===== sync.RWMutex =====

==== What is it? ====
`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).

==== What is it used for? ====
  * Protect shared data that is read very often but written less frequently.
  * Improve throughput compared to `Mutex` in read-heavy workloads.

==== When to use ====
  * Many goroutines read shared state, and updates are relatively rare.
  * You can clearly separate "read" vs "write" sections.

==== Example ====
<code go>
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
}
</code>

==== Notes / pitfalls ====
  * 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`.

==== Related ====
  * [[go:concurrency:mutex|sync.Mutex]]
  * [[go:concurrency:race_detector|Race detector (-race)]]

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