In large-scale distributed actor runtimes spanning dozens of physical nodes, managing entity lifecycles across network boundaries presents complex challenges. If actors maintain cross-node references to one another, traditional local tracing GC cannot identify isolated distributed cycles. Distributed Garbage Collection (DGC) combines weighted reference counting with epoch-based lease renewals and distributed cycle-detection tokens to reclaim orphaned clusters without global stop-the-world pauses.
The Architecture of Distributed Cycle Detection
How weighted reference tokens and trial deletion detect unreachable cross-node actor loops:
In Weighted Reference Counting (WRC), the root actor initializes with a total weight W (e.g. 2^16). When duplicating an actor reference across network boundaries, the sender divides its weight in half between itself and the recipient. When a remote handle is destroyed, its weight is returned via a single asynchronous message. The actor terminates safely when its returned weight sum exactly equals W, eliminating chatty reference increments.
Distributed Memory Reclamation Protocols Compared
| DGC Algorithm | Message Overhead | Handles Network Partitions | Reclaims Distributed Cycles |
|---|---|---|---|
| Direct RPC Ref Counting | 2 RPCs per handle share | No (Risk of premature deallocation) | No (Permanent leak) |
| Lease-Based Timers (LBT) | Periodic heartbeat ping | Yes (Self-healing on timeout) | No (Cycles keep leases alive) |
| WRC + Trial Deletion Tokens | 1 message on final free | Yes (With epoch leases) | Yes (Identifies zero-external cycles) |
Distributed Actor Handle with Weighted Reference Counting in TypeScript
Managing remote reference weights and asynchronous termination:
export class RemoteActorHandle {
public readonly actorId: string;
public readonly hostNodeId: string;
private currentWeight: number;
constructor(actorId: string, hostNodeId: string, initialWeight: number = 65536) {
this.actorId = actorId;
this.hostNodeId = hostNodeId;
this.currentWeight = initialWeight;
}
// Split weight for remote replication
public cloneHandle(): RemoteActorHandle {
if (this.currentWeight <= 1) {
throw new Error('Weighted reference underflow: Weight cannot be split further');
}
const halfWeight = Math.floor(this.currentWeight / 2);
this.currentWeight -= halfWeight;
return new RemoteActorHandle(this.actorId, this.hostNodeId, halfWeight);
}
// Release handle and return weight to host node
public release(transportClient: { sendWeightReturn: (nodeId: string, actorId: string, weight: number) => void }): void {
transportClient.sendWeightReturn(this.hostNodeId, this.actorId, this.currentWeight);
this.currentWeight = 0;
}
}Explore Advanced Distributed Systems Engineering
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