content: /*
   * 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.beam.runners.dataflow.worker.util.common.worker;
  
  /**
   * The abstract base class for Operations, which correspond to Instructions in the original MapTask
   * InstructionGraph.
   *
   * <p>Call start() to start the operation.
   *
   * <p>A read operation's start() method actually reads the data, and in effect runs the pipeline.
   *
   * <p>Call finish() to finish the operation.
   *
   * <p>Call abort() if the Operation's execution needs to be aborted, e.g., because an exception is
   * thrown during any of the above, to do clean up that might be done as part of finish() in a
   * successful execution.
   *
   * <p>Since both start() and finish() may call process() on this operation's consumers, start an
   * operation after starting its consumers, and finish an operation before finishing its consumers.
   * Operations can be abort()ed in any order.
   */
  public abstract class Operation {
  
    protected final OperationContext context;
  
    /**
     * The array of consuming receivers, one per operation output "port" (e.g., DoFn main or side
     * output). A receiver might be null if that output isn't being consumed.
     */
    public final OutputReceiver[] receivers;
  
    /** The possible initialization states of an Operation. For internal self-checking purposes. */
    public enum InitializationState {
      // start() hasn't yet been called.
      UNSTARTED,
  
      // start() has been called, but finish() hasn't yet been called.
      STARTED,
  
      // finish() has been called.
      FINISHED,
  
      // abort() has been called.
      ABORTED,
    }
  
    /**
     * The initialization state of this Operation.
     *
     * <p>Written from one thread, but can be read by concurrent threads.
     */
    public InitializationState initializationState = InitializationState.UNSTARTED;
  
    /**
     * The lock protecting the initialization state.
     *
     * <p>Subclasses can use this lock to protect their own state. However, this lock should be held
     * only for short, bounded amounts of time.
     */
    protected final Object initializationStateLock = new Object();
  
    public Operation(OutputReceiver[] receivers, OperationContext context) {
      this.receivers = receivers;
      this.context = context;
    }
  
    /** Checks that this operation is not yet started, throwing an exception otherwise. */
    void checkUnstarted() {
      if (!(initializationState == InitializationState.UNSTARTED
          || (initializationState == InitializationState.FINISHED && supportsRestart()))) {
        throw new AssertionError("expecting this instruction to not yet be started");
      }
    }
  
    /**
     * Checks that this operation has been started but not yet finished, throwing an exception
     * otherwise.
     */
    void checkStarted() {
      if (initializationState != InitializationState.STARTED) {
        throw new AssertionError("expecting this instruction to be started");
      }
    }
  
    /** Checks that this operation has been finished, throwing an exception otherwise. */
    void checkFinished() {
      if (initializationState != InitializationState.FINISHED) {
        throw new AssertionError("expecting this instruction to be finished");
      }
    }
  
    /** Returns true if this Operation has been finished. */
    boolean isFinished() {
      return (initializationState == InitializationState.FINISHED);
    }
  
    /** Returns true if this Operation has been aborted. */
    boolean isAborted() {
      return (initializationState == InitializationState.ABORTED);
    }
  
    /**
     * Starts this Operation's execution. Called after all successsor consuming operations have been
     * started.
     */
    public void start() throws Exception {
      synchronized (initializationStateLock) {
        checkUnstarted();
        initializationState = InitializationState.STARTED;
      }
    }
  
    /**
     * Finishes this Operation's execution. Called after all predecessor producing operations have
     * been finished.
     */
    public void finish() throws Exception {
      synchronized (initializationStateLock) {
        checkStarted();
        initializationState = InitializationState.FINISHED;
      }
    }
  
    /** Aborts this Operation's execution. */
    public void abort() throws Exception {
      synchronized (initializationStateLock) {
        initializationState = InitializationState.ABORTED;
      }
    }
  
    /** Returns true if this Operation can be started again after it is finished. */
    public boolean supportsRestart() {
      return false;
    }
  
    public OperationContext getContext() {
      return context;
    }
  }
  