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`sync.RWMutex` is a read/write mutual exclusion lock. It allows multiple readers at the same time, but only one writer (and writers exclude readers).

• Protect shared data that is read very often but written less frequently.
• Improve throughput compared to `Mutex` in read-heavy workloads.

• Many goroutines read shared state, and updates are relatively rare.
• You can clearly separate “read” vs “write” sections.

package main
 
import "sync"
 
type Store struct {
    mu sync.RWMutex
    m  map[string]string
}
 
func (s *Store) Get(k string) (string, bool) {
    s.mu.RLock()
    defer s.mu.RUnlock()
    v, ok := s.m[k]
    return v, ok
}
 
func (s *Store) Set(k, v string) {
    s.mu.Lock()
    defer s.mu.Unlock()
    s.m[k] = v
}

• Use `RLock/RUnlock` for read-only sections; use `Lock/Unlock` for writes.
• Avoid “lock upgrade” patterns (RLock then Lock) — can cause deadlocks if done wrong.
• If writes are frequent, `RWMutex` may not be faster than `Mutex`.

• sync.Mutex
• Race detector (-race)

• read-heavy /ˈriːd ˈhevi/: đọc nhiều (ít ghi)
• throughput /ˈθruːpʊt/: thông lượng
• exclude /ɪkˈskluːd/: loại trừ, chặn
• deadlock /ˈdedlɑːk/: kẹt khóa