Limit the size of LruBitmapPool/MemoryCache when app is in background

When an app is moved to background, onTrimMemory() will be called, and
LruBitmapPool/MemoryCache will be trimmed. However, the app could keep
running and bitmaps will be retired to MemoryCache and LruBitmapPool.

This change allows limit of the sizes of LruBitmapPool/MemoryCache (by
MemoryCategory) when the app is in background, and restore the sizes
to normal when it's moved out of background.

Author: Eric Miao

library/src/main/java/com/bumptech/glide/Glide.java

@@ -1,10 +1,12 @@
 package com.bumptech.glide;
 
 import android.app.Activity;
+import android.app.Application;
 import android.content.ComponentCallbacks2;
 import android.content.Context;
 import android.content.res.Configuration;
 import android.graphics.Bitmap;
+import android.os.Bundle;
 import android.os.MessageQueue.IdleHandler;
 import android.util.Log;
 import android.view.View;
@@ -50,7 +52,7 @@
  * RequestBuilder} and maintaining an {@link Engine}, {@link BitmapPool}, {@link
  * com.bumptech.glide.load.engine.cache.DiskCache} and {@link MemoryCache}.
  */
-public class Glide implements ComponentCallbacks2 {
+public class Glide implements ComponentCallbacks2, Application.ActivityLifecycleCallbacks {
   private static final String DEFAULT_DISK_CACHE_DIR = "image_manager_disk_cache";
   private static final String DESTROYED_ACTIVITY_WARNING =
       "You cannot start a load on a not yet attached View or a Fragment where getActivity() "
@@ -77,6 +79,8 @@ public class Glide implements ComponentCallbacks2 {
   private final RequestOptionsFactory defaultRequestOptionsFactory;
   private MemoryCategory memoryCategory = MemoryCategory.NORMAL;
 
+  private final MemoryCategory memoryCategoryInBackground;
+
   @GuardedBy("this")
   @Nullable
   private BitmapPreFiller bitmapPreFiller;
@@ -205,7 +209,9 @@ public static void enableHardwareBitmaps() {
   public static void tearDown() {
     synchronized (Glide.class) {
       if (glide != null) {
-        glide.getContext().getApplicationContext().unregisterComponentCallbacks(glide);
+        Application application = (Application) glide.getContext().getApplicationContext();
+	application.unregisterActivityLifecycleCallbacks(glide);
+        application.unregisterComponentCallbacks(glide);
         glide.engine.shutdown();
       }
       glide = null;
@@ -224,7 +230,7 @@ private static void initializeGlide(
       @NonNull Context context,
       @NonNull GlideBuilder builder,
       @Nullable GeneratedAppGlideModule annotationGeneratedModule) {
-    Context applicationContext = context.getApplicationContext();
+    Application applicationContext = (Application) context.getApplicationContext();
     List<GlideModule> manifestModules = Collections.emptyList();
     if (annotationGeneratedModule == null || annotationGeneratedModule.isManifestParsingEnabled()) {
       manifestModules = new ManifestParser(applicationContext).parse();
@@ -265,6 +271,7 @@ private static void initializeGlide(
     }
     Glide glide = builder.build(applicationContext, manifestModules, annotationGeneratedModule);
     applicationContext.registerComponentCallbacks(glide);
+    applicationContext.registerActivityLifecycleCallbacks(glide);
     Glide.glide = glide;
   }
 
@@ -332,6 +339,11 @@ private static void throwIncorrectGlideModule(Exception e) {
     this.connectivityMonitorFactory = connectivityMonitorFactory;
     this.defaultRequestOptionsFactory = defaultRequestOptionsFactory;
 
+    GlideBuilder.MemoryCategoryInBackground memoryCategoryInBackground =
+        experiments.get(GlideBuilder.MemoryCategoryInBackground.class);
+    this.memoryCategoryInBackground = memoryCategoryInBackground != null ?
+                                      memoryCategoryInBackground.value() : null;
+
     // This has a circular relationship with Glide and GlideContext in that it depends on both,
     // but it's created by Glide's constructor. In practice this shouldn't matter because the
     // supplier holding the registry should never be initialized before this constructor finishes.
@@ -446,6 +458,8 @@ public void clearMemory() {
     arrayPool.clearMemory();
   }
 
