CallFuture.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.avro.ipc;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * A Future implementation for RPCs.
 */
public class CallFuture<T> implements Future<T>, Callback<T> {
  private final CountDownLatch latch = new CountDownLatch(1);
  private final Callback<T> chainedCallback;
  private T result = null;
  private Throwable error = null;

  /**
   * Creates a CallFuture.
   */
  public CallFuture() {
    this(null);
  }

  /**
   * Creates a CallFuture with a chained Callback which will be invoked
   * when this CallFuture's Callback methods are invoked.
   * @param chainedCallback the chained Callback to set.
   */
  public CallFuture(Callback<T> chainedCallback) {
    this.chainedCallback = chainedCallback;
  }

  /**
   * Sets the RPC response, and unblocks all threads waiting on {@link #get()}
   * or {@link #get(long, TimeUnit)}.
   * @param result the RPC result to set.
   */
  @Override
  public void handleResult(T result) {
    this.result = result;
    latch.countDown();
    if (chainedCallback != null) {
      chainedCallback.handleResult(result);
    }
  }

  /**
   * Sets an error thrown during RPC execution, and unblocks all threads waiting
   * on {@link #get()} or {@link #get(long, TimeUnit)}.
   * @param error the RPC error to set.
   */
  @Override
  public void handleError(Throwable error) {
    this.error = error;
    latch.countDown();
    if (chainedCallback != null) {
      chainedCallback.handleError(error);
    }
  }

  /**
   * Gets the value of the RPC result without blocking.
   * Using {@link #get()} or {@link #get(long, TimeUnit)} is usually
   * preferred because these methods block until the result is available or
   * an error occurs.
   * @return the value of the response, or null if no result was returned or
   * the RPC has not yet completed.
   */
  public T getResult() {
    return result;
  }

  /**
   * Gets the error that was thrown during RPC execution.  Does not block.
   * Either {@link #get()} or {@link #get(long, TimeUnit)} should be called
   * first because these methods block until the RPC has completed.
   * @return the RPC error that was thrown, or null if no error has occurred or
   * if the RPC has not yet completed.
   */
  public Throwable getError() {
    return error;
  }

  @Override
  public boolean cancel(boolean mayInterruptIfRunning) {
    return false;
  }

  @Override
  public boolean isCancelled() {
    return false;
  }

  @Override
  public T get() throws InterruptedException,
      ExecutionException {
    latch.await();
    if (error != null) {
      throw new ExecutionException(error);
    }
    return result;
  }

  @Override
  public T get(long timeout, TimeUnit unit)
      throws InterruptedException, ExecutionException, TimeoutException {
    if (latch.await(timeout, unit)) {
      if (error != null) {
        throw new ExecutionException(error);
      }
      return result;
    } else {
      throw new TimeoutException();
    }
  }

  /**
   * Waits for the CallFuture to complete without returning the result.
   * @throws InterruptedException if interrupted.
   */
  public void await() throws InterruptedException {
    latch.await();
  }

  /**
   * Waits for the CallFuture to complete without returning the result.
   * @param timeout the maximum time to wait.
   * @param unit the time unit of the timeout argument.
   * @throws InterruptedException if interrupted.
   * @throws TimeoutException if the wait timed out.
   */
  public void await(long timeout, TimeUnit unit)
    throws InterruptedException, TimeoutException {
    if (!latch.await(timeout, unit)) {
      throw new TimeoutException();
    }
  }

  @Override
  public boolean isDone() {
    return latch.getCount() <= 0;
  }
}