Gpars (Groovy Parallel Systems) is the best solution for your concurrency problems with mutable objects. Gpars gives you a number of high-level abstractions for writing concurrent and parallel code in Groovy (map/reduce, fork/join, asynchronous closures, actors, agents, dataflow concurrency and other concepts), which can make your Java and Groovy code concurrent and/or parallel with little effort. Gpars is bundled in Groovy starting from version of 2.1.