A FontStrike is the keeper of scaled glyph image data which is expensive to compute so needs to be cached. So long as that data may be being used it cannot be invalidated. Yet we also need to limit the amount of native memory and number of strike objects in use. For scalability and ease of use, a key goal is multi-threaded read access to a strike, so that it may be shared by multiple client objects, potentially executing on different threads, with no special reference counting or "check-out/check-in" requirements which would pass on the burden of keeping track of strike references to the SG2D and other clients. A cache of strikes is maintained via Reference objects. This helps in two ways : 1. The VM will free references when memory is low or they have not been used in a long time. 2. Reference queues provide a way to get notification of this so we can free native memory resources.