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`sync.Mutex` is a mutual exclusion lock used to protect shared data from concurrent access.

• Prevent data races when multiple goroutines read/write the same variable/structure.
• Protect critical sections (a block of code that must not run concurrently).

• You have shared mutable state (e.g., map, slice, struct fields) accessed by multiple goroutines.
• You need simple, explicit locking around updates.

package main
 
import "sync"
 
type Counter struct {
    mu sync.Mutex
    n  int
}
 
func (c *Counter) Inc() {
    c.mu.Lock()
    c.n++
    c.mu.Unlock()
}
 
func (c *Counter) Value() int {
    c.mu.Lock()
    defer c.mu.Unlock()
    return c.n
}

• Always `Unlock()` (use `defer` for safety).
• Avoid long work while holding the lock (it reduces throughput).
• Do NOT copy a struct containing a `Mutex` after first use.

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

• mutex /ˈmjuːtɛks/: khóa loại trừ
• mutual exclusion /ˈmjuːtʃuəl ɪkˈskluːʒən/: loại trừ lẫn nhau
• shared data /ʃerd ˈdeɪtə/: dữ liệu dùng chung
• concurrent /kənˈkɝːənt/: đồng thời
• critical section /ˈkrɪtɪkəl ˈsekʃən/: vùng code cần khóa
• pitfall /ˈpɪtfɔːl/: “bẫy” thường gặp
• throughput /ˈθruːpʊt/: thông lượng

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