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MapReduce cleanup
author Franklin Schmidt <fschmidt@gmail.com>
date Sun, 22 Mar 2026 20:58:17 -0600
parents 8b77bd42864d
children
comparison
equal deleted inserted replaced
2171:8b77bd42864d 2172:75c45f1a743e
9 import java.util.Set; 9 import java.util.Set;
10 10
11 11
12 public class MapReduce { 12 public class MapReduce {
13 13
14 public interface Mapper { 14 public interface Handler {
15 public List map(Object arg); 15 public List map(Object arg);
16 }
17
18 public interface Handler extends Mapper {
19 public List reduce(List<List> lists); 16 public List reduce(List<List> lists);
20 } 17 }
21 18
22 private static Map<String,MapReduce> instances = new HashMap<String,MapReduce>(); 19 private static Map<String,MapReduce> instances = new HashMap<String,MapReduce>();
23 20
24 // an active handler will be arbitrarily chosen for reduce 21 // an active handler will be arbitrarily chosen for reduce
25 public static synchronized MapReduce register(String key,Mapper mapper) { 22 public static synchronized MapReduce register(String key,Handler handler) {
26 MapReduce mr = instances.get(key); 23 MapReduce mr = instances.get(key);
27 if( mr == null ) { 24 if( mr == null ) {
28 mr = new MapReduce(); 25 mr = new MapReduce();
29 instances.put(key,mr); 26 instances.put(key,mr);
30 } 27 }
31 mr.mappers.add(mapper); 28 mr.handlers.add(handler);
32 return mr; 29 return mr;
33 } 30 }
34 31
35 private Set<Mapper> mappers = Collections.newSetFromMap(new WeakHashMap<Mapper, Boolean>()); 32 private Set<Handler> handlers = Collections.newSetFromMap(new WeakHashMap<Handler, Boolean>());
36 33
37 public List run(Object arg) { 34 public List run(Object arg) {
38 List<List> lists = new ArrayList<List>(); 35 List<List> lists = new ArrayList<List>();
39 Handler lastHandler = null; 36 Handler lastHandler = null;
40 Mapper[] snapshot = mappers.toArray(new Mapper[0]); 37 Handler[] snapshot = handlers.toArray(new Handler[0]);
41 for( Mapper m : snapshot ) { 38 for( Handler h : snapshot ) {
42 lists.add( m.map(arg) ); 39 lists.add( h.map(arg) );
43 if( m instanceof Handler ) 40 lastHandler = h;
44 lastHandler = (Handler)m;
45 } 41 }
46 return lastHandler==null ? Collections.emptyList() : lastHandler.reduce(lists); 42 return lastHandler==null ? Collections.emptyList() : lastHandler.reduce(lists);
47 } 43 }
48 } 44 }