mirror of
https://github.com/facebook/react-native.git
synced 2025-11-01 09:14:26 +00:00
Andres Suarez
8bd3edec88
Reviewed By: aaronabramov Differential Revision: D33367752 fbshipit-source-id: 4ce94d184485e5ee0a62cf67ad2d3ba16e285c8f
92 lines
3.0 KiB
C++
92 lines
3.0 KiB
C++
/*
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* Copyright (c) Meta Platforms, Inc. and 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 <jsi/jsi.h>
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#include <atomic>
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#include <functional>
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#include <memory>
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namespace facebook {
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namespace react {
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/*
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* Event Beat serves two interleaving purposes: synchronization of event queues
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* and ensuring that event dispatching happens on proper threads.
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*/
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class EventBeat {
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public:
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/*
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* The concept of `Owner`
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* The purpose of `EventBeat` is handling an asynchronous callback to itself
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* which is being delivered on some different thread. That brings a challenge
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* of ensuring that the `EventBeat` object stays valid during the timeframe of
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* callback execution. The concept of Owner helps with that. The owner is a
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* shared pointer that retains (probably indirectly) the `EventBeat` object.
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* To ensure the correctness of the call, `EventBeat` retains the owner
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* (practically creating a retain cycle) during executing the callback. In
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* case if the pointer to the owner already null, `EventBeat` skips executing
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* the callback. It's impossible to retain itself directly or refer to the
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* shared pointer to itself from a constructor. `OwnerBox` is designed to work
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* around this issue; it allows to store the pointer later, right after the
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* creation of some other object that owns an `EventBeat`.
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*/
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using Owner = std::weak_ptr<void const>;
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struct OwnerBox {
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Owner owner;
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};
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using SharedOwnerBox = std::shared_ptr<OwnerBox>;
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using Factory =
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std::function<std::unique_ptr<EventBeat>(SharedOwnerBox const &ownerBox)>;
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using BeatCallback = std::function<void(jsi::Runtime &runtime)>;
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EventBeat(SharedOwnerBox ownerBox);
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virtual ~EventBeat() = default;
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/*
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* Communicates to the Beat that a consumer is waiting for the coming beat.
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* A consumer must request coming beat after the previous beat happened
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* to receive a next coming one.
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*/
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virtual void request() const;
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/*
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* Induces the next beat to happen as soon as possible. If the method
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* is called on the proper thread, the beat must happen synchronously.
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* Subclasses might override this method to implement specific
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* out-of-turn beat scheduling.
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* Some types of Event Beats do not support inducing, hence the default
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* implementation does nothing.
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* Receiver might ignore the call if a beat was not requested.
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*/
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virtual void induce() const;
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/*
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* Sets the beat callback function.
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* The callback is must be called on the proper thread.
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*/
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void setBeatCallback(BeatCallback beatCallback);
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protected:
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/*
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* Should be used by sublasses to send a beat.
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* Receiver might ignore the call if a beat was not requested.
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*/
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void beat(jsi::Runtime &runtime) const;
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BeatCallback beatCallback_;
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SharedOwnerBox ownerBox_;
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mutable std::atomic<bool> isRequested_{false};
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};
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} // namespace react
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} // namespace facebook
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