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[Fabric] Add lock for surface presenter observers #24052

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[Fabric] Add lock for surface presenter observers #24052

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7488361
[Fabric] Add lock for surface presenter observers
zhongwuzw Mar 20, 2019
5a19466
Replace std::mutex with better::shared_mutex
zhongwuzw Mar 21, 2019
45eb40d
Remove copy collection
zhongwuzw Mar 23, 2019
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20 changes: 15 additions & 5 deletions React/Fabric/RCTSurfacePresenter.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,7 @@ @implementation RCTSurfacePresenter {
RCTBridge *_bridge; // Unsafe. We are moving away from Bridge.
RCTBridge *_batchedBridge;
std::shared_ptr<const ReactNativeConfig> _reactNativeConfig;
std::mutex _observerListMutex;
better::shared_mutex _observerListMutex;
NSMutableArray<id<RCTSurfacePresenterObserver>> *_observers;
}

Expand Down Expand Up @@ -315,13 +315,13 @@ - (void)schedulerOptimisticallyCreateComponentViewWithComponentHandle:(Component

- (void)addObserver:(id<RCTSurfacePresenterObserver>)observer
{
std::lock_guard<std::mutex> lock(_observerListMutex);
std::unique_lock<better::shared_mutex> lock(_observerListMutex);
[self->_observers addObject:observer];
}

- (void)removeObserver:(id<RCTSurfacePresenterObserver>)observer
{
std::lock_guard<std::mutex> lock(_observerListMutex);
std::unique_lock<better::shared_mutex> lock(_observerListMutex);
[self->_observers removeObject:observer];
}

Expand All @@ -331,7 +331,12 @@ - (void)mountingManager:(RCTMountingManager *)mountingManager willMountComponent
{
RCTAssertMainQueue();

for (id<RCTSurfacePresenterObserver> observer in _observers) {
NSArray<id<RCTSurfacePresenterObserver>> *observers;
{
std::shared_lock<better::shared_mutex> lock(_observerListMutex);
observers = [_observers copy];
}
for (id<RCTSurfacePresenterObserver> observer in observers) {
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Why not iterate over _observers while the lock is acquired?

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One thing to watch out for is deadlock if any of the observer delegate methods can add/remove observers unless better::shared_mutex is like recursive_mutex.

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@shergin What I concerned is the same as @ide , we have no control what delegate would do. But if this deadlock situation shouldn't happened. I can remove copy.

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willMountComponentsWithRootTag: is being called quite often and perf sensitive, so please do.

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Done!

if ([observer respondsToSelector:@selector(willMountComponentsWithRootTag:)]) {
[observer willMountComponentsWithRootTag:rootTag];
}
Expand All @@ -351,7 +356,12 @@ - (void)mountingManager:(RCTMountingManager *)mountingManager didMountComponents
surface.view.rootView = (RCTSurfaceRootView *)rootComponentView;
}
}
for (id<RCTSurfacePresenterObserver> observer in _observers) {
NSArray<id<RCTSurfacePresenterObserver>> *observers;
{
std::shared_lock<better::shared_mutex> lock(_observerListMutex);
observers = [_observers copy];
}
for (id<RCTSurfacePresenterObserver> observer in observers) {
if ([observer respondsToSelector:@selector(didMountComponentsWithRootTag:)]) {
[observer didMountComponentsWithRootTag:rootTag];
}
Expand Down