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fix(runtime): release wrappers made for JS methods called from native code - #564
Fixes several leaks where the runtime retained native objects, and the JS that referenced them, forever. The most visible case is @nativescript/core's ListView: every ListViewCell (and everything its JS state and native view tree reference) leaked, about one list page of cells per push/pop.
1. self of a JS method called from native code (the main leak)
When native code calls a JS-implemented method on an object JS has no wrapper for yet, MethodCallback wrapped self with CreateJsWrapper(…, skipGCRegistration = true). That gave it a strong Persistent with no finalizer, plus a retain, and nothing ever released either. This predates the flag: the 2019 code carried a TODO: We are creating a persistent object here that will never be GCed.
The typical trigger is a JS initializer. ListViewCell.new() and UITableView's dequeue both run UIKit's -init, which calls the JS-overridden initWithStyle:reuseIdentifier:.
Now the wrapper is registered like any other, but its handle is held strong while something besides the runtime's Instances entry retains the object, and made weak only once that entry is the sole owner:
ObjectManager::ReconcileOwnership applies the retain count. It runs from the retain/release swizzle of TypeScript-extended classes, on the transitions to and from a count of 1.
A GC prologue (major and incremental marking) reconciles every managed wrapper, using the first non-JS -retainCount. That covers .extend() classes, which have no swizzle, and any transition the swizzle misses.
DisposeValue refuses a managed wrapper whose live retain count is above 1, which covers a retain from another thread racing a collection. A refused handle is made strong again instead of being resurrected at every collection.
__releaseNativeCounterpart finds the state of a strong-held handle.
While native code owns the object, nothing changes from today: the wrapper is a strong root, so its JS state is kept and never goes through the resurrecting-finalizer path. Once native code lets go, the wrapper is collected and the object released.
An object reached from its own -dealloc (a JS override called during deallocation, detected through -allowsWeakReference) gets a borrowed wrapper: neither cached nor retaining, and detached by MethodCallback when the call returns. A this that JS keeps from such a call then reads as released (the released-object policy applies) instead of pointing at freed memory, and __releaseNativeCounterpart neither releases it nor frees it twice. The old code cached a pointer to an object about to be freed, because a retain can't keep a deallocating object alive.
2. Owned class-method and C-function returns that hit a cached wrapper
Interop::GetResult returned the cached wrapper without releasing the +1 of an owned return. The uncached path and ConstructObject already release it. The case that matters here: +new on a class with a JS initializer kept an extra retain, because the initializer had already wrapped the object.
The release is limited to class methods and C functions, which always return a real +1 when they own their result. Instance methods keep today's behavior, because some of them return without a net retain:
NS_REPLACES_RECEIVER methods such as -awakeAfterUsingCoder: return their receiver;
a JS-implemented owned-return method reached through native dispatch (a JS copyWithZone: behind -copy) returns at +0.
So an owned instance return that hits a cached wrapper, such as copy on an immutable object, still leaks one retain, as before. Fixing that needs JS implementations to return +1 to native callers, which is tracked in #566.
3. nativeException on errors built from an NSError or NSException
Both wrappers (added in #311 and #409) used skipGCRegistration = true, so every such error leaked its native error. They're registered normally now; the JS error's nativeException property keeps the wrapper alive for as long as the error is.
4. ~NativeScriptException never released its JS error
It deleted its v8::Persistent, which doesn't reset the handle (kResetInDestructor is false). So every JS error thrown through a NativeScriptException stayed reachable from (Global handles), including the one built from each NSException. The destructor now resets the handle while the isolate is alive. It takes the isolate's Locker if the current thread doesn't hold it, because event-loop tasks catch these exceptions after their Locker is gone.
Lifetime note
Objects first wrapped through a JS method called from native code were immortal before. Now they're collected like any other wrapper once nothing but the runtime retains them. Something native code holds only weakly or unretained (a delegate, a target) with no JS reference will now be collected, which can surface latent app bugs.
