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.