example, if multiple goroutines update the request counter simultaneously, without a mutex, an incorrect value may be obtained.

Using sync.Map helps avoid locks during read and write operations on the map, but does not guarantee atomicity of complex operations such as incrementing a counter. Therefore, additional synchronization (e.g., mutex or atomic operations) is necessary to solve the problem.

Example:

 type RateLimiter struct {
     mu sync.Mutex
     requests map[string]int
 }

 func (r *RateLimiter) Allow(key string) bool {
     r.mu.Lock()
     defer r.mu.Unlock()
     count := r.requests[key]
     if count >= 10 {
         return false
     }
     r.requests[key] = count + 1
     return true
 }

If using sync.Map, additional synchronization or atomic operations are still required for atomic updates, otherwise race conditions may occur.