ensureRootIsScheduled() — react Function Reference

Source Code

packages/react-reconciler/src/ReactFiberRootScheduler.js lines 116–152

export function ensureRootIsScheduled(root: FiberRoot): void {
  // This function is called whenever a root receives an update. It does two
  // things 1) it ensures the root is in the root schedule, and 2) it ensures
  // there's a pending microtask to process the root schedule.
  //
  // Most of the actual scheduling logic does not happen until
  // `scheduleTaskForRootDuringMicrotask` runs.

  // Add the root to the schedule
  if (root === lastScheduledRoot || root.next !== null) {
    // Fast path. This root is already scheduled.
  } else {
    if (lastScheduledRoot === null) {
      firstScheduledRoot = lastScheduledRoot = root;
    } else {
      lastScheduledRoot.next = root;
      lastScheduledRoot = root;
    }
  }

  // Any time a root received an update, we set this to true until the next time
  // we process the schedule. If it's false, then we can quickly exit flushSync
  // without consulting the schedule.
  mightHavePendingSyncWork = true;

  ensureScheduleIsScheduled();

  if (
    __DEV__ &&
    !disableLegacyMode &&
    ReactSharedInternals.isBatchingLegacy &&
    root.tag === LegacyRoot
  ) {
    // Special `act` case: Record whenever a legacy update is scheduled.
    ReactSharedInternals.didScheduleLegacyUpdate = true;
  }
}