src: free placeholder nodes for cppgc wrappers in MemoryTracker - #65793
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src: free placeholder nodes for cppgc wrappers in MemoryTracker#65793codebytere wants to merge 1 commit into
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`MemoryTracker::AddNode(const CppgcMixin*)` allocates a `MemoryRetainerNode` that only stands in for the wrapper's JS node while its `MemoryInfo()` runs; unlike the other node kinds it is not handed to the `EmbedderGraph`, and nothing freed it. Every heap snapshot (or other `BuildEmbedderGraph` call) leaked one node per live `vm.Script` or `vm` context. Keep the placeholders in the tracker and free them with it, and make the already-seen path in `Track(const CppgcMixin*)` add its edge to the wrapper's JS node like the first visit does, so the graph never refers to a placeholder. Refs: nodejs#56534 Signed-off-by: Shelley Vohr <shelley.vohr@gmail.com>
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## main #65793 +/- ##
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+ Coverage 89.99% 90.14% +0.14%
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Files 757 769 +12
Lines 257739 261450 +3711
Branches 48881 49644 +763
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+ Hits 231961 235685 +3724
+ Misses 16861 16786 -75
- Partials 8917 8979 +62
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MemoryTracker::AddNode(const CppgcMixin*)allocates aMemoryRetainerNodethat only stands in for the wrapper's JS node on the tracker's stack whileMemoryInfo()runs (the comment inTrack()calls it a dummy). The otherAddNode()overloads hand their node to thev8::EmbedderGraph, which owns it; this one does not, and nothing else freed it. Every heap snapshot,--heapsnapshot-near-heap-limittrigger or inspectorHeapProfiler.takeHeapSnapshotleaked 56 bytes per livevm.Script/vmcontext:node -e "globalThis.s = new vm.Script('1'); v8.getHeapSnapshot()"under LSAN shows it.The tracker now owns these placeholders and frees them when it is destroyed; its constructor and destructor move to
memory_tracker-inl.hbecause the member needs the completeMemoryRetainerNodetype. The already-seen branch ofTrack(const CppgcMixin*)adds its edge to the wrapper's JS node like the first visit does, so nothing in the graph ever points at a placeholder.Tests:
EnvironmentTest.HeapSnapshotWithCppgcWrappersDoesNotLeaktakes a heap snapshot from C++ with avm.Scriptand a context alive; LeakSanitizer reports the nodes before and is clean after (it asserts nothing without LSAN).test-heapsnapshot*,test-v8-*heap*,test-heapdump*andpummel/test-heapdump-vm-scriptpass.Refs: #56534
Disclosure: the code, test and this description were written by Claude Code, directed and reviewed by @codebytere.