fix(runtime): finalizer-safe handle ownership and deferred JSBlock teardown - #457
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…erred JSBlock teardown An in-flight kFinalizer callback could have its state freed or its node reset underneath it, breaking the contract that a finalizer either resets its handle or re-arms it and corrupting the drain's bookkeeping (the production V8_Fatal CHECKs on worker isolates). ObjectWeakCallbackState now has exactly two deleting sites -- FinalizerCallback's disposed branch and DisposeAllRegistered -- and every other retirement resets the persistent first, which frees the node, clears the pending bit and guarantees no further callback. A disposing flag makes a reentrant retirement (a -dealloc reached from DisposeValue calling __releaseNativeCounterpart) defer to the frame that owns the state. FinalizerCallback re-checks handle emptiness after DisposeValue: an adapter dealloc can reset the very persistent being finalized, and ClearWeak on an empty handle writes through a dead slot, so a handle emptied underneath its callback is retired, never re-armed. __releaseNativeCounterpart gains its missing Reset -- it retired registrations by deleting the state while leaving the node rooted forever with parameter() dangling at freed memory. The JSBlock dispose helper no longer does V8 work inline: the last native release can land on any thread, including inside the finalizer drain via dealloc cascades, so handle teardown posts to the owning isolate's event loop (a refused post means the isolate is gone and only native memory remains). The block pointer is cleared synchronously, and marshalling builds a fresh block for a wrapper whose JSBlock already died. Removes DisposerPHV (dead since VisitHandlesWithClassIds went away) and an unlocked, guardless Reset in NSDataAdapter's dealloc. Suite green; new GCFinalizerTests specs cover the retired-handle collectability contract, dealloc-cascade reentrancy, and the natively-held-block production shape. Reverting only the added Reset crashes the runtime outright.
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Included review availability: Your plan provides up to 2 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe runtime updates object finalization for reentrant disposal, performs JSBlock cleanup synchronously, adjusts block remarshal behavior, removes the obsolete persistent-handle visitor, and adds garbage-collection coverage. ChangesRuntime disposal lifecycle
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🟡 Moderate · up to The PR improves finalizer-safe handle ownership and deferred teardown, but a separate race between native release and JavaScript re-marshalling can still copy a block after its last release, potentially causing a runtime crash. Merge should wait for this bounded correctness issue to be fixed or explicitly accepted by the owner. Sequence Diagram(s)sequenceDiagram
participant V8
participant ObjectManager
participant ObjCObject
participant JSBlock
V8->>ObjectManager: invoke finalizer
ObjectManager->>ObjCObject: dispose native counterpart
ObjCObject->>ObjectManager: reentrant release callback
ObjectManager->>V8: reset or re-arm handle
JSBlock->>V8: synchronously reset callback persistent
Suggested reviewers: Poem
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 20.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 10 functions across 5 files. (2 skipped: 2 unsupported.)
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In `@NativeScript/runtime/Interop.mm`:
- Around line 548-558: Synchronize access to the block pointer between
BlockWrapper::ClearBlock() and Interop::WriteValue before calling Block_copy,
ensuring the pointer cannot be cleared or released after the null check but
before the copy. Use the existing lifetime or locking mechanism, and keep the
cleared-wrapper behavior intact.
In `@NativeScript/runtime/ObjectManager.mm`:
- Around line 113-115: Update FinalizerCallback to detect an already-disposing
state before disposing it, re-arm or reset its V8 weak handle as required, and
return ownership to DisposeAllRegistered so that it performs clearing,
resetting, and deletion without a use-after-free. Add a regression test covering
nested __collect() triggered from -dealloc.
