Add experiment to clean up resources when the app is backgrounded

Summary:
Changelog: [internal]

Setup an experiment to measure impact of releasing resources when the app enters background.

Reviewed By: JoshuaGross, shergin

Differential Revision: D25952690

fbshipit-source-id: acfaa4a1689cc03c6020fdee62d3594859c9da3d

React/Base/RCTConstants.h

@@ -28,3 +28,9 @@ RCT_EXTERN void RCTExperimentSetOptimizedHitTesting(BOOL value);
  */
 RCT_EXTERN BOOL RCTExperimentGetPreemptiveViewAllocationDisabled(void);
 RCT_EXTERN void RCTExperimentSetPreemptiveViewAllocationDisabled(BOOL value);
+
+/*
+ * Release resources when app enters background
+ */
+RCT_EXTERN BOOL RCTExperimentGetReleaseResourcesWhenBackgrounded(void);
+RCT_EXTERN void RCTExperimentSetReleaseResourcesWhenBackgrounded(BOOL value);

React/Base/RCTConstants.m

@@ -54,3 +54,18 @@ void RCTExperimentSetPreemptiveViewAllocationDisabled(BOOL value)
 {
   RCTExperimentPreemptiveViewAllocationDisabled = value;
 }
+
+/*
+ * Release resources when app enters background
+ */
+static BOOL RCTExperimentReleaseResourcesWhenBackgrounded = NO;
+
+BOOL RCTExperimentGetReleaseResourcesWhenBackgrounded()
+{
+  return RCTExperimentReleaseResourcesWhenBackgrounded;
+}
+
+void RCTExperimentSetReleaseResourcesWhenBackgrounded(BOOL value)
+{
+  RCTExperimentReleaseResourcesWhenBackgrounded = value;
+}

React/CxxBridge/RCTCxxBridge.mm

@@ -13,6 +13,7 @@
 #import <React/RCTBridge.h>
 #import <React/RCTBridgeMethod.h>
 #import <React/RCTBridgeModule.h>
+#import <React/RCTConstants.h>
 #import <React/RCTConvert.h>
 #import <React/RCTCxxBridgeDelegate.h>
 #import <React/RCTCxxModule.h>
@@ -292,6 +293,10 @@ struct RCTInstanceCallback : public InstanceCallback {
                                              selector:@selector(handleMemoryWarning)
                                                  name:UIApplicationDidReceiveMemoryWarningNotification
                                                object:nil];
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(handleApplicationDidEnterBackgroundNotification)
+                                                 name:UIApplicationDidEnterBackgroundNotification
+                                               object:nil];
   }
   return self;
 }
@@ -350,6 +355,26 @@ struct RCTInstanceCallback : public InstanceCallback {
   }
 }
 
+- (void)handleApplicationDidEnterBackgroundNotification
+{
+  if (!RCTExperimentGetReleaseResourcesWhenBackgrounded()) {
+    return;
+  }
+
+  // We only want to run garbage collector when the loading is finished
+  // and the instance is valid.
+  if (!_valid || _loading) {
+    return;
+  }
+
+  // We need to hold a local retaining pointer to react instance
+  // in case if some other tread resets it.
+  auto reactInstance = _reactInstance;
+  if (reactInstance) {
+    reactInstance->handleMemoryPressure(40 /* TRIM_MEMORY_BACKGROUND */);
+  }
+}
+
 /**
  * Ensure block is run on the JS thread. If we're already on the JS thread, the block will execute synchronously.
  * If we're not on the JS thread, the block is dispatched to that thread. Any errors encountered while executing

React/Fabric/Mounting/RCTComponentViewRegistry.mm

@@ -35,6 +35,10 @@ const NSInteger RCTComponentViewRegistryRecyclePoolMaxSize = 1024;
                                              selector:@selector(handleApplicationDidReceiveMemoryWarningNotification)
                                                  name:UIApplicationDidReceiveMemoryWarningNotification
                                                object:nil];
+    [[NSNotificationCenter defaultCenter] addObserver:self
+                                             selector:@selector(handleApplicationDidEnterBackgroundNotification)
+                                                 name:UIApplicationDidEnterBackgroundNotification
+                                               object:nil];
 
     dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
       // Calling this a bit later, when the main thread is probably idle while JavaScript thread is busy.
@@ -162,4 +166,11 @@ const NSInteger RCTComponentViewRegistryRecyclePoolMaxSize = 1024;
   _recyclePool.clear();
 }
 
+- (void)handleApplicationDidEnterBackgroundNotification
+{
+  if (RCTExperimentGetReleaseResourcesWhenBackgrounded()) {
+    _recyclePool.clear();
+  }
+}
+
 @end

React/Fabric/RCTSurfacePresenter.mm

@@ -333,6 +333,10 @@ static BackgroundExecutor RCTGetBackgroundExecutor()
     RCTExperimentSetPreemptiveViewAllocationDisabled(YES);
   }
 
+  if (reactNativeConfig && reactNativeConfig->getBool("react_fabric:release_resources_when_backgrounded_ios")) {
+    RCTExperimentSetReleaseResourcesWhenBackgrounded(YES);
+  }
+
   auto componentRegistryFactory =
       [factory = wrapManagedObject(_mountingManager.componentViewRegistry.componentViewFactory)](
           EventDispatcher::Weak const &eventDispatcher, ContextContainer::Shared const &contextContainer) {