+  private boolean inBackground = false;
+
   /**
    * Clears some memory with the exact amount depending on the given level.
    *
@@ -678,6 +692,12 @@ void unregisterRequestManager(RequestManager requestManager) {
   @Override
   public void onTrimMemory(int level) {
     trimMemory(level);
+    // when level is TRIM_MEMORY_UI_HIDDEN or higher, it indicates that the app
+    // is in the background, limit the memory usage by set memory category
+    if (memoryCategoryInBackground != null && level >= TRIM_MEMORY_UI_HIDDEN) {
+      inBackground = true;
+      setMemoryCategory(memoryCategoryInBackground);
+    }
   }
 
   @Override
@@ -697,4 +717,47 @@ public interface RequestOptionsFactory {
     @NonNull
     RequestOptions build();
   }
+
+  /**
+   * Any activity that is started or resumed indicates that the app is no longer
+   * in the background, and the memory category needs to be restored
+   */
+  @Override
+  public void onActivityStarted(Activity activity) {
+    if (memoryCategoryInBackground != null && inBackground) {
+      setMemoryCategory(MemoryCategory.NORMAL);
+    }
+  }
+
+  @Override
+  public void onActivityResumed(Activity activity) {
+    if (memoryCategoryInBackground != null && inBackground) {
+      setMemoryCategory(MemoryCategory.NORMAL);
+    }
+  }
+
+  @Override
+  public void onActivityCreated(Activity activity, Bundle savedIntsanceState) {
+    // Do nothing.
+  }
+
+  @Override
+  public void onActivityDestroyed(Activity activity) {
+    // Do nothing.
+  }
+
+  @Override
+  public void onActivityStopped(Activity activity) {
+    // Do nothing.
+  }
+
+  @Override
+  public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
+    // Do nothing.
+  }
+
+  @Override
+  public void onActivityPaused(Activity activity) {
+    // Do nothing.
+  }
 }

library/src/main/java/com/bumptech/glide/GlideBuilder.java

@@ -539,6 +539,15 @@ public GlideBuilder setDisableHardwareBitmapsOnO(boolean disableHardwareBitmapsO
     return this;
   }
 
+  /**
+   * This method sets the memory category when the app is in the background
+   */
+  public GlideBuilder setMemoryCategoryInBackground(@Nullable MemoryCategory category) {
+    glideExperimentsBuilder.update(new MemoryCategoryInBackground(category),
+                                   category != null ? true : false);
+    return this;
+  }
+
   void setRequestManagerFactory(@Nullable RequestManagerFactory factory) {
     this.requestManagerFactory = factory;
   }
@@ -653,4 +662,16 @@ public static final class OverrideGlideThreadPriority implements Experiment {}
 
   /** See {@link #setUseMediaStoreOpenFileApisIfPossible(boolean)}. */
   public static final class UseMediaStoreOpenFileApisIfPossible implements Experiment {}
+
+  public static final class MemoryCategoryInBackground implements Experiment {
+    private final MemoryCategory category;
+
+    public MemoryCategoryInBackground(MemoryCategory category) {
+      this.category = category;
+    }
+
+    public MemoryCategory value() {
+      return this.category;
+    }
+  }
 }

library/src/main/java/com/bumptech/glide/MemoryCategory.java

@@ -2,6 +2,10 @@
 
 /** An enum for dynamically modifying the amount of memory Glide is able to use. */
 public enum MemoryCategory {
+  /**
+   * Tells Glide's memory cache and bitmap pool to use no memory
+   */
+  ZERO(0.0f),
   /**
    * Tells Glide's memory cache and bitmap pool to use at most half of their initial maximum size.
    */