Deno Runtime and V8 FinalizationRegistry: External Resource Cleanup Timing

Resource Management at the Runtime Boundary

Deno manages memory via the V8 engine's garbage collector, but external resources—such as those handled through the internal Ops layer—require precise cleanup to avoid memory leaks in the native layer.

While FinalizationRegistry is used to schedule the release of these external resources when the corresponding JavaScript object is reclaimed, the exact timing of this process remains a point of uncertainty. Because garbage collection is non-deterministic, there is a potential gap between the object becoming unreachable in the V8 heap and the actual execution of the cleanup callback for the native resource.

In high-throughput environments using Deno 2.0+, this latency can lead to temporary resource exhaustion before the collector triggers.

• Does the Deno runtime provide a mechanism to force the cleanup of FinalizationRegistry callbacks for native Ops without waiting for a full GC cycle?
• How does the runtime ensure the ordering of resource disposal when multiple interdependent external handles are registered?