add generic memory pressure listener interface

Reviewed By: lexs

Differential Revision: D2989071

fb-gh-sync-id: 375c7551bd4b281096850732432f016c2684add0
shipit-source-id: 375c7551bd4b281096850732432f016c2684add0

ReactAndroid/src/main/java/com/facebook/react/MemoryPressureRouter.java

@@ -2,7 +2,9 @@
 
 package com.facebook.react;
 
-import javax.annotation.Nullable;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.Set;
 
 import android.annotation.TargetApi;
 import android.app.Activity;
@@ -11,9 +13,8 @@ import android.content.Context;
 import android.content.res.Configuration;
 import android.os.Build;
 
-import com.facebook.react.bridge.CatalystInstance;
 import com.facebook.react.bridge.MemoryPressure;
-import com.facebook.react.bridge.ReactContext;
+import com.facebook.react.bridge.MemoryPressureListener;
 
 import static android.content.ComponentCallbacks2.TRIM_MEMORY_BACKGROUND;
 import static android.content.ComponentCallbacks2.TRIM_MEMORY_MODERATE;
@@ -27,7 +28,8 @@ public class MemoryPressureRouter {
   // am start -a "com.facebook.catalyst.ACTION_TRIM_MEMORY" --activity-single-top -n <activity>
   private static final String ACTION_TRIM_MEMORY ="com.facebook.catalyst.ACTION_TRIM_MEMORY";
 
-  private @Nullable CatalystInstance mCatalystInstance;
+  private final Set<MemoryPressureListener> mListeners =
+    Collections.synchronizedSet(new LinkedHashSet<MemoryPressureListener>());
   private final ComponentCallbacks2 mCallbacks = new ComponentCallbacks2() {
     @Override
     public void onTrimMemory(int level) {
@@ -60,12 +62,18 @@ public class MemoryPressureRouter {
     context.getApplicationContext().registerComponentCallbacks(mCallbacks);
   }
 
-  public void onNewReactContextCreated(ReactContext reactContext) {
-    mCatalystInstance = reactContext.getCatalystInstance();
+  /**
+   * Add a listener to be notified of memory pressure events.
+   */
+  public void addMemoryPressureListener(MemoryPressureListener listener) {
+    mListeners.add(listener);
   }
 
-  public void onReactInstanceDestroyed() {
-    mCatalystInstance = null;
+  /**
+   * Remove a listener previously added with {@link #addMemoryPressureListener}.
+   */
+  public void removeMemoryPressureListener(MemoryPressureListener listener) {
+    mListeners.remove(listener);
   }
 
   public void destroy(Context context) {
@@ -81,8 +89,12 @@ public class MemoryPressureRouter {
   }
 
   private void dispatchMemoryPressure(MemoryPressure level) {
-    if (mCatalystInstance != null) {
-      mCatalystInstance.handleMemoryPressure(level);
+    // copy listeners array to avoid ConcurrentModificationException if any of the listeners remove
+    // themselves in handleMemoryPressure()
+    MemoryPressureListener[] listeners =
+      mListeners.toArray(new MemoryPressureListener[mListeners.size()]);
+    for (MemoryPressureListener listener : listeners) {
+      listener.handleMemoryPressure(level);
     }
   }
 

ReactAndroid/src/main/java/com/facebook/react/ReactInstanceManagerImpl.java

@@ -715,7 +715,7 @@ import static com.facebook.react.bridge.ReactMarkerConstants.RUN_JS_BUNDLE_START
 
     catalystInstance.initialize();
     mDevSupportManager.onNewReactContextCreated(reactContext);
-    mMemoryPressureRouter.onNewReactContextCreated(reactContext);
+    mMemoryPressureRouter.addMemoryPressureListener(catalystInstance);
     moveReactContextToCurrentLifecycleState();
 
     for (ReactRootView rootView : mAttachedRootViews) {
@@ -772,7 +772,7 @@ import static com.facebook.react.bridge.ReactMarkerConstants.RUN_JS_BUNDLE_START
     }
     reactContext.destroy();
     mDevSupportManager.onReactInstanceDestroyed(reactContext);
-    mMemoryPressureRouter.onReactInstanceDestroyed();
+    mMemoryPressureRouter.removeMemoryPressureListener(reactContext.getCatalystInstance());
   }
 
   /**

ReactAndroid/src/main/java/com/facebook/react/bridge/CatalystInstance.java

@@ -21,7 +21,7 @@ import com.facebook.proguard.annotations.DoNotStrip;
  * Java APIs be invokable from JavaScript as well.
  */
 @DoNotStrip
-public interface CatalystInstance {
+public interface CatalystInstance extends MemoryPressureListener {
   void runJSBundle();
   // This is called from java code, so it won't be stripped anyway, but proguard will rename it,
   // which this prevents.
@@ -48,8 +48,6 @@ public interface CatalystInstance {
   <T extends NativeModule> T getNativeModule(Class<T> nativeModuleInterface);
   Collection<NativeModule> getNativeModules();
 
-  void handleMemoryPressure(MemoryPressure level);
-
   /**
    * Adds a idle listener for this Catalyst instance. The listener will receive notifications
    * whenever the bridge transitions from idle to busy and vice-versa, where the busy state is

ReactAndroid/src/main/java/com/facebook/react/bridge/MemoryPressureListener.java

@@ -0,0 +1,15 @@
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+package com.facebook.react.bridge;
+
+/**
+ * Listener interface for memory pressure events.
+ */
+public interface MemoryPressureListener {
+
+  /**
+   * Called when the system generates a memory warning.
+   */
+  void handleMemoryPressure(MemoryPressure level);
+
+}