/**
* Utility method to clone a map, preserving immutable instances
*
* @param <K> the map key type, which must be {@link Serializable}
* @param <V> the map value type, which must be {@link Serializable}
* @param map the map to copy
* @param immutableClasses a set of classes that can be considered immutable over and above the
* {@link #DEFAULT_IMMUTABLE_CLASSES default set}
*/
public static <K extends Serializable, V extends Serializable> Map<K, V> cloneMap(
Map<K, V> map, Set<Class<?>> immutableClasses) {
Map<K, V> copy = new HashMap<K, V>((int) (map.size() * 1.3));
for (Map.Entry<K, V> element : map.entrySet()) {
K key = element.getKey();
V value = element.getValue();
// Clone as necessary
key = ValueProtectingMap.protectValue(key, immutableClasses);
value = ValueProtectingMap.protectValue(value, immutableClasses);
copy.put(key, value);
}
return copy;
}
/**
* Called by methods that need to force the map into a safe state.
*
* <p>This method can be called without any locks being active.
*/
private void cloneMap() {
readLock.lock();
try {
// Check that it hasn't been copied already
if (cloned) {
return;
}
} finally {
readLock.unlock();
}
/*
* Note: This space here is a window during which some code could have made
* a copy. Therefore we will do a cautious double-check.
*/
// Put in a write lock before cloning the map
writeLock.lock();
try {
// Check that it hasn't been copied already
if (cloned) {
return;
}
Map<K, V> copy = ValueProtectingMap.cloneMap(map, immutableClasses);
// Discard the original
this.map = copy;
this.cloned = true;
} finally {
writeLock.unlock();
}
}
@Override
public V get(Object key) {
readLock.lock();
try {
V value = map.get(key);
return ValueProtectingMap.protectValue(value, immutableClasses);
} finally {
readLock.unlock();
}
}