Distributed garbage collection for general graphs

Steven R. Brandt, Hari Krishnan, Costas Busch, Gokarna Sharma

Abstract: We propose a scalable, cycle-collecting, decentralized, reference counting garbage collector with partial tracing. The algorithm is based on the Brownbridge system but uses four different types of references to label edges. Memory usage is O (log n) bits per node, where n is the number of nodes in the graph. The algorithm assumes an asynchronous network model with a reliable reordering channel. It collects garbage in O (E a ) time, where E a is the number of edges in the in- duced subgraph. The algorithm uses termination detection to manage the distributed computation, a unique identifier to break the symmetry among multiple collectors, and a transaction-based approach when multiple collectors conflict. Unlike existing algorithms, ours is not centralized, does not require barriers, does not require migration of nodes, does not require back-pointers on every edge, and is stable against concurrent mutation.