From 183d1f42edecb9e303c05d1a4303d17ecffb0cc0 Mon Sep 17 00:00:00 2001
From: Andrew Clark <git@andrewclark.io>
Date: Mon, 8 Apr 2019 19:44:06 -0700
Subject: [PATCH] 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.
---
 .../src/ReactFiberScheduler.new.js            |  5 ++--
 .../ReactExpiration-test.internal.js          | 27 +++++++++++++++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/packages/react-reconciler/src/ReactFiberScheduler.new.js b/packages/react-reconciler/src/ReactFiberScheduler.new.js
index c86bd58ce6a57..26a2e12ed1d90 100644
--- a/packages/react-reconciler/src/ReactFiberScheduler.new.js
+++ b/packages/react-reconciler/src/ReactFiberScheduler.new.js
@@ -228,12 +228,13 @@ 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) {
@@ -241,7 +242,7 @@ export function requestCurrentTime() {
     return currentEventTime;
   }
   // This is the first update since React yielded. Compute a new start time.
-  currentEventTime = msToExpirationTime(now());
+  currentEventTime = msToExpirationTime(now() - initialTimeMs);
   return currentEventTime;
 }
 
diff --git a/packages/react-reconciler/src/__tests__/ReactExpiration-test.internal.js b/packages/react-reconciler/src/__tests__/ReactExpiration-test.internal.js
index 8001a8d2c96c6..9a9402ecb90d2 100644
--- a/packages/react-reconciler/src/__tests__/ReactExpiration-test.internal.js
+++ b/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');
+  });
 });