ListenableFutureTask.java

/**
 * Copyright (C) 2014 Open Whisper Systems
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.thoughtcrime.securesms.util;

import android.support.annotation.Nullable;

import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.FutureTask;

public class ListenableFutureTask<V> extends FutureTask<V> {

  private final List<FutureTaskListener<V>> listeners = new LinkedList<>();

  @Nullable
  private final Object identifier;

  @Nullable
  private final Executor callbackExecutor;

  public ListenableFutureTask(Callable<V> callable) {
    this(callable, null);
  }

  public ListenableFutureTask(Callable<V> callable, @Nullable Object identifier) {
    this(callable, identifier, null);
  }

  public ListenableFutureTask(Callable<V> callable, @Nullable Object identifier, @Nullable Executor callbackExecutor) {
    super(callable);
    this.identifier       = identifier;
    this.callbackExecutor = callbackExecutor;
  }


  public ListenableFutureTask(final V result) {
    this(result, null);
  }

  public ListenableFutureTask(final V result, @Nullable Object identifier) {
    super(new Callable<V>() {
      @Override
      public V call() throws Exception {
        return result;
      }
    });
    this.identifier       = identifier;
    this.callbackExecutor = null;
    this.run();
  }

  public synchronized void addListener(FutureTaskListener<V> listener) {
    if (this.isDone()) {
      callback(listener);
    } else {
      this.listeners.add(listener);
    }
  }

  public synchronized void removeListener(FutureTaskListener<V> listener) {
    this.listeners.remove(listener);
  }

  @Override
  protected synchronized void done() {
    callback();
  }

  private void callback() {
    Runnable callbackRunnable = new Runnable() {
      @Override
      public void run() {
        for (FutureTaskListener<V> listener : listeners) {
          callback(listener);
        }
      }
    };

    if (callbackExecutor == null) callbackRunnable.run();
    else                          callbackExecutor.execute(callbackRunnable);
  }

  private void callback(FutureTaskListener<V> listener) {
    if (listener != null) {
      try {
        listener.onSuccess(get());
      } catch (InterruptedException e) {
        throw new AssertionError(e);
      } catch (ExecutionException e) {
        listener.onFailure(e);
      }
    }
  }

  @Override
  public boolean equals(Object other) {
    if (other != null && other instanceof ListenableFutureTask && this.identifier != null) {
      return identifier.equals(other);
    } else {
      return super.equals(other);
    }
  }

  @Override
  public int hashCode() {
    if (identifier != null) return identifier.hashCode();
    else                    return super.hashCode();
  }
}