Mercurial Hosting > nabble

comparison src/cachingfilter/Locker.java @ 0:7ecd1a4ef557

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
add content
author Franklin Schmidt <fschmidt@gmail.com>
date Thu, 21 Mar 2019 19:15:52 -0600
parents
children
comparison
equal deleted inserted replaced
-1:000000000000 0:7ecd1a4ef557
1 package cachingfilter;
2
3 import java.util.Map;
4 import java.util.HashMap;
5 import java.util.concurrent.locks.Lock;
6 import java.util.concurrent.locks.ReentrantLock;
7
8
9 public final class Locker<T> {
10
11 private static class Tracker {
12 final ReentrantLock lock = new ReentrantLock();
13 int waiters = 0;
14 }
15
16 private final Map<T,Tracker> map = new HashMap<T,Tracker>();
17
18 public void lock(T obj) {
19 Tracker t;
20 synchronized(map) {
21 t = map.get(obj);
22 if( t == null ) {
23 t = new Tracker();
24 map.put(obj,t);
25 }
26 t.waiters++;
27 }
28 try {
29 t.lock.lock();
30 } finally {
31 synchronized(map) {
32 t.waiters--;
33 }
34 }
35 }
36
37 public boolean unlock(T obj) {
38 synchronized(map) {
39 Tracker t = map.get(obj);
40 if( t == null || !t.lock.isHeldByCurrentThread() )
41 return false;
42 t.lock.unlock();
43 if( t.waiters==0 ) {
44 map.remove(obj);
45 }
46 return true;
47 }
48 }
49
50 }