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    
021    package cascading.scheme;
022    
023    import 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     */
034    public 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      }