/// <inheritdoc/>
public override TValue GetOrCreate(TKey key, Func <TKey, TValue> valueFactory)
{
object mapValue = map.GetOrAdd(key, (k) =>
{
// We had never cached an instance for this key.
if (valueFactory is null)
{
return(CacheValue <TValue> .GetInstance(null));
}
return(valueFactory(k) ?? (object)CacheValue <TValue> .GetInstance(null));
});
if (!(mapValue is CacheValue <TValue> cv))
{
// The value was stored directly.
return((TValue)mapValue);
}
if (cv.IsNull)
{
return(null);
}
return(cv.Get());
}
public override V GetInstance(K key, D data)
{
// We synchronize twice, once in the ConcurrentHashMap and
// once in valueRef.resetIfCleared(value),
// because we prefer the fine-granularity locking of the ConcurrentHashMap
// over coarser locking on the whole cache instance.
// We use a CacheValue (a second level of indirection) because
// ConcurrentHashMap.putIfAbsent() never replaces the key's value, and if it were
// a simple Reference we would not be able to reset its value after it has been cleared.
// (And ConcurrentHashMap.put() always replaces the value, which we don't want either.)
object mapValue = null;
lock (map)
map.TryGetValue(key, out mapValue);
if (mapValue != null)
{
if (!(mapValue is CacheValue <V>))
{
// The value was stored directly.
return((V)mapValue);
}
CacheValue <V> cv = (CacheValue <V>)mapValue;
if (cv.IsNull)
{
return(null);
}
V value = cv.Get();
if (value != null)
{
return(value);
}
// The instance has been evicted, its Reference cleared.
// Create and set a new instance.
value = CreateInstance(key, data);
return(cv.ResetIfCleared(value));
}
else /* valueRef == null */
{
// We had never cached an instance for this key.
V value = CreateInstance(key, data);
mapValue = (value != null && CacheValue <V> .FutureInstancesWillBeStrong) ?
value : (object)CacheValue <V> .GetInstance(value);
object temp;
lock (map)
{
// ICU4N TODO: use PutIfAbsent logic from elsewhere to utilize ConcurrentDictionary...?
if (!map.TryGetValue(key, out temp))
{
// put if absent
map[key] = mapValue;
}
mapValue = temp;
}
if (mapValue == null)
{
// Normal "put": Our new value is now cached.
return(value);
}
// Race condition: Another thread beat us to putting a CacheValue
// into the map. Return its value, but just in case the garbage collector
// was aggressive, we also offer our new instance for caching.
if (!(mapValue is CacheValue <V>))
{
// The value was stored directly.
return((V)mapValue);
}
CacheValue <V> cv = (CacheValue <V>)mapValue;
return(cv.ResetIfCleared(value));
}
}
