public override V Get() // serialize access
{
lock (this)
{
// re-check
Supplier <V> supplier = ValuesMap[SubKey];
if (supplier != this)
{
// something changed while we were waiting:
// might be that we were replaced by a CacheValue
// or were removed because of failure ->
// return null to signal WeakCache.get() to retry
// the loop
return(null);
}
// else still us (supplier == this)
// create new value
V value = null;
try
{
value = Objects.RequireNonNull(outerInstance.ValueFactory.Apply(Key, Parameter));
}
finally
{
if (value == null) // remove us on failure
{
ValuesMap.Remove(SubKey, this);
}
}
// the only path to reach here is with non-null value
Debug.Assert(value != null);
// wrap value with CacheValue (WeakReference)
CacheValue <V> cacheValue = new CacheValue <V>(value);
// try replacing us with CacheValue (this should always succeed)
if (ValuesMap.Replace(SubKey, this, cacheValue))
{
// put also in reverseMap
outerInstance.ReverseMap[cacheValue] = true;
}
else
{
throw new AssertionError("Should not reach here");
}
// successfully replaced us with new CacheValue -> return the value
// wrapped by it
return(value);
}
}