packages/redux-saga/src/internal/proc.js
function cancelMain() {
    if (mainTask.isRunning && !mainTask.isCancelled) {
      mainTask.isCancelled = true
      next(TASK_CANCEL)
    }
  }
function cancelMain() {
    if (mainTask.isRunning && !mainTask.isCancelled) {
      mainTask.isCancelled = true
      next(TASK_CANCEL)
    }
  }
cancellation of the main task. We'll simply resume the Generator with a Cancel