Synchronize write to two collections
- by glaz666
I need to put some value to maps if it is not there yet. The key-value (if set) should always be in two collections (that is put should happen in two maps atomically). I have tried to implement this as follows:
private final ConcurrentMap<String, Object> map1 = new ConcurrentHashMap<String, Object>();
private final ConcurrentMap<String, Object> map2 = new ConcurrentHashMap<String, Object>();
public Object putIfAbsent(String key) {
Object retval = map1.get(key);
if (retval == null) {
synchronized (map1) {
retval = map1.get(key);
if (retval == null) {
Object value = new Object(); //or get it somewhere
synchronized (map2) {
map1.put(key, value);
map2.put(key, new Object());
}
retval = value;
}
}
}
return retval;
}
public void doSomething(String key) {
Object obj1 = map1.get(key);
Object obj2 = map2.get(key);
//do smth
}
Will that work fine in all cases? Thanks
