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fix(runtime): wrap a JS block made by another isolate as a native block - #573
When JS passes a function where native code expects a block, the runtime builds a native block around it. When such a block comes back to JS, as a call result or as an argument to a JS-implemented method, Interop::GetResult recognises it and returns the original JS function.
It recognised the block by its descriptor, which is one static for the whole process. So the check meant "some NativeScript isolate made this block", and the function was then read from the block's Persistent using the calling isolate. A block can reach another isolate through native state the whole process shares: a static, a singleton, a shared object. When it did:
the calling isolate read another isolate's handle without that isolate's lock, and JS received a function object that lives in another heap. Using it crashed in V8 code;
once the owning worker was gone, the read was a use-after-free.
Fix
Only the isolate that made the block gets its function back. Any other isolate wraps it like any native block: Block_copy, an owning BlockWrapper, and a function that invokes the block. Calling that function goes through the block's native entry point, which already pins and locks the owning isolate, runs the JS function there, and returns a zeroed result once that isolate is gone. Passing the wrapping function back to native code hands over the same underlying block.
Isolates are compared by ID, not by address
IsolateWrapper::BelongsTo(isolate) compares the ID Caches::Init assigns (the wrapper's gateId_), which survives teardown and is never reused. A disposed isolate's address is reused by later isolates, so an address comparison takes a dead worker's block for the new worker's own.
That was checked, not assumed: with BelongsTo temporarily comparing addresses, the fourth reader worker landed on the dead worker's exact address and the read was a use-after-free under AddressSanitizer. With the ID comparison the same spec passes.
The stand-in Caches of an isolate that is gone reports -1, and real IDs start at 0. BelongsTo also requires the wrapper's own ID not to be -1, so two -1 values never count as the same isolate.
For a block from another isolate, the release now happens after the wrapper's own Block_copy, so it can't be the last reference at that point and the block's dispose helper can't run inside GetResult.
Not changed
Two isolates' locks can deadlock. Calling another isolate's block takes that isolate's lock while holding your own. That was already the case for any native code that calls a worker's block from the main thread. If isolate A calls B's function at the moment B calls A's, or one drops the last reference to the other's block while the other waits, the two threads can deadlock. No spec triggers it.
Collecting the function that wraps a foreign block can run the block's dispose helper on this thread, which pins and locks the owning isolate. That is the existing behaviour for any last release of a JS block on a foreign thread, and the dispose path is untouched.
IsolateWrapper::Pin() still decides "already entered" by address. Every caller follows it with IsValid() or IsTornDown(), which use the ID, so a reused address ends in a zeroed result or a skipped disposal.
Tests
Six new specs in BlockCacheRaceTests.js, with a process-wide block slot added to the TNSOwnedBlocks fixture:
a worker's block read on the main thread, unowned, owned and taken: calling it returns a value that depends on worker-only state, and the worker reports the calls. After the worker ends, every call returns 0, and the functions are dropped and collected;
the function wrapping a worker's block passed back to native code: it reaches the worker's function, and the worker reading the slot again gets its own original function back;
the main thread's block read and called in a worker;
same isolate, on the main thread and inside a worker: the block read back is still the very same function;
a block whose worker is gone, read by four later workers in a row: each gets a function that returns 0. Whether a reader lands on the dead worker's address depends on the allocator, so this one isn't fully deterministic; without the fix it fails every time regardless.
Results:
With the fix: 1943 specs, 0 failures; under AddressSanitizer, 1943 specs, 0 failures, 0 ASan reports.
Before the fix, under AddressSanitizer, every run crashed:
a worker thread died in V8-generated code while running a main-isolate function;
with that spec skipped, the main thread died using a pointer from the worker's heap;
with the first three skipped, heap-use-after-free in PersistentBase::Get under Interop::GetResult, reading the dead worker's handle.
Summary by CodeRabbit
Bug Fixes
Improved handling of callbacks shared between JavaScript workers. Callbacks from another worker are now wrapped for use across workers, while callbacks returned to their originating worker preserve their original function identity. Calls made after the originating worker has stopped return zero instead of relying on an unavailable runtime callback. Callbacks can also be passed back to their originating worker without losing their identity.
No actionable comments were generated in the recent review.
Walkthrough
Runtime block conversion now checks whether a runtime-created block belongs to the current isolate. Shared-block fixtures and tests cover cross-isolate calls, same-isolate function identity, and calls after worker termination.
IsolateWrapper adds a gate-ID ownership check. Interop::GetResult returns a runtime-created block’s callback directly only when the block belongs to the current isolate.
Shared-block fixture and cross-isolate tests TestFixtures/Marshalling/TNSAllocLog.h, TestFixtures/Marshalling/TNSAllocLog.m, TestRunner/app/tests/BlockCacheRaceTests.js
TNSOwnedBlocks adds synchronized operations to store, retrieve, take, and clear a shared block. Tests cover calls across isolates, same-isolate identity, and calls after worker termination.