Tests
New NativeCallbackSelfTests.js. Each spec checks that state is kept while native code owns the object, and that the object is freed exactly once afterwards (counted deallocations or a weak NSHashTable):
JS init reached through +new, held by a native array;
JS init reached through +new, held only by JS;
cells UIKit creates from a registered .extend() class with a JS initWithStyle:reuseIdentifier:, owned by a superview, with their expandos read back after several collections;
__releaseNativeCounterpart on a managed wrapper, both while native code holds the object and while only JS does;
no over-release: -awakeAfterUsingCoder: returning its receiver, and a JS copyWithZone: reached through native -copy;
a this kept from a JS method run by -dealloc reads as released;
the NSError nativeException and the NSException nativeException: usable while the error lives, freed once it's collected.
Results:
With the fix: 1876 specs, 0 failures; under AddressSanitizer, 1876 specs, 0 failures, 0 ASan reports.
Negative control (main's runtime code with the original six specs): all six fail, only on the freeing checks. The state-keeping checks pass on main too, so that behavior is unchanged.
The first revision of this PR crashes on the new over-release specs, which is why the owned-return release was narrowed.
Summary by CodeRabbit
Bug Fixes
Improved object lifetime handling when native objects call JavaScript methods, including during deallocation.
Fixed cases where JavaScript state could be lost while native code still retained an object, or objects could remain alive after native ownership ended.
Corrected cleanup of returned objects and native errors so they remain usable while referenced and are released appropriately.
Improved exception cleanup when the JavaScript runtime is active or shutting down.
Tests
Added coverage for native callback lifetimes, ownership, returned objects, and error cleanup.
… code
When native code called a JS-implemented method on an object JS had no
wrapper for yet (a JS initializer run by +new or by UIKit, as with
@nativescript/core's ListView cells), MethodCallback wrapped `self` with
a strong, unregistered handle and a retain that were never released: the
object, its wrapper and everything its JS state referenced leaked.
The wrapper is now registered like any other, but its handle is held
strong while something besides the Instances entry retains the object and
made weak once that entry is the only owner. That is reconciled from the
retain/release swizzle of TypeScript-extended classes and, for every
class, when a major GC starts. Until native code lets go the wrapper
behaves as before (a strong root, so its JS state is kept); afterwards it
is collected and the object released. An object reached from its own
-dealloc gets a wrapper that is neither cached nor retaining.
Related leaks fixed alongside:
- Owned returns (new/alloc/copy families) that hit a cached wrapper now
give back their +1, as the uncached path and ConstructObject already
did; +new on a class with a JS initializer kept an extra retain.
- The nativeException wrapper attached to errors built from an NSError
or NSException was strong and never released; it is registered now.
- ~NativeScriptException deleted its Persistent without resetting it,
which leaks the V8 handle: every JS error thrown through it, and what it
references, stayed alive.
The runtime now tracks Objective-C wrapper ownership against V8 handle strength and reconciles it during callbacks and garbage collection. Native callback receivers and returned objects use updated wrapper lifecycle paths. New tests cover native and JavaScript ownership, UIKit cells, copies, and native exceptions.
Changes: Wrapper ownership lifecycle
Layer / File(s)
Summary
Ownership state and reconciliation NativeScript/runtime/ObjectManager.h, NativeScript/runtime/ObjectManager.mm, NativeScript/runtime/DataWrapper.h, NativeScript/runtime/ClassBuilder.h
ObjectManager tracks wrapper finalizer states and reconciles V8 handle strength with native retain counts. It clears tracking as states retire and limits non-final disposal when native retainers remain. ClassBuilder::FindNotOverridenMethod is now public.
Callback receiver and retain integration NativeScript/runtime/ArgConverter.h, NativeScript/runtime/ArgConverter.mm, NativeScript/runtime/ClassBuilder.mm, TestRunner/app/tests/NativeCallbackSelfTests.js, TestRunner/app/tests/index.js
MethodCallback uses WrapNativeCallbackSelf for native receivers. Retain and release callbacks reconcile managed wrappers. Tests cover native and JavaScript ownership and UIKit cell lifetimes.
Native return and exception cleanup NativeScript/runtime/Interop.h, NativeScript/runtime/Interop.mm, NativeScript/runtime/NativeScriptException.h, NativeScript/runtime/NativeScriptException.mm, TestRunner/app/tests/NativeCallbackSelfTests.js
Cached owned returns release the native result under the added condition. Exception wrappers use updated cleanup, and the exception destructor resets its persistent handle. Tests cover receiver and copy returns and native exception lifetimes.
