Fix: Measure expiration times relative to module initialization (#15357)

We use bitwise operations to compute expiration times, which means they
need to be smaller than 31 bits. So we measure times relative to module
initialization, similar to `performance.now`.

This was already working in the old fiber scheduler, but we didn't have
a test for it.

packages/react-reconciler/src/ReactFiberScheduler.new.js

@@ -228,20 +228,21 @@ let interruptedBy: Fiber | null = null;
 // In other words, because expiration times determine how updates are batched,
 // we want all updates of like priority that occur within the same event to
 // receive the same expiration time. Otherwise we get tearing.
+let initialTimeMs: number = now();
 let currentEventTime: ExpirationTime = NoWork;
 
 export function requestCurrentTime() {
  if (workPhase === RenderPhase || workPhase === CommitPhase) {
  // We're inside React, so it's fine to read the actual time.
- return msToExpirationTime(now());
+ return msToExpirationTime(now() - initialTimeMs);
  }
  // We're not inside React, so we may be in the middle of a browser event.
  if (currentEventTime !== NoWork) {
  // Use the same start time for all updates until we enter React again.
  return currentEventTime;
  }
  // This is the first update since React yielded. Compute a new start time.
- currentEventTime = msToExpirationTime(now());
+ currentEventTime = msToExpirationTime(now() - initialTimeMs);
  return currentEventTime;
 }
 

packages/react-reconciler/src/__tests__/ReactExpiration-test.internal.js

@@ -245,4 +245,31 @@ describe('ReactExpiration', () => {
  '1 [D] [render]',
  ]);
  });
+
+ it('should measure expiration times relative to module initialization', () => {
+ // Tests an implementation detail where expiration times are computed using
+ // bitwise operations.
+
+ jest.resetModules();
+ Scheduler = require('scheduler');
+ // Before importing the renderer, advance the current time by a number
+ // larger than the maximum allowed for bitwise operations.
+ const maxSigned31BitInt = 1073741823;
+ Scheduler.advanceTime(maxSigned31BitInt * 100);
+
+ // Now import the renderer. On module initialization, it will read the
+ // current time.
+ ReactNoop = require('react-noop-renderer');
+
+ ReactNoop.render('Hi');
+
+ // The update should not have expired yet.
+ expect(Scheduler).toFlushExpired([]);
+ expect(ReactNoop).toMatchRenderedOutput(null);
+
+ // Advance the time some more to expire the update.
+ Scheduler.advanceTime(10000);
+ expect(Scheduler).toFlushExpired([]);
+ expect(ReactNoop).toMatchRenderedOutput('Hi');
+ });
 });