Add H1 dealloc hook and record_dealloc machinery (Phase 3.1) - #6
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- New snmalloc::profile::record_dealloc<Config>(void*) free function in src/snmalloc/profile/record.h. Compiles to a no-op for configs whose ClientMeta is not LazyArrayClientMetaDataProvider<SampledAlloc-slot>, so the default snmalloc::Config sees zero cost. - record_dealloc body splits into find_profile_slot (Config-specific pagemap walk) and clear_profile_slot (Config-agnostic atomic-CAS + SampledList::remove + NodePool::release), with the latter callable directly from tests. - H1 hook installed at the dealloc waist in Allocator::dealloc(void*) (mem/corealloc.h:1025), gated by SNMALLOC_PROFILE. Fires before any existing dealloc logic so profile-side cleanup observes the live pagemap, and is itself safe under recursive entry via the per-thread ReentrancyGuard. - record.h is intentionally lightweight; including commonconfig.h there would create a cycle (commonconfig -> mem/mem -> corealloc -> record). Instead corealloc.h forward-declares the template, and backend_helpers/backend_helpers.h pulls the full definition in once LazyArrayClientMetaDataProvider is visible. - record_alloc stays a stub: full alloc-side wiring lands in Phase 3.3. - New test src/test/func/profile_record/profile_record.cc covers the null-slot no-op, populated-slot drain, multi-threaded double-free CAS race, default-config compile-time no-op, ReentrancyGuard short-circuit and end-to-end libc::malloc/libc::free crash-freedom. - Default (OFF) build remains byte-identical to pre-Phase-3.1: the H1 call site is behind #ifdef SNMALLOC_PROFILE, and SNMALLOC_PROFILE=ON with the default NoClientMetaDataProvider Config inlines the if-constexpr branch into nothing (verified: same binary size for the default-config test executable in OFF vs ON builds). - All existing tests pass under both -DSNMALLOC_PROFILE=OFF (88/88) and -DSNMALLOC_PROFILE=ON (88/88), -fast and -check variants.
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Summary
Phase 3.1 — H1 dealloc hook at the waist (
Allocator::dealloc, 100% of public free entry points). Gated bySNMALLOC_PROFILE. Default (OFF) build is byte-identical.snmalloc::profile::record_dealloc<Config>(void*)insrc/snmalloc/profile/record.h. Compiles to no-op whenConfig::ClientMetais notLazyArrayClientMetaDataProvider<SampledAlloc*>slot type.find_profile_slot(Config-specific pagemap walk) +clear_profile_slot(Config-agnostic atomic-CAS +SampledList::remove+NodePool::release). Second function unit-testable without a real Backend.corealloc.h:1025, fires BEFORE existing dealloc logic so profile cleanup sees live pagemap entry. Re-entrancy-safe viaReentrancyGuard.record.his intentionally lightweight (forward-declared incorealloc.h, full definition pulled in bybackend_helpers.honceLazyArrayClientMetaDataProvidervisible) — avoids cyclecommonconfig.h → mem/mem.h → corealloc.h → record.h.record_allocstays a stub; full alloc-side wiring is Phase 3.3.Test plan
SNMALLOC_PROFILE=OFF(default)SNMALLOC_PROFILE=ONfunc-malloc-fasttest binary byte-identical OFF vs ON (216240 bytes)test_clear_null_slot— clear on null is no-optest_clear_populated_slot— published sample → cleared → live count drops, second clear no-optest_double_free_race— 2048 iters × 2 threads, exactly one CAS winner eachtest_default_config_compiletime_noop—static_assert(!config_has_profile_slot_v<snmalloc::Config>)test_reentrancy_short_circuit— slot untouched whileprofile_in_progress=1test_e2e_dealloc_does_not_crash— 1024 mixed-size libc malloc/free pairs through H1Ticket: 86ahrfww6