1. A method for collecting garbage in a computing environment, the method comprising: a) tracing a root object to any of its reachable objects in a population of objects; b) marking any of said objects referred to in step a); c) unmarking a marked card comprising any of said objects; d) tracing any marked object on said unmarked card to an unmarked referent object of said marked object; e) marking said unmarked referent object; f) tracing said referent object marked in step e) to any of its reachable objects; g) marking any of said objects referred to in step f); h) tracing any unmarked root object referent to any of its reachable objects; i) marking any of said objects referred to in step h); j) performing any of steps c)-g); and k) designating any unmarked object in said population of objects as available for reallocation, wherein any of steps a)-g) are performed upon said population of objects concurrently with the operation of a mutator upon said population of objects within said computing environment, and wherein any of steps h)-k) are performed upon said population of objects while no mutator operates upon said population of objects within said computing environment.