feat(profile): cache resolved symbols across symbolize() calls (CU-86aj3uw04) - #79
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Process-global, lazily-initialised `HashMap<usize, ResolvedFrame>` guarded by `OnceLock<Arc<Mutex<...>>>` memoizes `resolve_one`. First `HeapProfile::symbolize` pays the backtrace/gimli parse cost; later calls are a cache lookup per unique frame address. Motivation (CU-86aj3uw04): heap-profile-eval against :konfig_bin_heapprof showed ~17 MB transient Vec + ~20 ms self-CPU per /debug/heap-profile.pprof scrape, rooted at `backtrace::symbolize::gimli::macho::Object::parse`. Code addresses are stable for a process lifetime, so the answer is too. Surface: pub fn clear_symbol_cache(); // flush, keep cell Tests: symbol_cache_cell_stable_across_pprof_writes Arc-ptr equality symbol_cache_returns_equal_frame_on_second_call value equality
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What
Memoize
resolve_one(addr)behind a process-globalOnceLock<Arc<Mutex<HashMap<usize, ResolvedFrame>>>>.HeapProfile::symbolizenow hits the cache instead of re-runningbacktrace::resolveon every call. Newclear_symbol_cache()flushes contents without dropping the cell.Why
Heap-profile-eval against
:konfig_bin_heapprof(CU-86aj360ae, 2026-06-16) measured ~17 MB transient Vec + ~20 ms self-CPU per/debug/heap-profile.pprofscrape, rooted atbacktrace::symbolize::gimli::macho::Object::parse → Vec::reserve → __rust_realloc. Code addresses are stable within a process — first scrape pays parse cost, subsequent scrapes are free.CU-86aj35zev confirmed cost is intrinsic to the snmalloc-rs symbolicate path, not a downstream transitive.
Cost
Mutexlock +HashMaplookup per unique frame.Evidence
cargo test --features profiling,symbolicate --lib→ 42/42 pass.cargo build --features profiling(no symbolicate) → clean.symbol_cache_cell_stable_across_pprof_writes: Arc-ptr equality across twowrite_pprof_gzcalls + afterclear_symbol_cache.symbol_cache_returns_equal_frame_on_second_call: cached lookup matches fresh resolve.symbolize_resolves_known_function_namestill green.