feat: add AllocEvent and FreeEvent to trace format#420
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Adds wire-format definitions for sampled allocation and matching free
events
that the upcoming memory profiler will emit. Per design §3:
- AllocEvent { timestamp_ns, tid, size, addr, callchain }
- FreeEvent { timestamp_ns, tid, addr, size, alloc_timestamp_ns }
`size` and `alloc_timestamp_ns` are denormalized onto FreeEvent so leak
analysis stays useful when the matching AllocEvent has been evicted by
trace
rotation.
This is the schema only — no producer (allocator hook) and no UI
flamegraph
yet. Both will land in later commits per the rollout in design §15.
Demo trace not regenerated: there is no producer of these events yet.
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yulnr
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May 18, 2026
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yulnr
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Looks good!
Side note: I wonder if we eventually want to make TelemetryEvent #[non_exhaustive]. Though I guess often new additions here mean breaking changes either way, and perhaps for the analysis tool you would like to be aware of new events rather than skip them.
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yeah we definitely want to make that |
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Adds wire-format definitions for sampled allocation and matching free events that the upcoming memory profiler will emit. Per design §3:
AllocEvent { timestamp_ns, tid, size, addr, callchain }FreeEvent { timestamp_ns, tid, addr, size, alloc_timestamp_ns }sizeandalloc_timestamp_nsare denormalized ontoFreeEventso leak analysis stays useful when the matchingAllocEventhas been evicted by trace rotation.This is the schema only — no producer (allocator hook) and no UI flamegraph yet. Both will land in follow-up PRs (ring-buffer scaffold,
Dial9Allocatorwrapper,MemoryProfiler::install, hook wiring) per the rollout in design §15.API shape
Both events are gated on
#[cfg_attr(not(feature = "unstable-events"), non_exhaustive)]. By default (no feature) they cannot be constructed by downstream crates, so adding fields later is non-breaking. Crates that need to construct them directly (e.g. for tests or custom event injection) opt in tounstable-eventsand accept that new fields may break them.Backwards compatibility
Per AGENTS.md trace-format rules: this PR only adds new event types. Old traces don't contain
AllocEvent/FreeEvent, the JS decoder gracefully no-ops on missing schemas, and we don't need old Rust decoders to read new traces.Demo trace
Not regenerated — there is no producer of these events yet.
Verification
cargo fmt --check: cleancargo clippy --all-targets --all-features: cleancargo nextest run: 594/594 passedcargo nextest run --stress-duration 20s: 2 iterations × 594/594 passed