Lockless main hash table (Hyatt/Crafty scheme)

Replaces the sharded-spinlock protection around every main-hash probe
and store with the classic lockless-hashing technique: HASH_ENTRY's
existing 8-byte data word (mv/uDepth/bvFlags/iValue, now addressable
as u64Data via an anonymous union) and its 8-byte u64Sig are written
as two independent plain 64-bit stores -- u64Data first, then
u64Sig = realKey ^ u64Data -- instead of under a lock. Every probe
reads both words into a local snapshot and verifies
(storedSig ^ storedData) == realKey before trusting anything; a
concurrent writer racing a reader can only ever produce a
self-inconsistent pair that fails this check (an ordinary miss), not
corruption, except in the one documented, harmless case where the two
racing entries' data words happen to be bit-identical.

LockCompareExchange (the old spinlock's cost) was already showing up
at 0.51% self-time in a `bench` profile -- real, measured overhead on
a path hit roughly once per searched node, now removed.

HashLookup's contract changes from "return a pointer into the live
table, or NULL" to "return TRUE/FALSE, with *pOut holding a validated
local copy on TRUE" -- callers must never read back through a pointer
into the live table after this function returns, since there's no
longer a lock serializing that against a concurrent writer. The one
real caller (search.c) and the DEBUG-only VERIFY_HASH_HIT diagnostic
are updated accordingly.

testhash.c: AnalyzeFullHashTable's duplicate-entry check used to
compare two entries' raw u64Sig directly, which no longer means "same
position" now that u64Sig depends on each entry's own data word --
fixed to un-corrupt both sides first. Adds TestLocklessHashAlgebra, a
pure algebra test (no concurrency) verifying the XOR round-trip and
torn-write self-detection property over 200k random trials, wired
into the TEST=1 startup self-test suite.

Verified: TestLocklessHashAlgebra passes; single-threaded runs of the
locked and lockless binaries produce identical node counts and solve
scores across all three curated suites (ecm_ringers/confident_quick/
hard_quick); several minutes of real contention (tiny 4MB hash table,
12 threads at ~1200% CPU on a Ryzen 9 3900X, plus a 4-core run
locally) produced zero crashes/assertions/corruption on either
machine.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

0 files changed, 0 insertions, 0 deletions