mirror of
https://github.com/facebook/react-native.git
synced 2025-11-01 09:14:26 +00:00
Valentin Shergin
934275f931
Summary:
This changes the way we throttle `onLayout` events in Fabric.
The approach we used before has several issues:
* Every event-dispatching action initiated a lambda scheduled on JavaScript thread (which is a bit inefficient).
* If an event had {0,0,0,0} frame, it might be skipped because this is the default frame value.
* An event was always delivered by the exact block scheduled at the moment of the event initiation (even though some other blocks might be called before). In case of events being initiated rapidly, it can delay actual event delivery and maybe even overwhelm the JavaScript thread.
The new implementation uses a different approach: we maintain the shared storage with recent frame value and use the very first opportunity to deliver it. Alse see comments in the code.
Changelog: [Internal] Fabric-specific internal change.
Reviewed By: sammy-SC
Differential Revision: D25676336
fbshipit-source-id: 275b08990f7c5cf1f05a8f954ebc795a14e10ec2
74 lines
1.7 KiB
C++
74 lines
1.7 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*/
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#pragma once
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#include <memory>
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#include <mutex>
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#include <react/renderer/core/LayoutMetrics.h>
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#include <react/renderer/core/ReactPrimitives.h>
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#include "TouchEventEmitter.h"
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namespace facebook {
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namespace react {
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class ViewEventEmitter;
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using SharedViewEventEmitter = std::shared_ptr<const ViewEventEmitter>;
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class ViewEventEmitter : public TouchEventEmitter {
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public:
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using TouchEventEmitter::TouchEventEmitter;
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#pragma mark - Accessibility
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void onAccessibilityAction(const std::string &name) const;
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void onAccessibilityTap() const;
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void onAccessibilityMagicTap() const;
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void onAccessibilityEscape() const;
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#pragma mark - Layout
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void onLayout(const LayoutMetrics &layoutMetrics) const;
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private:
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/*
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* Contains the most recent `frame` and a `mutex` protecting access to it.
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*/
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struct LayoutEventState {
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/*
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* Protects an access to other fields of the struct.
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*/
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std::mutex mutex;
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/*
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* Last dispatched `frame` value or value that's being dispatched right now.
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*/
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Rect frame{};
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/*
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* Indicates that the `frame` value was already dispatched (and dispatching
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* of the *same* value is not needed).
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*/
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bool wasDispatched{false};
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/*
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* Indicates that some lambda is already being dispatching (and dispatching
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* another one is not needed).
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*/
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bool isDispatching{false};
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};
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mutable std::shared_ptr<LayoutEventState> layoutEventState_{
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std::make_shared<LayoutEventState>()};
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};
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} // namespace react
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} // namespace facebook
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