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CreateReducersApi xref
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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.giraph.block_app.framework.api;
19  
20  import org.apache.giraph.block_app.framework.piece.global_comm.ReducerHandle;
21  import org.apache.giraph.reducers.ReduceOperation;
22  import org.apache.hadoop.io.Writable;
23  
24  /**
25   * Api for creating reducer handles.
26   */
27  public interface CreateReducersApi extends BlockConfApi {
28  
29    /**
30     * Create local reducer, returning a handle to it.
31     *
32     * Local reducer means that each worker thread has it's own local partially
33     * reduced value, which are at the end reduced all together.
34     * Preferable, unless it cannot be used, because all copies of the object
35     * do not fit the memory.
36     */
37    <S, R extends Writable> ReducerHandle<S, R> createLocalReducer(
38        ReduceOperation<S, R> reduceOp);
39  
40    /**
41     * Create local reducer, returning a handle to it.
42     *
43     * Local reducer means that each worker thread has it's own local partially
44     *  reduced value, which are at the end reduced all together.
45     * Preferable, unless it cannot be used, because all copies of the object
46     * do not fit the memory.
47     */
48    <S, R extends Writable> ReducerHandle<S, R> createLocalReducer(
49        ReduceOperation<S, R> reduceOp, R globalInitialValue);
50  
51    /**
52     * Create global reducer, returning a handle to it.
53     *
54     * Global reducer means that there is only one value for each worker,
55     * and each call to reduce will have to obtain a global lock, and incur
56     * synchronization costs.
57     * Use only when objects are so large, that having many copies cannot
58     * fit into memory.
59     */
60    <S, R extends Writable> ReducerHandle<S, R> createGlobalReducer(
61        ReduceOperation<S, R> reduceOp);
62  
63    /**
64     * Create global reducer, returning a handle to it.
65     *
66     * Global reducer means that there is only one value for each worker,
67     * and each call to reduce will have to obtain a global lock, and incur
68     * synchronization costs.
69     * Use only when objects are so large, that having many copies cannot
70     * fit into memory.
71     */
72    <S, R extends Writable> ReducerHandle<S, R> createGlobalReducer(
73        ReduceOperation<S, R> reduceOp, R globalInitialValue);
74  
75    /**
76     * Function that creates a reducer - abstracting away whether it is
77     * local or global reducer
78     */
79    public interface CreateReducerFunctionApi {
80      <S, R extends Writable> ReducerHandle<S, R> createReducer(
81          ReduceOperation<S, R> reduceOp);
82    }
83  }