ThreadPoolExecutorExtractor.java

package com.google.android.apps.common.testing.ui.espresso.base;

import com.google.common.base.Optional;

import android.os.Build;
import android.os.Handler;
import android.os.Looper;

import java.lang.reflect.Field;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import java.util.concurrent.ThreadPoolExecutor;

import javax.inject.Inject;
import javax.inject.Singleton;

/**
 * Extracts ThreadPoolExecutors used by pieces of android.
 *
 * We do some work to ensure that we load the classes containing these thread pools
 * on the main thread, since they may have static initialization that assumes access
 * to the main looper.
 */
@Singleton
final class ThreadPoolExecutorExtractor {
  private static final String ASYNC_TASK_CLASS_NAME = "android.os.AsyncTask";
  private static final String MODERN_ASYNC_TASK_CLASS_NAME =
      "android.support.v4.content.ModernAsyncTask";
  private static final String MODERN_ASYNC_TASK_FIELD_NAME = "THREAD_POOL_EXECUTOR";
  private static final String LEGACY_ASYNC_TASK_FIELD_NAME = "sExecutor";
  private final Handler mainHandler;

  @Inject
  ThreadPoolExecutorExtractor(Looper looper) {
    mainHandler = new Handler(looper);
  }


  public ThreadPoolExecutor getAsyncTaskThreadPool() {
    FutureTask<Optional<ThreadPoolExecutor>> getTask = null;
    if (Build.VERSION.SDK_INT < 11) {
      getTask = new FutureTask<Optional<ThreadPoolExecutor>>(LEGACY_ASYNC_TASK_EXECUTOR);
    } else {
      getTask = new FutureTask<Optional<ThreadPoolExecutor>>(POST_HONEYCOMB_ASYNC_TASK_EXECUTOR);
    }

    try {
      return runOnMainThread(getTask).get().get();
    } catch (InterruptedException ie) {
      throw new RuntimeException("Interrupted while trying to get the async task executor!", ie);
    } catch (ExecutionException ee) {
      throw new RuntimeException(ee.getCause());
    }
  }

  public Optional<ThreadPoolExecutor> getCompatAsyncTaskThreadPool() {
    try {
      return runOnMainThread(
          new FutureTask<Optional<ThreadPoolExecutor>>(MODERN_ASYNC_TASK_EXTRACTOR)).get();
    } catch (InterruptedException ie) {
      throw new RuntimeException("Interrupted while trying to get the compat async executor!", ie);
    } catch (ExecutionException ee) {
      throw new RuntimeException(ee.getCause());
    }
  }

  private <T> FutureTask<T> runOnMainThread(final FutureTask<T> futureToRun) {
    if (Looper.myLooper() != Looper.getMainLooper()) {
      final CountDownLatch latch = new CountDownLatch(1);
      mainHandler.post(new Runnable() {
        @Override
        public void run() {
          try {
            futureToRun.run();
          } finally {
            latch.countDown();
          }
        }
      });
      try {
        latch.await();
      } catch (InterruptedException ie) {
        if (!futureToRun.isDone()) {
          throw new RuntimeException("Interrupted while waiting for task to complete.");
        }
      }
    } else {
      futureToRun.run();
    }

    return futureToRun;
  }

  private static final Callable<Optional<ThreadPoolExecutor>> MODERN_ASYNC_TASK_EXTRACTOR =
      new Callable<Optional<ThreadPoolExecutor>>() {
        @Override
        public Optional<ThreadPoolExecutor> call() throws Exception {
          try {
            Class<?> modernClazz = Class.forName(MODERN_ASYNC_TASK_CLASS_NAME);
            Field executorField = modernClazz.getField(MODERN_ASYNC_TASK_FIELD_NAME);
            return Optional.of((ThreadPoolExecutor) executorField.get(null));
          } catch (ClassNotFoundException cnfe) {
            return Optional.<ThreadPoolExecutor>absent();
          }
        }
      };

  private static final Callable<Class<?>> LOAD_ASYNC_TASK_CLASS =
      new Callable<Class<?>>() {
        @Override
        public Class<?> call() throws Exception {
          return Class.forName(ASYNC_TASK_CLASS_NAME);
        }
      };

  private static final Callable<Optional<ThreadPoolExecutor>> LEGACY_ASYNC_TASK_EXECUTOR =
      new Callable<Optional<ThreadPoolExecutor>>() {
        @Override
        public Optional<ThreadPoolExecutor> call() throws Exception {
          Field executorField = LOAD_ASYNC_TASK_CLASS.call()
              .getDeclaredField(LEGACY_ASYNC_TASK_FIELD_NAME);
          executorField.setAccessible(true);
          return Optional.of((ThreadPoolExecutor) executorField.get(null));
        }
      };

  private static final Callable<Optional<ThreadPoolExecutor>> POST_HONEYCOMB_ASYNC_TASK_EXECUTOR =
      new Callable<Optional<ThreadPoolExecutor>>() {
        @Override
        public Optional<ThreadPoolExecutor> call() throws Exception {
          Field executorField = LOAD_ASYNC_TASK_CLASS.call()
              .getField(MODERN_ASYNC_TASK_FIELD_NAME);
          return Optional.of((ThreadPoolExecutor) executorField.get(null));
        }
      };
}