Implement RuntimeScheduler::getCurrentPriorityLevel

Summary:
Changelog: [internal]

Implement `RuntimeScheduler::getCurrentPriorityLevel`.

JavaScript implementation: https://github.com/facebook/react/blob/master/packages/scheduler/src/forks/SchedulerNoDOM.js#L63

Reviewed By: ShikaSD

Differential Revision: D27998510

fbshipit-source-id: 634c09185f9eae8f7afcdb6acd9b74effd587da7

ReactCommon/react/renderer/runtimescheduler/RuntimeScheduler.cpp

@@ -29,27 +29,28 @@ std::shared_ptr<Task> RuntimeScheduler::scheduleTask(
     isCallbackScheduled_ = true;
     runtimeExecutor_([this](jsi::Runtime &runtime) {
       isCallbackScheduled_ = false;
-
+      auto previousPriority = currentPriority_;
       while (!taskQueue_.empty()) {
-        auto topPriority = taskQueue_.top();
+        auto topPriorityTask = taskQueue_.top();
         auto now = now_();
-        auto didUserCallbackTimeout = topPriority->expirationTime <= now;
+        auto didUserCallbackTimeout = topPriorityTask->expirationTime <= now;
 
         if (!didUserCallbackTimeout && shouldYield_) {
           // This task hasn't expired and we need to yield.
           break;
         }
-
-        auto result = topPriority->execute(runtime);
+        currentPriority_ = topPriorityTask->priority;
+        auto result = topPriorityTask->execute(runtime);
 
         if (result.isObject() &&
             result.getObject(runtime).isFunction(runtime)) {
-          topPriority->callback =
+          topPriorityTask->callback =
               result.getObject(runtime).getFunction(runtime);
         } else {
           taskQueue_.pop();
         }
       }
+      currentPriority_ = previousPriority;
     });
   }
 
@@ -64,6 +65,10 @@ bool RuntimeScheduler::getShouldYield() const {
   return shouldYield_;
 }
 
+SchedulerPriority RuntimeScheduler::getCurrentPriorityLevel() const {
+  return currentPriority_;
+}
+
 RuntimeSchedulerTimePoint RuntimeScheduler::now() const {
   return now_();
 }

ReactCommon/react/renderer/runtimescheduler/RuntimeScheduler.h

@@ -31,6 +31,8 @@ class RuntimeScheduler final {
 
   bool getShouldYield() const;
 
+  SchedulerPriority getCurrentPriorityLevel() const;
+
   RuntimeSchedulerTimePoint now() const;
 
  private:
@@ -40,6 +42,7 @@ class RuntimeScheduler final {
       TaskPriorityComparer>
       taskQueue_;
   RuntimeExecutor const runtimeExecutor_;
+  SchedulerPriority currentPriority_{SchedulerPriority::NormalPriority};
   std::atomic_bool shouldYield_{false};
 
   /*

ReactCommon/react/renderer/runtimescheduler/RuntimeSchedulerBinding.cpp

@@ -133,6 +133,11 @@ jsi::Value RuntimeSchedulerBinding::get(
         });
   }
 
+  if (propertyName == "unstable_getCurrentPriorityLevel") {
+    auto currentPriorityLevel = runtimeScheduler_->getCurrentPriorityLevel();
+    return jsi::Value(runtime, serialize(currentPriorityLevel));
+  }
+
   if (propertyName == "unstable_ImmediatePriority") {
     return jsi::Value(runtime, serialize(SchedulerPriority::ImmediatePriority));
   }

ReactCommon/react/renderer/runtimescheduler/tests/RuntimeSchedulerTest.cpp

@@ -273,4 +273,43 @@ TEST_F(RuntimeSchedulerTest, continuationTask) {
   EXPECT_EQ(stubQueue_->size(), 0);
 }
 
+TEST_F(RuntimeSchedulerTest, getCurrentPriorityLevel) {
+  auto callback =
+      createHostFunctionFromLambda([this](bool didUserCallbackTimeout) {
+        EXPECT_EQ(
+            runtimeScheduler_->getCurrentPriorityLevel(),
+            SchedulerPriority::ImmediatePriority);
+        return jsi::Value::undefined();
+      });
+
+  EXPECT_EQ(
+      runtimeScheduler_->getCurrentPriorityLevel(),
+      SchedulerPriority::NormalPriority);
+
+  runtimeScheduler_->scheduleTask(
+      SchedulerPriority::ImmediatePriority, std::move(callback));
+
+  stubQueue_->tick();
+
+  EXPECT_EQ(
+      runtimeScheduler_->getCurrentPriorityLevel(),
+      SchedulerPriority::NormalPriority);
+
+  callback = createHostFunctionFromLambda([this](bool didUserCallbackTimeout) {
+    EXPECT_EQ(
+        runtimeScheduler_->getCurrentPriorityLevel(),
+        SchedulerPriority::IdlePriority);
+    return jsi::Value::undefined();
+  });
+
+  runtimeScheduler_->scheduleTask(
+      SchedulerPriority::IdlePriority, std::move(callback));
+
+  stubQueue_->tick();
+
+  EXPECT_EQ(
+      runtimeScheduler_->getCurrentPriorityLevel(),
+      SchedulerPriority::NormalPriority);
+}
+
 } // namespace facebook::react