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Title check
The title names the main change: the runtime now releases wrappers created when native code calls JavaScript-implemented methods. The raw summary and PR objectives both center on managing wrapper owne…
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Explanation
The title names the main change: the runtime now releases wrappers created when native code calls JavaScript-implemented methods. The raw summary and PR objectives both center on managing wrapper ownership for native-to-JS callbacks, with related fixes for borrowed wrappers, cached owned returns, and NativeScriptException cleanup. The title is specific and matches the changeset, so it passes.
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A rabbit checks the wrapper's hold, While native paws keep states controlled. V8 grows strong, then soft and light, Callbacks pass through day and night. The tests hop on; the paths are clear, And errors rest, then disappear.
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Files selected for processing: 10
NativeScript/runtime/ArgConverter.h
NativeScript/runtime/ArgConverter.mm
NativeScript/runtime/ClassBuilder.mm
NativeScript/runtime/DataWrapper.h
NativeScript/runtime/Interop.h
NativeScript/runtime/Interop.mm
NativeScript/runtime/NativeScriptException.h
NativeScript/runtime/NativeScriptException.mm
NativeScript/runtime/ObjectManager.mm
TestRunner/app/tests/NativeCallbackSelfTests.js
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NativeScript/runtime/NativeScriptException.h
NativeScript/runtime/NativeScriptException.mm
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Actionable comments posted: 2
Fix comments: Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @NativeScript/runtime/ArgConverter.mm:
- Line 1109: Update the TransientSelf allocation path to register each receiver
with the isolate’s teardown mechanism, using IsolateTracked or an equivalent
existing registry. Ensure teardown resets the handle and deletes the
ObjCDataWrapper while the isolate is still alive, and coordinate with
DisposeTransientSelf to prevent double deletion.
- Line 1110: Update the transient receiver cleanup associated with
DisposeTransientSelf so the borrowed native association is invalidated when the
native callback ends, rather than waiting for the JS receiver to be collected.
Ensure later calls through a retained receiver cannot pass the freed native
address to ArgConverter::Invoke, without changing the lifetime of independently
owned wrappers.
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Files selected for processing: 11
NativeScript/runtime/ArgConverter.h
NativeScript/runtime/ArgConverter.mm
NativeScript/runtime/ClassBuilder.h
NativeScript/runtime/ClassBuilder.mm
NativeScript/runtime/DataWrapper.h
NativeScript/runtime/Interop.mm
NativeScript/runtime/NativeScriptException.mm
NativeScript/runtime/ObjectManager.h
NativeScript/runtime/ObjectManager.mm
TestRunner/app/tests/NativeCallbackSelfTests.js
TestRunner/app/tests/index.js
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- Release a cached owned return's +1 only for class methods and C
functions. An instance method can return its receiver without a net
retain (NS_REPLACES_RECEIVER, e.g. -awakeAfterUsingCoder:) or come
from a JS implementation that returns at +0, and releasing those freed
live objects.
- Wrap a deallocating self in a borrowed wrapper that MethodCallback
detaches when the call returns, instead of one freed by a weak
callback: a `this` JS keeps reads as released rather than pointing at
the freed object, nothing is left behind at teardown, and
__releaseNativeCounterpart neither releases it nor frees it twice.
Deallocation is detected through -allowsWeakReference.
- __releaseNativeCounterpart retires a managed wrapper's own handle,
whatever Instances maps its object to.
- ~NativeScriptException releases its handle under the isolate's Locker
when the current thread does not hold it (event loop tasks catch after
their Locker is gone), and only while the isolate is alive.
- Reconcile with the same non-JS retain count everywhere, keep a refused
managed handle strong instead of re-arming it weak, and post the
off-thread reconcile after the real retain/release.
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What
Fixes several leaks where the runtime retained native objects, and the JS that referenced them, forever. The most visible case is
@nativescript/core'sListView: everyListViewCell(and everything its JS state and native view tree reference) leaked, about one list page of cells per push/pop.1.
selfof a JS method called from native code (the main leak)When native code calls a JS-implemented method on an object JS has no wrapper for yet,
MethodCallbackwrappedselfwithCreateJsWrapper(…, skipGCRegistration = true). That gave it a strongPersistentwith no finalizer, plus a retain, and nothing ever released either. This predates the flag: the 2019 code carried aTODO: We are creating a persistent object here that will never be GCed.The typical trigger is a JS initializer.
