[JSC] CodeBlock aging: no clock reads on the compile/sweep paths - #547
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Stamp BaselineJITCode::m_ownerWentAwayAt with the end time of the last collection (the CodeBlock died in it; Heap already records it) instead of ApproximateTime::now() in every ~CodeBlock, drop the now() in the BaselineJITCode initializer (an entry always has an owner until a CodeBlock dies and stamps it), and compare against the current collection's start time in releaseUnusedSharedBaselineCode.
…t of the current one) so a CodeBlock destroyed during a collection's end phase cannot look a cycle older than it is
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Disabled knowledge base sources:
WalkthroughChangesBaseline JIT GC timestamps
Merge Risk: 🟡 Moderate · up to The change removes unnecessary clock reads but adds Bun-specific timestamp state and accessors that are not conditionally compiled, which can break non-Bun builds. Merge should wait until those declarations are guarded consistently. 🚥 Pre-merge checks | ✅ 3 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (3 passed)
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Inline comments:
In `@Source/JavaScriptCore/jit/BaselineJITCode.h`:
- Line 30: Guard the MonotonicTime include and the m_ownerWentAwayAt member in
BaselineJITCode with USE(BUN_JSC_ADDITIONS), matching the guards already
enclosing the related reader and writer so non-Bun builds exclude this timestamp
state.
Apply the same fix in `@Source/JavaScriptCore/heap/Heap.h` around lines 396 - 397:
The heap accessor is the second unconditional Bun-specific declaration covered
by the same guard requirement.
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Configuration used: Organization UI
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Run ID: 928e9dee-6c48-4ad5-b313-49ce67feda86
📒 Files selected for processing (4)
Source/JavaScriptCore/bytecode/CodeBlock.cppSource/JavaScriptCore/heap/Heap.cppSource/JavaScriptCore/heap/Heap.hSource/JavaScriptCore/jit/BaselineJITCode.h
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Follow-up to #546: it read
ApproximateTime::now()in everyBaselineJITCodeconstructor and every baseline~CodeBlock. Neither needs the clock — the heap already timestamps each collection and GC-cycle resolution is all the cache release wants.m_ownerWentAwayAtis now stamped withHeap::lastGCEndTime()(the CodeBlock died in that collection), has no initializer-time read (an entry always has an owner until some CodeBlock dies and stamps it), andreleaseUnusedSharedBaselineCodecompares againstm_currentGCStartTime. No behaviour change intended.