[matthargett]

On V8, a garbage collection does not run N-API finalizers directly. The weak callback enqueues each finalizer on napi_env::pending_finalizers for a second pass that has to run from a safe host boundary, and the host owns draining that queue. JsRuntimeHost never drained it, so every collected wrapper (Napi::External, ObjectWrap, external array buffers) kept its native resources alive until the environment was torn down. Plugins that hand out many short-lived wrappers per frame, such as WebGPU buffers, textures and command encoders, leaked without bound.

Change

• AppRuntime::Run calls a new engine-specific DrainPostDispatchWork(Napi::Env) hook after each dispatcher turn that ran work. Running once per turn, rather than after each callback, keeps the drain off the per-callback path.
• On V8 the hook is Napi::DrainFinalizers, which pops finalizers from the pending queue one at a time (a finalizer may enqueue or dequeue others) and stops once an 8 ms budget is spent, so a large batch cannot monopolize the JavaScript thread; the remainder runs on the following turns.
• The hook is a no-op on Chakra, JavaScriptCore, QuickJS, Hermes and JSI, which finalize through their own mechanisms.

Tests

Two V8-only unit tests in Tests.AppRuntime.cpp, compiled under a new JSRUNTIMEHOST_NAPI_ENGINE_V8 definition in both unit-test CMake files:

• AppRuntime.V8FinalizersDrainAfterDispatch: the finalizers of 32 collected externals have all run by the dispatcher turn after the collection.
• AppRuntime.V8FinalizerDrainYieldsBetweenDispatcherTurns: a batch whose finalizers exceed the budget is spread across turns instead of completing in one, and completes within a bounded number of turns.

The JavaScriptCore build of AppRuntime, napi and JsRuntimeHostUnitTests passes its full suite on macOS.

Notes

This supersedes plugin-local workarounds such as the finalizer pump in the NativeDawn plugin (#1781), which reaches into napi_env internals from outside JsRuntimeHost.

Port of BabylonJS/JsRuntimeHost#217.

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