| 1 | package com.hammurapi.common; |
| 2 | |
| 3 | import java.lang.ref.Reference; |
| 4 | import java.lang.ref.ReferenceQueue; |
| 5 | import java.lang.ref.WeakReference; |
| 6 | import java.util.ArrayList; |
| 7 | import java.util.Iterator; |
| 8 | import java.util.LinkedList; |
| 9 | import java.util.List; |
| 10 | |
| 11 | /** |
| 12 | * Maintains weak references to objects. Removes cleared entries in |
| 13 | * getIdentity() method. |
| 14 | * @author Pavel Vlasov |
| 15 | * |
| 16 | */ |
| 17 | public class WeakIdentityManager implements IdentityManager<Object> { |
| 18 | |
| 19 | private static ReferenceQueue<Object> rq = new ReferenceQueue<Object>(); |
| 20 | |
| 21 | private static long[] counter = {0}; |
| 22 | |
| 23 | private static class Entry extends WeakReference<Object> { |
| 24 | String identity; |
| 25 | |
| 26 | Entry(Object obj) { |
| 27 | super(obj, rq); |
| 28 | identity="wim_"+Long.toString(counter[0]++, Character.MAX_RADIX); |
| 29 | } |
| 30 | } |
| 31 | |
| 32 | private static List<IdentityExtractor<?>> extractors = new ArrayList<IdentityExtractor<?>>(); |
| 33 | |
| 34 | static { |
| 35 | Thread reaper = new Thread("Removes cleared references") { |
| 36 | |
| 37 | @Override |
| 38 | public void run() { |
| 39 | while (true) { |
| 40 | try { |
| 41 | Reference<? extends Object> removed = rq.remove(); |
| 42 | if (removed instanceof Entry) { |
| 43 | synchronized (counter) { |
| 44 | Iterator<Entry> it = entries.iterator(); |
| 45 | while (it.hasNext()) { |
| 46 | Entry entry = it.next(); |
| 47 | if (removed==entry) { |
| 48 | it.remove(); |
| 49 | break; |
| 50 | } |
| 51 | } |
| 52 | } |
| 53 | } |
| 54 | } catch (InterruptedException e) { |
| 55 | return; // Time to exit. |
| 56 | } |
| 57 | } |
| 58 | } |
| 59 | }; |
| 60 | |
| 61 | reaper.setDaemon(true); |
| 62 | reaper.start(); |
| 63 | } |
| 64 | |
| 65 | private static LinkedList<Entry> entries = new LinkedList<Entry>(); |
| 66 | |
| 67 | @SuppressWarnings("unchecked") |
| 68 | public Object getIdentity(Object obj) { |
| 69 | if (obj==null) { |
| 70 | return null; |
| 71 | } |
| 72 | if (obj instanceof Identifiable) { |
| 73 | return ((Identifiable<Object>) obj).getIdentity(); |
| 74 | } |
| 75 | for (IdentityExtractor<?> ie: extractors) { |
| 76 | Object identity = ie.getIdentity(obj); |
| 77 | if (identity!=null) { |
| 78 | return identity; |
| 79 | } |
| 80 | } |
| 81 | synchronized (counter) { |
| 82 | Iterator<Entry> it = entries.iterator(); |
| 83 | while (it.hasNext()) { |
| 84 | Entry entry = it.next(); |
| 85 | Object eObj = entry.get(); |
| 86 | if (eObj==null) { |
| 87 | it.remove(); |
| 88 | } else if (eObj==obj) { |
| 89 | return entry.identity; |
| 90 | } |
| 91 | } |
| 92 | Entry entry = new Entry(obj); |
| 93 | entries.add(entry); |
| 94 | return entry.identity; |
| 95 | } |
| 96 | } |
| 97 | |
| 98 | } |