content: /*
   * Copyright (C) 2017 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.adaway.util;
  
  import android.os.Handler;
  import android.os.Looper;
  
  import androidx.annotation.NonNull;
  
  import java.util.concurrent.Executor;
  import java.util.concurrent.Executors;
  
  /**
   * Global executor pools for the whole application.
   * <p>
   * Grouping tasks like this avoids the effects of task starvation (e.g. disk reads don't wait behind
   * webservice requests).
   * Source: https://github.com/googlecodelabs/android-build-an-app-architecture-components/blob/7364e9013419952b00aa582553aa1466c1a1dede/app/src/main/java/com/example/android/sunshine/AppExecutors.java
   */
  public class AppExecutors {
  
      // For Singleton instantiation
      private static final Object LOCK = new Object();
      private static AppExecutors sInstance;
      private final Executor diskIO;
      private final Executor mainThread;
      private final Executor networkIO;
  
      private AppExecutors(Executor diskIO, Executor networkIO, Executor mainThread) {
          this.diskIO = diskIO;
          this.networkIO = networkIO;
          this.mainThread = mainThread;
      }
  
      public static AppExecutors getInstance() {
          if (sInstance == null) {
              synchronized (LOCK) {
                  sInstance = new AppExecutors(
                          Executors.newSingleThreadExecutor(),
                          Executors.newFixedThreadPool(3),
                          new MainThreadExecutor()
                  );
              }
          }
          return sInstance;
      }
  
      public Executor diskIO() {
          return diskIO;
      }
  
      public Executor networkIO() {
          return networkIO;
      }
  
      public Executor mainThread() {
          return mainThread;
      }
  
      private static class MainThreadExecutor implements Executor {
          private Handler mainThreadHandler = new Handler(Looper.getMainLooper());
  
          @Override
          public void execute(@NonNull Runnable command) {
              mainThreadHandler.post(command);
          }
      }
  }