`context.Context` is a standard way to carry:

• deadlines,
• cancellation signals,
• and request-scoped values

across API boundaries and between goroutines.

• Cancel work when a request is no longer needed (client disconnected, timeout, shutdown).
• Enforce timeouts/deadlines for I/O (HTTP calls, DB queries, RPC).
• Pass request-scoped metadata (trace IDs, request IDs) carefully.

• `context.Background()` — root context for main/service.
• `context.TODO()` — placeholder when you don’t have a context yet.
• `context.WithCancel(parent)` — manual cancellation.
• `context.WithTimeout(parent, d)` — cancel after duration.
• `context.WithDeadline(parent, t)` — cancel at specific time.
• `context.WithValue(parent, key, val)` — attach request-scoped values (use sparingly).

package main
 
import (
    "context"
    "time"
)
 
func main() {
    ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
    defer cancel()
 
    _ = ctx // pass ctx into HTTP/DB/RPC calls
}

package main
 
import (
    "context"
    "time"
)
 
func worker(ctx context.Context) {
    for {
        select {
        case <-ctx.Done():
            return
        default:
            time.Sleep(10 * time.Millisecond)
        }
    }
}
 
func main() {
    ctx, cancel := context.WithCancel(context.Background())
    go worker(ctx)
 
    time.Sleep(50 * time.Millisecond)
    cancel()
    time.Sleep(20 * time.Millisecond)
}

• Context is NOT for global configuration.
• Do NOT store large values in context; keep values small (IDs).
• Use typed keys to avoid collisions.
• Always call `cancel()` to release resources (timers) for timeout/deadline contexts.

• Goroutine
• http.Client
• http.Server

• deadline /ˈdedlaɪn/: hạn chót
• cancellation /ˌkænsəˈleɪʃən/: huỷ
• signal /ˈsɪɡnəl/: tín hiệu
• request-scoped /rɪˈkwest skoʊpt/: gắn với 1 request
• metadata /ˈmetəˌdeɪtə/: dữ liệu mô tả
• API boundary /ˌeɪ piː ˈaɪ ˈbaʊndri/: ranh giới API
• collision /kəˈlɪʒən/: xung đột
• sparingly /ˈsperɪŋli/: dùng hạn chế