Function entangleAsyncAction

packages/react-reconciler/src/ReactFiberAsyncAction.js:71–101

(
  transition: Transition,
  thenable: Thenable<S>,
)

let needsIsomorphicIndicator: boolean = false;

export function entangleAsyncAction<S>(
  transition: Transition,
  thenable: Thenable<S>,
): Thenable<S> {
  // `thenable` is the return value of the async action scope function. Create
  // a combined thenable that resolves once every entangled scope function
  // has finished.
  if (currentEntangledListeners === null) {
    // There's no outer async action scope. Create a new one.
    const entangledListeners = (currentEntangledListeners = []);
    currentEntangledPendingCount = 0;
    currentEntangledLane = requestTransitionLane(transition);
    const entangledThenable: Thenable<void> = {
      status: 'pending',
      value: undefined,
      then(resolve: void => mixed) {
        entangledListeners.push(resolve);
      },
    };
    currentEntangledActionThenable = entangledThenable;
    if (enableDefaultTransitionIndicator) {
      needsIsomorphicIndicator = true;
      // We'll check if we need a default indicator in a microtask. Ensure
      // we have this scheduled even if no root is scheduled.
      ensureScheduleIsScheduled();
    }
  }
  currentEntangledPendingCount++;
  thenable.then(pingEngtangledActionScope, pingEngtangledActionScope);
  return thenable;
}

function pingEngtangledActionScope() {
  if (--currentEntangledPendingCount === 0) {