lottie/src/main/java/com/airbnb/lottie/LottieTask.java

package com.airbnb.lottie;

import android.os.Handler;
import android.os.Looper;
import androidx.annotation.Nullable;
import androidx.annotation.RestrictTo;

import com.airbnb.lottie.utils.Logger;

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;

/**
 * Helper to run asynchronous tasks with a result.
 * Results can be obtained with {@link #addListener(LottieListener)}.
 * Failures can be obtained with {@link #addFailureListener(LottieListener)}.
 *
 * A task will produce a single result or a single failure.
 */
public class LottieTask<T> {

  /**
   * Set this to change the executor that LottieTasks are run on. This will be the executor that composition parsing and url
   * fetching happens on.
   *
   * You may change this to run deserialization synchronously for testing.
   */
  @SuppressWarnings("WeakerAccess")
  public static Executor EXECUTOR = Executors.newCachedThreadPool();

  /* Preserve add order. */
  private final Set<LottieListener<T>> successListeners = new LinkedHashSet<>(1);
  private final Set<LottieListener<Throwable>> failureListeners = new LinkedHashSet<>(1);
  private final Handler handler = new Handler(Looper.getMainLooper());

  @Nullable private volatile LottieResult<T> result = null;

  @RestrictTo(RestrictTo.Scope.LIBRARY)
  public LottieTask(Callable<LottieResult<T>> runnable) {
    this(runnable, false);
  }

  /**
   * runNow is only used for testing.
   */
  @RestrictTo(RestrictTo.Scope.LIBRARY)
  LottieTask(Callable<LottieResult<T>> runnable, boolean runNow) {
    if (runNow) {
      try {
        setResult(runnable.call());
      } catch (Throwable e) {
        setResult(new LottieResult<T>(e));
      }
    } else {
      EXECUTOR.execute(new LottieFutureTask(runnable));
    }
  }

  private void setResult(@Nullable LottieResult<T> result) {
    if (this.result != null) {
      throw new IllegalStateException("A task may only be set once.");
    }
    this.result = result;
    notifyListeners();
  }

  /**
   * Add a task listener. If the task has completed, the listener will be called synchronously.
   * @return the task for call chaining.
   */
  public synchronized LottieTask<T> addListener(LottieListener<T> listener) {
    if (result != null && result.getValue() != null) {
      listener.onResult(result.getValue());
    }

    successListeners.add(listener);
    return this;
  }

  /**
   * Remove a given task listener. The task will continue to execute so you can re-add
   * a listener if neccesary.
   * @return the task for call chaining.
   */
  public synchronized LottieTask<T> removeListener(LottieListener<T> listener) {
    successListeners.remove(listener);
    return this;
  }

  /**
   * Add a task failure listener. This will only be called in the even that an exception
   * occurs. If an exception has already occurred, the listener will be called immediately.
   * @return the task for call chaining.
   */
  public synchronized LottieTask<T> addFailureListener(LottieListener<Throwable> listener) {
    if (result != null && result.getException() != null) {
      listener.onResult(result.getException());
    }

    failureListeners.add(listener);
    return this;
  }

  /**
   * Remove a given task failure listener. The task will continue to execute so you can re-add
   * a listener if neccesary.
   * @return the task for call chaining.
   */
  public synchronized LottieTask<T> removeFailureListener(LottieListener<Throwable> listener) {
    failureListeners.remove(listener);
    return this;
  }

  private void notifyListeners() {
    // Listeners should be called on the main thread.
    handler.post(new Runnable() {
      @Override public void run() {
        if (result == null) {
          return;
        }
        // Local reference in case it gets set on a background thread.
        LottieResult<T> result = LottieTask.this.result;
        if (result.getValue() != null) {
          notifySuccessListeners(result.getValue());
        } else {
          notifyFailureListeners(result.getException());
        }
      }
    });
  }

  private synchronized void notifySuccessListeners(T value) {
    // Allows listeners to remove themselves in onResult.
    // Otherwise we risk ConcurrentModificationException.
    List<LottieListener<T>> listenersCopy = new ArrayList<>(successListeners);
    for (LottieListener<T> l : listenersCopy) {
      l.onResult(value);
    }
  }

  private synchronized void notifyFailureListeners(Throwable e) {
    // Allows listeners to remove themselves in onResult.
    // Otherwise we risk ConcurrentModificationException.
    List<LottieListener<Throwable>> listenersCopy = new ArrayList<>(failureListeners);
    if (listenersCopy.isEmpty()) {
      Logger.warning("Lottie encountered an error but no failure listener was added:", e);
      return;
    }

    for (LottieListener<Throwable> l : listenersCopy) {
      l.onResult(e);
    }
  }

  private class LottieFutureTask extends FutureTask<LottieResult<T>> {
    LottieFutureTask(Callable<LottieResult<T>> callable) {
      super(callable);
    }

    @Override
    protected void done() {
      if (isCancelled()) {
        // We don't need to notify and listeners if the task is cancelled.
        return;
      }

      try {
        setResult(get());
      } catch (InterruptedException | ExecutionException e) {
        setResult(new LottieResult<T>(e));
      }
    }
  }
}