Fix incorrect application of idle priority in RuntimeScheduler (#45408)

Summary:
Pull Request resolved: #45408

Changelog: [General][Fixed] Fixed prioritization of idle priority tasks

We recently found out that idle priority tasks were never scheduled with the lowest priority possible. We didn't realize before because idle priority tasks weren't used, but now they are via `requestIdleCallback` and other mechanisms.

The problem was that the timeout for idle priority tasks was `std::chrono:milliseconds::max()`, and we compute the expiration time adding that to the current time. Doing that operation is always guaranteed to overflow, and the resulting expiration time was always in the past, resulting in the task having higher priority than any other tasks with any other priorities.

Instead of using `max()` we can just use a sensible value for idle priorities. In this case, 5 minutes should be more than enough.

Reviewed By: sammy-SC

Differential Revision: D59679513

fbshipit-source-id: 6c0f9e275818737ce804f05615c01f7ea6c126ab

packages/react-native/ReactCommon/react/renderer/runtimescheduler/RuntimeScheduler_Modern.cpp

@@ -24,7 +24,7 @@ std::chrono::milliseconds getResolvedTimeoutForIdleTask(
           timeoutForSchedulerPriority(SchedulerPriority::IdlePriority)
       ? timeoutForSchedulerPriority(SchedulerPriority::LowPriority) +
           customTimeout
-      : timeoutForSchedulerPriority(SchedulerPriority::IdlePriority);
+      : customTimeout;
 }
 } // namespace
 

packages/react-native/ReactCommon/react/renderer/runtimescheduler/SchedulerPriorityUtils.h

@@ -41,15 +41,15 @@ static inline std::chrono::milliseconds timeoutForSchedulerPriority(
     SchedulerPriority schedulerPriority) noexcept {
   switch (schedulerPriority) {
     case SchedulerPriority::ImmediatePriority:
-      return std::chrono::milliseconds(-1);
+      return std::chrono::milliseconds(0);
     case SchedulerPriority::UserBlockingPriority:
       return std::chrono::milliseconds(250);
     case SchedulerPriority::NormalPriority:
-      return std::chrono::milliseconds(5000);
+      return std::chrono::seconds(5);
     case SchedulerPriority::LowPriority:
-      return std::chrono::milliseconds(10'000);
+      return std::chrono::seconds(10);
     case SchedulerPriority::IdlePriority:
-      return std::chrono::milliseconds::max();
+      return std::chrono::minutes(5);
   }
 }
 

packages/react-native/ReactCommon/react/renderer/runtimescheduler/tests/RuntimeSchedulerTest.cpp

@@ -332,6 +332,71 @@ TEST_P(RuntimeSchedulerTest, scheduleTwoTasksWithDifferentPriorities) {
   EXPECT_EQ(hostFunctionCallCount_, 2);
 }
 
+TEST_P(RuntimeSchedulerTest, scheduleTwoTasksWithAllPriorities) {
+  uint idlePriorityTaskCallOrder = 0;
+  auto idlePriTask = createHostFunctionFromLambda(
+      [this, &idlePriorityTaskCallOrder](bool /*unused*/) {
+        idlePriorityTaskCallOrder = hostFunctionCallCount_;
+        return jsi::Value::undefined();
+      });
+
+  uint lowPriorityTaskCallOrder = 0;
+  auto lowPriTask = createHostFunctionFromLambda(
+      [this, &lowPriorityTaskCallOrder](bool /*unused*/) {
+        lowPriorityTaskCallOrder = hostFunctionCallCount_;
+        return jsi::Value::undefined();
+      });
+
+  uint normalPriorityTaskCallOrder = 0;
+  auto normalPriTask = createHostFunctionFromLambda(
+      [this, &normalPriorityTaskCallOrder](bool /*unused*/) {
+        normalPriorityTaskCallOrder = hostFunctionCallCount_;
+        return jsi::Value::undefined();
+      });
+
+  uint userBlockingPriorityTaskCallOrder = 0;
+  auto userBlockingPriTask = createHostFunctionFromLambda(
+      [this, &userBlockingPriorityTaskCallOrder](bool /*unused*/) {
+        userBlockingPriorityTaskCallOrder = hostFunctionCallCount_;
+        return jsi::Value::undefined();
+      });
+
+  uint immediatePriorityTaskCallOrder = 0;
+  auto immediatePriTask = createHostFunctionFromLambda(
+      [this, &immediatePriorityTaskCallOrder](bool /*unused*/) {
+        immediatePriorityTaskCallOrder = hostFunctionCallCount_;
+        return jsi::Value::undefined();
+      });
+
+  runtimeScheduler_->scheduleTask(
+      SchedulerPriority::IdlePriority, std::move(idlePriTask));
+  runtimeScheduler_->scheduleTask(
+      SchedulerPriority::LowPriority, std::move(lowPriTask));
+  runtimeScheduler_->scheduleTask(
+      SchedulerPriority::NormalPriority, std::move(normalPriTask));
+  runtimeScheduler_->scheduleTask(
+      SchedulerPriority::UserBlockingPriority, std::move(userBlockingPriTask));
+  runtimeScheduler_->scheduleTask(
+      SchedulerPriority::ImmediatePriority, std::move(immediatePriTask));
+
+  EXPECT_EQ(idlePriorityTaskCallOrder, 0);
+  EXPECT_EQ(lowPriorityTaskCallOrder, 0);
+  EXPECT_EQ(normalPriorityTaskCallOrder, 0);
+  EXPECT_EQ(userBlockingPriorityTaskCallOrder, 0);
+  EXPECT_EQ(immediatePriorityTaskCallOrder, 0);
+  EXPECT_EQ(stubQueue_->size(), 1);
+
+  stubQueue_->tick();
+
+  EXPECT_EQ(idlePriorityTaskCallOrder, 5);
+  EXPECT_EQ(lowPriorityTaskCallOrder, 4);
+  EXPECT_EQ(normalPriorityTaskCallOrder, 3);
+  EXPECT_EQ(userBlockingPriorityTaskCallOrder, 2);
+  EXPECT_EQ(immediatePriorityTaskCallOrder, 1);
+  EXPECT_EQ(stubQueue_->size(), 0);
+  EXPECT_EQ(hostFunctionCallCount_, 5);
+}
+
 TEST_P(RuntimeSchedulerTest, cancelTask) {
   bool didRunTask = false;
   auto callback = createHostFunctionFromLambda([&didRunTask](bool /*unused*/) {

packages/react-native/ReactCommon/react/renderer/runtimescheduler/tests/SchedulerPriorityTest.cpp

@@ -31,7 +31,7 @@ TEST(SchedulerPriorityTest, serialize) {
 TEST(SchedulerPriorityTest, timeoutForSchedulerPriority) {
   EXPECT_EQ(
       timeoutForSchedulerPriority(SchedulerPriority::ImmediatePriority),
-      std::chrono::milliseconds(-1));
+      std::chrono::milliseconds(0));
   EXPECT_EQ(
       timeoutForSchedulerPriority(SchedulerPriority::UserBlockingPriority),
       std::chrono::milliseconds(250));
@@ -43,5 +43,5 @@ TEST(SchedulerPriorityTest, timeoutForSchedulerPriority) {
       std::chrono::seconds(10));
   EXPECT_EQ(
       timeoutForSchedulerPriority(SchedulerPriority::IdlePriority),
-      std::chrono::milliseconds::max());
+      std::chrono::minutes(5));
 }