===== WithCancel =====

==== What is it? ====
`context.WithCancel(parent)` creates a child context that can be canceled manually by calling the returned `cancel()` function.

Signature:
`ctx, cancel := context.WithCancel(parent)`

==== What is it used for? ====
  * Stop background goroutines when you’re done.
  * Cancel a group of tasks if one fails.
  * Implement graceful shutdown logic.

==== Example ====
<code go>
ctx, cancel := context.WithCancel(context.Background())
go func() {
    <-ctx.Done()
    // cleanup or stop work
}()
cancel()
</code>

==== Notes / pitfalls ====
  * Always call `cancel()` to release resources.
  * Cancellation propagates: canceling parent cancels children.
  * Use `select { case <-ctx.Done(): ... }` inside goroutines.

==== Related pages ====
  * [[go:concurrency:context|context.Context]]
  * [[go:concurrency:withtimeout|WithTimeout]]
  * [[go:concurrency:withdeadline|WithDeadline]]

==== Hard words (English) ====
  * **manual** /ˈmænjuəl/: thủ công
  * **cleanup** /ˈkliːnʌp/: dọn dẹp tài nguyên
  * **propagate** /ˈprɑːpəɡeɪt/: truyền tiếp
  * **graceful shutdown** /ˈɡreɪsfəl ˈʃʌtdaʊn/: tắt êm