This class implements the global state of a simple sticky mark bits collector, based on an immix collector. The sticky mark bits algorithm is due to Demmers et al. (http://doi.acm.org/10.1145/96709.96735), and allows generational collection to be performed in a non-moving heap by overloading the role of mark bits to also indicate whether an object is new (nursery) or not. Thus nursery objects are identified by a bit in their header, not by where they lie within the address space. While Demmers et al. did their work in a conservative collector, here we have an exact collector, so we can use a regular write barrier, and don't need to use page protection etc. See the PLDI'08 paper by Blackburn and McKinley for a description of the algorithm: http://doi.acm.org/10.1145/1375581.1375586 All plans make a clear distinction between global and thread-local activities, and divides global and local state into separate class hierarchies. Global activities must be synchronized, whereas no synchronization is required for thread-local activities. There is a single instance of Plan (or the appropriate sub-class), and a 1:1 mapping of PlanLocal to "kernel threads" (aka CPUs or in Jikes RVM, Processors). Thus instance methods of PlanLocal allow fast, unsychronized access to functions such as allocation and collection. The global instance defines and manages static resources (such as memory and virtual memory resources). This mapping of threads to instances is crucial to understanding the correctness and performance properties of MMTk plans.