[path_provider_android] Move Path operations to background thread (flutter#3070)

Author: mehmetf

packages/path_provider/path_provider/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.6.19
+
+* Android implementation does path queries in the background thread rather than UI thread.
+
 ## 1.6.18
 
 * Keep handling deprecated Android v1 classes for backward compatibility.

packages/path_provider/path_provider/android/build.gradle

@@ -31,9 +31,16 @@ android {
     lintOptions {
         disable 'InvalidPackage'
     }
+    android {
+        compileOptions {
+            sourceCompatibility 1.8
+            targetCompatibility 1.8
+        }
+    }
 }
 
 dependencies {
     implementation 'androidx.annotation:annotation:1.1.0'
+    implementation 'com.google.guava:guava:20.0'
     testImplementation 'junit:junit:4.12'
 }

packages/path_provider/path_provider/android/src/main/java/io/flutter/plugins/pathprovider/PathProviderPlugin.java

@@ -7,7 +7,13 @@
 import android.content.Context;
 import android.os.Build.VERSION;
 import android.os.Build.VERSION_CODES;
+import android.os.Handler;
+import android.os.Looper;
 import androidx.annotation.NonNull;
+import com.google.common.util.concurrent.FutureCallback;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.SettableFuture;
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import io.flutter.embedding.engine.plugins.FlutterPlugin;
 import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
@@ -17,11 +23,21 @@
 import java.io.File;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.Callable;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
 
 public class PathProviderPlugin implements FlutterPlugin, MethodCallHandler {
 
   private Context context;
   private MethodChannel channel;
+  private final Executor uiThreadExecutor = new UiThreadExecutor();
+  private final Executor executor =
+      Executors.newSingleThreadExecutor(
+          new ThreadFactoryBuilder()
+              .setNameFormat("path-provider-background-%d")
+              .setPriority(Thread.NORM_PRIORITY)
+              .build());
 
   public PathProviderPlugin() {}
 
@@ -46,28 +62,52 @@ public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
     channel = null;
   }
 
+  private <T> void executeInBackground(Callable<T> task, Result result) {
+    final SettableFuture<T> future = SettableFuture.create();
+    Futures.addCallback(
+        future,
+        new FutureCallback<T>() {
+          public void onSuccess(T answer) {
+            result.success(answer);
+          }
+
+          public void onFailure(Throwable t) {
+            result.error(t.getClass().getName(), t.getMessage(), null);
+          }
+        },
+        uiThreadExecutor);
+    executor.execute(
+        () -> {
+          try {
+            future.set(task.call());
+          } catch (Throwable t) {
+            future.setException(t);
+          }
+        });
+  }
+
   @Override
   public void onMethodCall(MethodCall call, @NonNull Result result) {
     switch (call.method) {
       case "getTemporaryDirectory":
-        result.success(getPathProviderTemporaryDirectory());
+        executeInBackground(() -> getPathProviderTemporaryDirectory(), result);
         break;
       case "getApplicationDocumentsDirectory":
-        result.success(getPathProviderApplicationDocumentsDirectory());
+        executeInBackground(() -> getPathProviderApplicationDocumentsDirectory(), result);
         break;
       case "getStorageDirectory":
-        result.success(getPathProviderStorageDirectory());
+        executeInBackground(() -> getPathProviderStorageDirectory(), result);
         break;
       case "getExternalCacheDirectories":
-        result.success(getPathProviderExternalCacheDirectories());
+        executeInBackground(() -> getPathProviderExternalCacheDirectories(), result);
         break;
       case "getExternalStorageDirectories":
         final Integer type = call.argument("type");
         final String directoryName = StorageDirectoryMapper.androidType(type);
-        result.success(getPathProviderExternalStorageDirectories(directoryName));
+        executeInBackground(() -> getPathProviderExternalStorageDirectories(directoryName), result);
         break;
       case "getApplicationSupportDirectory":
-        result.success(getApplicationSupportDirectory());
+        executeInBackground(() -> getApplicationSupportDirectory(), result);
         break;
       default:
         result.notImplemented();
@@ -131,4 +171,13 @@ private List<String> getPathProviderExternalStorageDirectories(String type) {
 
     return paths;
   }
+
+  private static class UiThreadExecutor implements Executor {
+    private final Handler handler = new Handler(Looper.getMainLooper());
+
+    @Override
+    public void execute(Runnable command) {
+      handler.post(command);
+    }
+  }
 }

packages/path_provider/path_provider/pubspec.yaml

@@ -1,7 +1,7 @@
 name: path_provider
 description: Flutter plugin for getting commonly used locations on host platform file systems, such as the temp and app data directories.
 homepage: https://github.com/flutter/plugins/tree/master/packages/path_provider/path_provider
-version: 1.6.18
+version: 1.6.19
 
 flutter:
   plugin: