`sync` is a Go standard library package that provides basic synchronization primitives for coordinating goroutines and protecting shared data.

• Protect shared resources from concurrent access (locks).
• Wait for multiple goroutines to finish.
• Run one-time initialization safely.
• Coordinate goroutines based on conditions.

• `Mutex`: mutual exclusion lock (one goroutine at a time).
• `RWMutex`: read/write lock (many readers or one writer).
• `WaitGroup`: wait for a set of goroutines to finish.
• `Once`: run a function exactly once.
• `Cond`: condition variable (wait/signal on state changes).
• `Map`: concurrent map (special use cases; read docs carefully).
• `Pool`: object pool to reduce allocations (advanced/perf).

var mu sync.Mutex
mu.Lock()
// critical section
mu.Unlock()

var mu sync.RWMutex
mu.RLock()
// read-only section
mu.RUnlock()
 
mu.Lock()
// write section
mu.Unlock()

var wg sync.WaitGroup
wg.Add(1)
go func() {
    defer wg.Done()
    // work
}()
wg.Wait()

var once sync.Once
once.Do(func() {
    // init exactly once
})

mu := sync.Mutex{}
cond := sync.NewCond(&mu)
_ = cond

• Use `sync.Mutex`/`RWMutex` when you have shared mutable state (maps/slices/struct fields).
• Use channels when you want to pass data between goroutines and structure concurrency as message passing.
• Both are valid; choose the clearest, safest design.

• Do NOT copy structs containing `Mutex`, `RWMutex`, `WaitGroup`, `Once`, or `Cond` after first use.
• Keep critical sections small (avoid slow I/O while holding locks).
• Prefer `context` for cancellation/timeouts; `sync` does not cancel goroutines.

• sync.Mutex
• sync.RWMutex
• sync.WaitGroup
• sync.Once
• sync.Cond
• sync/atomic
• Race detector (-race)

• synchronization /ˌsɪŋkrənəˈzeɪʃən/: đồng bộ hoá
• primitive /ˈprɪmətɪv/: thao tác/công cụ nền tảng
• coordinate /koʊˈɔːrdɪneɪt/: điều phối
• concurrent /kənˈkɝːənt/: đồng thời
• shared resource /ʃerd rɪˈzɔːrs/: tài nguyên dùng chung
• critical section /ˈkrɪtɪkəl ˈsekʃən/: vùng code cần khóa
• condition variable /kənˈdɪʃən ˈveriəbəl/: biến điều kiện
• allocation /ˌæləˈkeɪʃən/: cấp phát bộ nhớ
• mutable /ˈmjuːtəbəl/: có thể thay đổi
• message passing /ˈmesɪdʒ ˈpæsɪŋ/: truyền thông điệp
• cancellation /ˌkænsəˈleɪʃən/: huỷ