ListViewCell.new()andUITableView's dequeue both run UIKit's-init, which calls the JS-overriddeninitWithStyle:reuseIdentifier:.Now the wrapper is registered like any other, but its handle is held strong while something besides the runtime's
Instancesentry retains the object, and made weak only once that entry is the sole owner:ObjectManager::ReconcileOwnershipapplies the retain count. It runs from the retain/release swizzle of TypeScript-extended classes, on the transitions to and from a count of 1.-retainCount. That covers.extend()classes, which have no swizzle, and any transition the swizzle misses.DisposeValuerefuses a managed wrapper whose live retain count is above 1, which covers a retain from another thread racing a collection. A refused handle is made strong again instead of being resurrected at every collection.__releaseNativeCounterpartfinds the state of a strong-held handle.While native code owns the object, nothing changes from today: the wrapper is a strong root, so its JS state is kept and never goes through the resurrecting-finalizer path. Once native code lets go, the wrapper is collected and the object released.
An object reached from its own
-dealloc(a JS override called during deallocation, detected through-allowsWeakReference) gets a borrowed wrapper: neither cached nor retaining, and detached byMethodCallbackwhen the call returns. Athisthat JS keeps from such a call then reads as released (the released-object policy applies) instead of pointing at freed memory, and__releaseNativeCounterpartneither releases it nor frees it twice. The old code cached a pointer to an object about to be freed, because a retain can't keep a deallocating object alive.2. Owned class-method and C-function returns that hit a cached wrapper
Interop::GetResultreturned the cached wrapper without releasing the +1 of an owned return. The uncached path andConstructObjectalready release it. The case that matters here:+newon a class with a JS initializer kept an extra retain, because the initializer had already wrapped the object.The release is limited to class methods and C functions, which always return a real +1 when they own their result. Instance methods keep today's behavior, because some of them return without a net retain:
NS_REPLACES_RECEIVERmethods such as-awakeAfterUsingCoder:return their receiver;copyWithZone:behind-copy) returns at +0.So an owned instance return that hits a cached wrapper, such as
copyon an immutable object, still leaks one retain, as before. Fixing that needs JS implementations to return +1 to native callers, which is tracked in #566.3.
nativeExceptionon errors built from an NSError or NSExceptionBoth wrappers (added in #311 and #409) used
skipGCRegistration = true, so every such error leaked its native error. They're registered normally now; the JS error'snativeExceptionproperty keeps the wrapper alive for as long as the error is.4.
~NativeScriptExceptionnever released its JS errorIt
deleted itsv8::Persistent, which doesn't reset the handle (kResetInDestructoris false). So every JS error thrown through aNativeScriptExceptionstayed reachable from(Global handles), including the one built from each NSException. The destructor now resets the handle while the isolate is alive. It takes the isolate'sLockerif the current thread doesn't hold it, because event-loop tasks catch these exceptions after theirLockeris gone.Lifetime note
Objects first wrapped through a JS method called from native code were immortal before. Now they're collected like any other wrapper once nothing but the runtime retains them. Something native code holds only weakly or unretained (a delegate, a target) with no JS reference will now be collected, which can surface latent app bugs.
Tests
New
NativeCallbackSelfTests.js. Each spec checks that state is kept while native code owns the object, and that the object is freed exactly once afterwards (counted deallocations or a weakNSHashTable):initreached through+new, held by a native array;initreached through+new, held only by JS;.extend()class with a JSinitWithStyle:reuseIdentifier:, owned by a superview, with their expandos read back after several collections;__releaseNativeCounterparton a managed wrapper, both while native code holds the object and while only JS does;-awakeAfterUsingCoder:returning its receiver, and a JScopyWithZone:reached through native-copy;thiskept from a JS method run by-deallocreads as released;nativeExceptionand the NSExceptionnativeException: usable while the error lives, freed once it's collected.Results:
main's runtime code with the original six specs): all six fail, only on the freeing checks. The state-keeping checks pass onmaintoo, so that behavior is unchanged.Summary by CodeRabbit