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comparison src/goodjava/util/MapReduce.java @ 2171:8b77bd42864d

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add add Thread.map_reduce
author Franklin Schmidt <fschmidt@gmail.com>
date Sun, 22 Mar 2026 19:24:52 -0600
parents
children 75c45f1a743e
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2170:a59d0bf68830 2171:8b77bd42864d
1 package goodjava.util;
2
3 import java.util.Collections;
4 import java.util.List;
5 import java.util.ArrayList;
6 import java.util.Map;
7 import java.util.HashMap;
8 import java.util.WeakHashMap;
9 import java.util.Set;
10
11
12 public class MapReduce {
13
14 public interface Mapper {
15 public List map(Object arg);
16 }
17
18 public interface Handler extends Mapper {
19 public List reduce(List<List> lists);
20 }
21
22 private static Map<String,MapReduce> instances = new HashMap<String,MapReduce>();
23
24 // an active handler will be arbitrarily chosen for reduce
25 public static synchronized MapReduce register(String key,Mapper mapper) {
26 MapReduce mr = instances.get(key);
27 if( mr == null ) {
28 mr = new MapReduce();
29 instances.put(key,mr);
30 }
31 mr.mappers.add(mapper);
32 return mr;
33 }
34
35 private Set<Mapper> mappers = Collections.newSetFromMap(new WeakHashMap<Mapper, Boolean>());
36
37 public List run(Object arg) {
38 List<List> lists = new ArrayList<List>();
39 Handler lastHandler = null;
40 Mapper[] snapshot = mappers.toArray(new Mapper[0]);
41 for( Mapper m : snapshot ) {
42 lists.add( m.map(arg) );
43 if( m instanceof Handler )
44 lastHandler = (Handler)m;
45 }
46 return lastHandler==null ? Collections.emptyList() : lastHandler.reduce(lists);
47 }
48 }