mirror of
https://github.com/facebook/react-native.git
synced 2025-11-01 09:14:26 +00:00
Valentin Shergin
c80192c2ab
Summary: The purpose of `EventBeat` is handling an asynchronous callback to itself which is being delivered on some different thread. That brings a challenge of ensuring that the `EventBeat` object stays valid during the timeframe of callback execution. The concept of Owner helps with that. The owner is a shared pointer that retains (probably indirectly) the `EventBeat` object. To ensure the correctness of the call, `EventBeat` retains the owner (practically creating a retain cycle) during executing the callback. In case if the pointer to the owner already null, `EventBeat` skips executing the callback. It's impossible to retain itself directly or refer to the shared pointer to itself from a constructor. `OwnerBox` is designed to work around this issue; it allows to store the pointer later, right after the creation of some other object that owns an `EventBeat`. Reviewed By: JoshuaGross Differential Revision: D17128549 fbshipit-source-id: 7ed34fd865430975157fd362f51c4a3d64214430
87 lines
2.0 KiB
Plaintext
87 lines
2.0 KiB
Plaintext
// Copyright (c) Facebook, Inc. and its affiliates.
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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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#import "MainRunLoopEventBeat.h"
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#import <React/RCTUtils.h>
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#import <mutex>
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namespace facebook {
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namespace react {
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MainRunLoopEventBeat::MainRunLoopEventBeat(EventBeat::SharedOwnerBox const &ownerBox, RuntimeExecutor runtimeExecutor)
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: EventBeat(ownerBox), runtimeExecutor_(std::move(runtimeExecutor))
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{
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mainRunLoopObserver_ = CFRunLoopObserverCreateWithHandler(
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NULL /* allocator */,
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kCFRunLoopBeforeWaiting /* activities */,
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true /* repeats */,
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0 /* order */,
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^(CFRunLoopObserverRef observer, CFRunLoopActivity activity) {
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if (!this->isRequested_) {
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return;
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}
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this->lockExecutorAndBeat();
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});
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assert(mainRunLoopObserver_);
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CFRunLoopAddObserver(CFRunLoopGetMain(), mainRunLoopObserver_, kCFRunLoopCommonModes);
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}
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MainRunLoopEventBeat::~MainRunLoopEventBeat()
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{
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CFRunLoopRemoveObserver(CFRunLoopGetMain(), mainRunLoopObserver_, kCFRunLoopCommonModes);
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CFRelease(mainRunLoopObserver_);
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}
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void MainRunLoopEventBeat::induce() const
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{
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if (!this->isRequested_) {
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return;
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}
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RCTExecuteOnMainQueue(^{
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this->lockExecutorAndBeat();
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});
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}
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void MainRunLoopEventBeat::lockExecutorAndBeat() const
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{
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auto owner = ownerBox_->owner.lock();
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if (!owner) {
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return;
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}
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// Note: We need the third mutex to get back to the main thread before
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// the lambda is finished (because all mutexes are allocated on the stack).
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std::mutex mutex1;
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std::mutex mutex2;
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std::mutex mutex3;
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mutex1.lock();
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mutex2.lock();
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mutex3.lock();
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jsi::Runtime *runtimePtr;
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runtimeExecutor_([&](jsi::Runtime &runtime) {
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runtimePtr = &runtime;
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mutex1.unlock();
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// `beat` is called somewhere here.
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mutex2.lock();
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mutex3.unlock();
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});
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mutex1.lock();
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beat(*runtimePtr);
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mutex2.unlock();
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mutex3.lock();
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}
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} // namespace react
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} // namespace facebook
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