Move FlutterLoader disk I/O to a background thread to comply with Android strict mode

Fixes flutter/flutter#56145

Author: jason-simmons

shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java

@@ -22,6 +22,9 @@
 import io.flutter.view.VsyncWaiter;
 import java.io.File;
 import java.util.*;
+import java.util.concurrent.Callable;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
 
 /** Finds Flutter resources in an application APK and also loads Flutter's native library. */
 public class FlutterLoader {
@@ -76,10 +79,29 @@ public static FlutterLoader getInstance() {
   }
 
   private boolean initialized = false;
-  @Nullable private ResourceExtractor resourceExtractor;
   @Nullable private Settings settings;
   private long initStartTimestampMillis;
 
+  private static class InitResult {
+    final String appStoragePath;
+    final String engineCachesPath;
+    final String dataDirPath;
+    final ResourceExtractor resourceExtractor;
+
+    private InitResult(
+        String appStoragePath,
+        String engineCachesPath,
+        String dataDirPath,
+        ResourceExtractor resourceExtractor) {
+      this.appStoragePath = appStoragePath;
+      this.engineCachesPath = engineCachesPath;
+      this.dataDirPath = dataDirPath;
+      this.resourceExtractor = resourceExtractor;
+    }
+  }
+
+  @Nullable Future<InitResult> initResultFuture;
+
   /**
    * Starts initialization of the native system.
    *
@@ -110,18 +132,32 @@ public void startInitialization(@NonNull Context applicationContext, @NonNull Se
     }
 
     // Ensure that the context is actually the application context.
-    applicationContext = applicationContext.getApplicationContext();
+    final Context appContext = applicationContext.getApplicationContext();
 
     this.settings = settings;
 
     initStartTimestampMillis = SystemClock.uptimeMillis();
-    initResources(applicationContext);
 
-    System.loadLibrary("flutter");
-
-    VsyncWaiter.getInstance(
-            (WindowManager) applicationContext.getSystemService(Context.WINDOW_SERVICE))
+    VsyncWaiter.getInstance((WindowManager) appContext.getSystemService(Context.WINDOW_SERVICE))
         .init();
+
+    // Use a background thread for initialization tasks that require disk access.
+    Callable<InitResult> initTask =
+        new Callable<InitResult>() {
+          @Override
+          public InitResult call() {
+            ResourceExtractor resourceExtractor = initResources(appContext);
+
+            System.loadLibrary("flutter");
+
+            return new InitResult(
+                PathUtils.getFilesDir(appContext),
+                PathUtils.getCacheDirectory(appContext),
+                PathUtils.getDataDirectory(appContext),
+                resourceExtractor);
+          }
+        };
+    initResultFuture = Executors.newSingleThreadExecutor().submit(initTask);
   }
 
   /**
@@ -146,8 +182,10 @@ public void ensureInitializationComplete(
           "ensureInitializationComplete must be called after startInitialization");
     }
     try {
-      if (resourceExtractor != null) {
-        resourceExtractor.waitForCompletion();
+      InitResult result = initResultFuture.get();
+
+      if (result.resourceExtractor != null) {
+        result.resourceExtractor.waitForCompletion();
       }
 
       List<String> shellArgs = new ArrayList<>();
@@ -166,8 +204,7 @@ public void ensureInitializationComplete(
 
       String kernelPath = null;
       if (BuildConfig.DEBUG || BuildConfig.JIT_RELEASE) {
-        String snapshotAssetPath =
-            PathUtils.getDataDirectory(applicationContext) + File.separator + flutterAssetsDir;
+        String snapshotAssetPath = result.dataDirPath + File.separator + flutterAssetsDir;
         kernelPath = snapshotAssetPath + File.separator + DEFAULT_KERNEL_BLOB;
         shellArgs.add("--" + SNAPSHOT_ASSET_PATH_KEY + "=" + snapshotAssetPath);
         shellArgs.add("--" + VM_SNAPSHOT_DATA_KEY + "=" + vmSnapshotData);
@@ -187,20 +224,18 @@ public void ensureInitializationComplete(
                 + aotSharedLibraryName);
       }
 
-      shellArgs.add("--cache-dir-path=" + PathUtils.getCacheDirectory(applicationContext));
+      shellArgs.add("--cache-dir-path=" + result.engineCachesPath);
       if (settings.getLogTag() != null) {
         shellArgs.add("--log-tag=" + settings.getLogTag());
       }
 
-      String appStoragePath = PathUtils.getFilesDir(applicationContext);
-      String engineCachesPath = PathUtils.getCacheDirectory(applicationContext);
       long initTimeMillis = SystemClock.uptimeMillis() - initStartTimestampMillis;
       FlutterJNI.nativeInit(
           applicationContext,
           shellArgs.toArray(new String[0]),
           kernelPath,
-          appStoragePath,
-          engineCachesPath,
+          result.appStoragePath,
+          result.engineCachesPath,
           initTimeMillis);
 
       initialized = true;
@@ -235,8 +270,15 @@ public void ensureInitializationCompleteAsync(
             new Runnable() {
               @Override
               public void run() {
-                if (resourceExtractor != null) {
-                  resourceExtractor.waitForCompletion();
+                InitResult result;
+                try {
+                  result = initResultFuture.get();
+                } catch (Exception e) {
+                  Log.e(TAG, "Flutter initialization failed.", e);
+                  throw new RuntimeException(e);
+                }
+                if (result.resourceExtractor != null) {
+                  result.resourceExtractor.waitForCompletion();
                 }
                 new Handler(Looper.getMainLooper())
                     .post(
@@ -288,7 +330,8 @@ private void initConfig(@NonNull Context applicationContext) {
   }
 
   /** Extract assets out of the APK that need to be cached as uncompressed files on disk. */
-  private void initResources(@NonNull Context applicationContext) {
+  private ResourceExtractor initResources(@NonNull Context applicationContext) {
+    ResourceExtractor resourceExtractor = null;
     if (BuildConfig.DEBUG || BuildConfig.JIT_RELEASE) {
       final String dataDirPath = PathUtils.getDataDirectory(applicationContext);
       final String packageName = applicationContext.getPackageName();
@@ -306,6 +349,7 @@ private void initResources(@NonNull Context applicationContext) {
 
       resourceExtractor.start();
     }
+    return resourceExtractor;
   }
 
   @NonNull

testing/scenario_app/android/app/src/main/AndroidManifest.xml

@@ -3,7 +3,7 @@
     package="dev.flutter.scenarios">
 
     <application
-        android:name="io.flutter.app.FlutterApplication"
+        android:name=".ScenarioApplication"
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"

testing/scenario_app/android/app/src/main/java/dev/flutter/scenarios/ScenarioApplication.java

@@ -0,0 +1,21 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package dev.flutter.scenarios;
+
+import android.os.StrictMode;
+import io.flutter.app.FlutterApplication;
+
+public class ScenarioApplication extends FlutterApplication {
+  @Override
+  public void onCreate() {
+    StrictMode.setThreadPolicy(
+        new StrictMode.ThreadPolicy.Builder()
+            .detectDiskReads()
+            .detectDiskWrites()
+            .penaltyDeath()
+            .build());
+    super.onCreate();
+  }
+}