hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/retry/CallReturn.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.hadoop.io.retry;

import com.google.common.base.Preconditions;

/** The call return from a method invocation. */
class CallReturn {
  /** The return state. */
  enum State {
    /** Call is returned successfully. */
    RETURNED,
    /** Call throws an exception. */
    EXCEPTION,
    /** Call should be retried according to the {@link RetryPolicy}. */
    RETRY,
    /** Call, which is async, is still in progress. */
    ASYNC_CALL_IN_PROGRESS,
    /** Call, which is async, just has been invoked. */
    ASYNC_INVOKED
  }

  static final CallReturn ASYNC_CALL_IN_PROGRESS = new CallReturn(
      State.ASYNC_CALL_IN_PROGRESS);
  static final CallReturn ASYNC_INVOKED = new CallReturn(State.ASYNC_INVOKED);
  static final CallReturn RETRY = new CallReturn(State.RETRY);

  private final Object returnValue;
  private final Throwable thrown;
  private final State state;

  CallReturn(Object r) {
    this(r, null, State.RETURNED);
  }
  CallReturn(Throwable t) {
    this(null, t, State.EXCEPTION);
    Preconditions.checkNotNull(t);
  }
  private CallReturn(State s) {
    this(null, null, s);
  }
  private CallReturn(Object r, Throwable t, State s) {
    Preconditions.checkArgument(r == null || t == null);
    returnValue = r;
    thrown = t;
    state = s;
  }

  State getState() {
    return state;
  }

  Object getReturnValue() throws Throwable {
    if (state == State.EXCEPTION) {
      throw thrown;
    }
    Preconditions.checkState(state == State.RETURNED, "state == %s", state);
    return returnValue;
  }
}