src: free placeholder nodes for cppgc wrappers in MemoryTracker - #65793
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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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Every heap snapshot (
v8.getHeapSnapshot(),--heapsnapshot-near-heap-limit, the inspector) leaks oneMemoryRetainerNodeper livevm.Scriptorvmcontext:MemoryTracker::AddNode(const CppgcMixin*)allocates a placeholder that only stands in for the wrapper's JS node whileMemoryInfo()runs and, unlike the other node kinds, never hands it to the graph or frees it.The tracker now owns those placeholders and frees them when it is destroyed, and the already-seen branch of
Track(const CppgcMixin*)links to the wrapper's JS node like the first visit so the graph never points at a placeholder.Tests:
EnvironmentTest.HeapSnapshotWithCppgcWrappersDoesNotLeak(LSAN before); the heapsnapshot/heapdump suites pass.Refs: #56534
Disclosure: the code, test and this description were written by Claude Code, directed and reviewed by @codebytere.