Function createChildAbortController

src/utils/abortController.ts:68–99

(
  parent: AbortController,
  maxListeners?: number,
)

 * @returns Child AbortController
 */
export function createChildAbortController(
  parent: AbortController,
  maxListeners?: number,
): AbortController {
  const child = createAbortController(maxListeners)

  // Fast path: parent already aborted, no listener setup needed
  if (parent.signal.aborted) {
    child.abort(parent.signal.reason)
    return child
  }

  // WeakRef prevents the parent from keeping an abandoned child alive.
  // If all strong references to child are dropped without aborting it,
  // the child can still be GC'd — the parent only holds a dead WeakRef.
  const weakChild = new WeakRef(child)
  const weakParent = new WeakRef(parent)
  const handler = propagateAbort.bind(weakParent, weakChild)

  parent.signal.addEventListener('abort', handler, { once: true })

  // Auto-cleanup: remove parent listener when child is aborted (from any source).
  // Both parent and handler are weakly held — if either has been GC'd or the
  // parent already aborted ({once: true}), the cleanup is a harmless no-op.
  child.signal.addEventListener(
    'abort',
    removeAbortHandler.bind(weakParent, new WeakRef(handler)),
    { once: true },
  )

  return child
}