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This patch fixes an issue where if the return value of `sbrk(0)` ever changed after initially being set, we'd encounter a panic: the value is stored in a `PersistentRootedObject`, `AB`, which the code tries to initialize multiple times. Persistent roots can't only be initialized ones, after which they have to be `set`.
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I don't know how to build a reasonable test for this, but it fixes an issue we encountered in the real world. |
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Nice, I can imagine this must have been very tricky to track down. Thanks I wasn't aware of this persistent rooted behaviour! |
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Happy to merge, but for testing, what conditions would trigger it? Large memory use at Wizer time? |
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If so maybe it's as simple as a test with a large source text? |
guybedford
approved these changes
Jan 31, 2025
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It's happening at runtime, not during wizening. I think it might be related to malloc, not GC allocation, but that's hard to reduce |
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Right, so maybe a call with a very large buffer that causes a page size increase, followed by another call? |
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This patch fixes an issue where if the return value of
sbrk(0)ever changed after initially being set, we'd encounter a panic: the value is stored in aPersistentRootedObject,AB, which the code tries to initialize multiple times. Persistent roots can't only be initialized ones, after which they have to beset.