This change makes blocks created by one isolate safe to call from another, and calls return zero once the owning isolate is gone. The author reports passing specs under AddressSanitizer. No actionable merge-blocking risk remains.
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The title names the main change: a JavaScript block created by another isolate is now wrapped as a native block instead of being returned as the original function. The raw summary confirms that Intero…
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The title names the main change: a JavaScript block created by another isolate is now wrapped as a native block instead of being returned as the original function. The raw summary confirms that Interop::GetResult now takes the wrapping path for blocks from other isolates, which matches the title. The fix prefix also fits the bug-focused PR objectives.
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A rabbit stores a block with care, Then shares it across workers there. Same-isolate calls keep their name, Other isolates wrap the same. When workers sleep, calls return zero, The rabbit hops off, a test-day hero.
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A block built from a JS function can reach another isolate through native
state shared by the whole process (a static, a singleton, a shared object).
When such a block came back to JS, as a call result or as an argument to a
JS-implemented method, GetResult recognised it by the process-wide JSBlock
descriptor and answered the function its Persistent held, reading another
isolate's handle in the calling isolate without that isolate's lock. The
function object lives in the other heap, so using it crashed in V8 code, and
once the owning worker was gone the read was a use-after-free.
Only the isolate that made the block now gets its function back. Any other
isolate wraps it like any native block: Block_copy plus an owning
BlockWrapper, and calling it goes through the block's entry point, which pins
and locks the owning isolate, runs the function there, and answers a zeroed
result once that isolate is gone. Passing that wrapper back to native code
hands over the same block.
Isolates are told apart by the id Caches::Init assigns, never by address: a
disposed worker isolate's address is reused by later isolates, so an address
check takes a dead worker's block for the new worker's own.
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Actionable comments posted: 1
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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Inline comments:
Review comments at @TestFixtures/Marshalling/TNSAllocLog.m:
- Line 146: Apply objc_precise_lifetime to the previous block variable and the
local in clearSharedBlock so ARC keeps each alive until after the slot lock is
released; preserve the existing locking and block replacement/clearing behavior.
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NativeScript/runtime/Interop.mm
NativeScript/runtime/IsolateWrapper.h
TestFixtures/Marshalling/TNSAllocLog.h
TestFixtures/Marshalling/TNSAllocLog.m
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…nder its lock
The fixture drops the slot's previous block after leaving its lock, because
a JS block's dispose helper waits for the owning isolate. ARC may release an
unused strong local at its last use, which is inside the lock; a precise
lifetime keeps the release where the code puts it.
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What
When JS passes a function where native code expects a block, the runtime builds a native block around it. When such a block comes back to JS, as a call result or as an argument to a JS-implemented method,
Interop::GetResultrecognises it and returns the original JS function.It recognised the block by its descriptor, which is one static for the whole process. So the check meant "some NativeScript isolate made this block", and the function was then read from the block's
Persistentusing the calling isolate. A block can reach another isolate through native state the whole process shares: a static, a singleton, a shared object. When it did:Fix
Only the isolate that made the block gets its function back. Any other isolate wraps it like any native block:
Block_copy, an owningBlockWrapper, and a function that invokes the block. Calling that function goes through the block's native entry point, which already pins and locks the owning isolate, runs the JS function there, and returns a zeroed result once that isolate is gone. Passing the wrapping function back to native code hands over the same underlying block.Isolates are compared by ID, not by address
IsolateWrapper::BelongsTo(isolate)compares the IDCaches::Initassigns (the wrapper'sgateId_), which survives teardown and is never reused. A disposed isolate's address is reused by later isolates, so an address comparison takes a dead worker's block for the new worker's own.That was checked, not assumed: with
BelongsTotemporarily comparing addresses, the fourth reader worker landed on the dead worker's exact address and the read was a use-after-free under AddressSanitizer. With the ID comparison the same spec passes.The stand-in
Cachesof an isolate that is gone reports -1, and real IDs start at 0.BelongsToalso requires the wrapper's own ID not to be -1, so two -1 values never count as the same isolate.The owned-result release from #569
For a block from another isolate, the release now happens after the wrapper's own
Block_copy, so it can't be the last reference at that point and the block's dispose helper can't run insideGetResult.Not changed
IsolateWrapper::Pin()still decides "already entered" by address. Every caller follows it withIsValid()orIsTornDown(), which use the ID, so a reused address ends in a zeroed result or a skipped disposal.Tests
Six new specs in
BlockCacheRaceTests.js, with a process-wide block slot added to theTNSOwnedBlocksfixture:Results:
PersistentBase::GetunderInterop::GetResult, reading the dead worker's handle.Summary by CodeRabbit