001/*
002 * Copyright (c) 2007-2015 Concurrent, Inc. All Rights Reserved.
003 *
004 * Project and contact information: http://www.cascading.org/
005 *
006 * This file is part of the Cascading project.
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *     http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020
021package cascading.scheme;
022
023import cascading.tuple.TupleEntry;
024
025/**
026 * SourceCall provides access to the current {@link Scheme#source(cascading.flow.FlowProcess, SourceCall)} invocation
027 * arguments.
028 * <p/>
029 * Use the Context to store thread local values.
030 *
031 * @param <Context>
032 * @param <Input>
033 */
034public interface SourceCall<Context, Input>
035  {
036  /**
037   * Method getContext returns the context of this SourceCall object.
038   *
039   * @return the context (type C) of this SourceCall object.
040   */
041  Context getContext();
042
043  /**
044   * Method setContext sets the context of this SourceCall object.
045   *
046   * @param context the context of this SourceCall object.
047   */
048  void setContext( Context context );
049
050  /**
051   * Method getIncomingEntry returns a pre-prepared {@link TupleEntry} to be populated
052   * with the input values from {@link #getInput()}.
053   * <p/>
054   * That is, using the getInput() method, retrieve the current incoming values and
055   * place them into the getIncomingEntry() via {@link TupleEntry#setTuple(cascading.tuple.Tuple)}
056   * or by modifying the tuple returned from {@link cascading.tuple.TupleEntry#getTuple()}.
057   * <p/>
058   * The returned Tuple entry is guaranteed to be the size of the declared incoming source fields.
059   * <p/>
060   * The returned TupleEntry from this method is modifiable and is intended to be re-used. This is an exception to
061   * the general rule that passed TupleEntry instances must not be modified.
062   *
063   * @return TupleEntry
064   */
065  TupleEntry getIncomingEntry();
066
067  /**
068   * Method getInput returns the input mechanism for the underlying platform used to retrieve new values (records,
069   * lines, etc).
070   * <p/>
071   * Do not cache the returned value as it may change.
072   *
073   * @return the platform dependent input handler
074   */
075  Input getInput();
076  }