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📒 Files selected for processing (11)
NativeScript/runtime/ArgConverter.hNativeScript/runtime/DataWrapper.hNativeScript/runtime/DisposerPHV.hNativeScript/runtime/DisposerPHV.mmNativeScript/runtime/Interop.mmNativeScript/runtime/NSDataAdapter.mmNativeScript/runtime/ObjectManager.hNativeScript/runtime/ObjectManager.mmTestRunner/app/tests/GCFinalizerTests.jsdocs/knowledge/v8-14-migration.mdv8ios.xcodeproj/project.pbxproj
💤 Files with no reviewable changes (4)
- NativeScript/runtime/DisposerPHV.mm
- v8ios.xcodeproj/project.pbxproj
- NativeScript/runtime/DisposerPHV.h
- NativeScript/runtime/NSDataAdapter.mm
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…'s claim The dispose helper goes back to inline teardown under the isolate Locker: callback_ is a strong, unregistered persistent, so resetting it never touches the finalizer drain's bookkeeping, and a foreign-thread Locker into the block's own isolate is legitimate now that extended class names are worker-scoped. The deferred posting -- and the cleared-block re-marshal machinery it required -- is removed; the unconditional callback_ Reset stays, since an already-detached callback still owns its node. FinalizerCallback now honors the disposing claim on entry: a nested collection during DisposeAllRegistered's walk can condemn a pre-claimed state, and disposing it there would free memory the walk still holds. The callback re-arms its node -- satisfying the finalizer contract -- and leaves clear, reset and delete to the owner. Block-collectability specs poll instead of assuming a single tick suffices; drain interleaving makes one tick a coin flip either way.
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Fixes the production
V8_Fatalcrashes on worker isolates (CHECK: "Finalizer callback must either reset its handle or re-arm it"atglobal-handles.cc:985, and its siblingCHECK(node->IsInUse())at:284) — nondeterministic global-handle-table corruption surfacing at whichever consistency CHECK trips first.Root cause
The custom
WeakCallbackType::kFinalizer(v8-buildscripts patch) requires a finalizer callback to either reset its handle or re-arm it. Several runtime paths could mutate a registered handle's state out from under an in-flight finalizer, breaking that contract:8080bc06balanced block ownership, blocks actually die — running a dispose helper that did V8 global-handle work inline on whatever thread the last native release happened, including insideObjectManager's finalizer drain via-dealloccascades, and from foreign threads (the cross-isolate Locker hazard of Deadlock: TS-extended class +initialize (v8::Locker) vs cross-isolate ObjC→JS callbacks wedges the app (root cause of the 600s CI test timeouts) #420).ArrayAdapter/NSDataAdapter/DictionaryAdapterdeallocs reset the very persistent whose finalizer is running (reached throughDisposeValue's[target release]), freeing the drained node under its own callback — the resurrect branch then calledClearWeak()on an empty handle, which V8 executes with no emptiness guard.__releaseNativeCounterpart: retired a registration withClearWeak+delete statebut noReset— leaking the node as a permanent strong root withparameter()dangling at freed state, and JS-callable so it could free the state under an in-flight callback.The fix: one ownership rule
ObjectWeakCallbackStateis deleted by exactly two sites (FinalizerCallback's disposed branch,DisposeAllRegistered); every other retirement resets the persistent first — freeing the node, clearing the pending bit, guaranteeing no further callback — enforced by adisposing_flag that makes reentrant retirement defer to the owning frame.FinalizerCallbackre-checks handle emptiness afterDisposeValueand retires (never re-arms) a handle whose node died underneath it. The JSBlock dispose helper stays inline — with the facts checked, that's sound:callback_is a strong, unregistered persistent (resetting it can't touch the drain's bookkeeping), and a foreign-thread Locker into the block's own isolate is legitimate now that extended class names are worker-scoped. The helper keeps one real fix: the previously-conditionalcallback_->Reset()no longer leaks the node when the callback was already detached.FinalizerCallbackalso honors thedisposing_claim on entry, so a nested collection during teardown can't free a state theDisposeAllRegisteredwalk still holds.DisposerPHV(dead code, same hazardous shape) is deleted; an unlocked, guardlessResetinNSDataAdapter's dealloc is removed.The reentrancy analysis (all six orderings) is in the commit; the correctness argument is the invariant, not the tests — none of these orderings can be fired deterministically from JS.
Tests
Five new specs in
GCFinalizerTests.js, including a discriminating one (aWeakRefto a__releaseNativeCounterpart-retired object must be collectible — impossible pre-fix) and the production shape (JS closure → ObjC block held natively → released by a GC finalizer → deferred teardown makes the closure collectible). Control run: reverting only the one-lineResetcrashes the runtime outright.Not fixed here (documented follow-ups)
DictionaryAdapternever resetsobject_→ strong-node leak pinning its JS object (needs its own analysis: the keys enumerator shares the handle).ArgConverter::MethodCallback) — separate investigation.Summary by CodeRabbit
Bug Fixes
Tests
Documentation