GARBAGE COLLECTION USING A DYNAMIC THREATENING BOUNDARY

Generational techniques have been very successful in reducing the impa ct of garbage collection algorithms upon the performance of programs. However, all generational algorithms occasionally promote objects that later become garbage, resulting in an accumulation of garbage in olde r generations. Reclaiming this tenured garbage without resorting to co llecting the entire heap is a difficult problem. In this paper, we des cribe a mechanism that extends existing generational collection algori thms by allowing them to reclaim tenured garbage more effectively. In particular, our dynamic threatening boundary mechanism divides memory into two spaces, one for short-lived, and another for long-lived objec ts. Unlike previous work, our collection mechanism can dynamically adj ust the boundary between these two spaces either forward or backward i n time, essentially allowing data to become untenured. We describe an implementation of the dynamic threatening boundary mechanism and quant ify its associated costs. We also describe a policy for setting the th reatening boundary and evaluate its performance relative to existing g enerational collection algorithms. Our results show that a policy that uses the dynamic threatening boundary mechanism is effective at recla iming tenured garbage.