How does context.Context propagate cancellation across goroutines and calls?

Question

Accepted Answer

// Create contexts with cancellation, timeout, or deadline
ctx, cancel := context.WithCancel(context.Background())
defer cancel() // always call cancel to release resources

ctx2, cancel2 := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel2()

ctx3, cancel3 := context.WithDeadline(context.Background(), time.Now().Add(10*time.Second))
defer cancel3()

// Passing ctx through the call chain
func handleRequest(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context() // already has request-scoped cancellation

user, err := userService.GetUser(ctx, userID)
    if err != nil {
        // if ctx was cancelled (client disconnected), err wraps context.Canceled
        if errors.Is(err, context.Canceled) {
            return // client gone, no need to respond
        }
        http.Error(w, err.Error(), 500)
        return
    }
    json.NewEncoder(w).Encode(user)
}

func (s *UserService) GetUser(ctx context.Context, id string) (*User, error) {
    // Pass ctx to DB query — cancellation propagates to DB driver
    return s.repo.FindByID(ctx, id)
}

// Attach values to context (use sparingly)
type ctxKey string
const requestIDKey ctxKey = "requestID"

ctx = context.WithValue(ctx, requestIDKey, "req-123")
reqID := ctx.Value(requestIDKey).(string) Pass context as the first parameter — never store it in a struct Always call the cancel function returned by WithCancel/WithTimeout — even if the operation completes Use context.WithValue only for request-scoped metadata (trace IDs, auth tokens) — not for optional parameters Respect ctx.Done() in goroutines: select on it alongside work channels Check ctx.Err() to distinguish context.Canceled from context.DeadlineExceeded

How does context.Context propagate cancellation across goroutines and calls?

Context forms a tree where cancellation propagates from parent to all children. Every function that may block or do I/O should accept a ctx as its first parameter and respect its cancellation.

How does context.Context propagate cancellation across goroutines and calls?

Context forms a tree where cancellation propagates from parent to all children. Every function that may block or do I/O should accept a ctx as its first parameter and respect its cancellation.

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