Fabric: MessageQueueEventBeat

Summary:
@public
MessageQueueEventBeat implements particular Event Beat synchronized with Message Queue and calling a callback on the JS thread (aka Message Queue thread). The actual beat is synchronized with the main run loop.

Reviewed By: mdvacca

Differential Revision: D8886230

fbshipit-source-id: 97ef7d10f705789b4b0cd3a12389db960159f289

React/Fabric/Utils/MessageQueueEventBeat.h

@@ -0,0 +1,35 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <CoreFoundation/CoreFoundation.h>
+#include <CoreFoundation/CFRunLoop.h>
+#include <cxxreact/MessageQueueThread.h>
+#include <fabric/events/EventBeat.h>
+
+namespace facebook {
+namespace react {
+
+/*
+ * Event beat that associated with MessageQueueThread.
+ */
+class MessageQueueEventBeat:
+  public EventBeat {
+
+public:
+  MessageQueueEventBeat(const std::shared_ptr<MessageQueueThread> &messageQueueThread);
+  ~MessageQueueEventBeat();
+
+  void induce() const override;
+
+private:
+  const std::shared_ptr<MessageQueueThread> messageQueueThread_;
+  CFRunLoopObserverRef mainRunLoopObserver_;
+  mutable std::atomic<bool> isBusy_ {false};
+};
+
+} // namespace react
+} // namespace facebook

React/Fabric/Utils/MessageQueueEventBeat.mm

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+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include "MessageQueueEventBeat.h"
+
+namespace facebook {
+namespace react {
+
+MessageQueueEventBeat::MessageQueueEventBeat(const std::shared_ptr<MessageQueueThread> &messageQueueThread):
+  messageQueueThread_(messageQueueThread) {
+
+  mainRunLoopObserver_ =
+    CFRunLoopObserverCreateWithHandler(
+      NULL /* allocator */,
+      kCFRunLoopBeforeWaiting /* activities */,
+      true /* repeats */,
+      0 /* order */,
+      ^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
+        // Note: We only `induce` beat here; actual beat will be performed on
+        // a different thread.
+        this->induce();
+      }
+  );
+
+  assert(mainRunLoopObserver_);
+
+  CFRunLoopAddObserver(CFRunLoopGetMain(), mainRunLoopObserver_, kCFRunLoopCommonModes);
+}
+
+MessageQueueEventBeat::~MessageQueueEventBeat() {
+  CFRunLoopRemoveObserver(CFRunLoopGetMain(), mainRunLoopObserver_, kCFRunLoopCommonModes);
+  CFRelease(mainRunLoopObserver_);
+}
+
+void MessageQueueEventBeat::induce() const {
+  if (!isRequested_ || isBusy_) {
+    return;
+  }
+
+  isBusy_ = true;
+  messageQueueThread_->runOnQueue([this]() {
+    this->beat();
+    isBusy_ = false;
+  });
+}
+
+} // namespace react
+} // namespace facebook