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https://github.com/sockspls/badfish
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c8213ba0d0
This commit builds on the work and ideas of #5345, #5348, and #5364. Place as much as possible of the TT implementation in tt.cpp, rather than in the header. Some commentary is added to better document the public interface. Fix the search read-TT races, or at least contain them to within TT methods only. Passed SMP STC: https://tests.stockfishchess.org/tests/view/666134ab91e372763104b443 LLR: 2.94 (-2.94,2.94) <-1.75,0.25> Total: 512552 W: 132387 L: 132676 D: 247489 Ptnml(0-2): 469, 58429, 138771, 58136, 471 The unmerged version has bench identical to the other PR (see also #5348) and therefore those same-functionality tests: SMP LTC: https://tests.stockfishchess.org/tests/view/665c7021fd45fb0f907c214a SMP LTC: https://tests.stockfishchess.org/tests/view/665d28a7fd45fb0f907c5495 closes https://github.com/official-stockfish/Stockfish/pull/5369 bench 1205675
98 lines
3.4 KiB
C++
98 lines
3.4 KiB
C++
/*
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Stockfish, a UCI chess playing engine derived from Glaurung 2.1
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Copyright (C) 2004-2024 The Stockfish developers (see AUTHORS file)
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Stockfish is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Stockfish is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef TT_H_INCLUDED
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#define TT_H_INCLUDED
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#include <cstddef>
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#include <cstdint>
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#include <tuple>
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#include "memory.h"
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#include "types.h"
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namespace Stockfish {
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class ThreadPool;
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struct TTEntry;
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struct Cluster;
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// There is only one global hash table for the engine and all its threads. For chess in particular, we even allow racy
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// updates between threads to and from the TT, as taking the time to synchronize access would cost thinking time and
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// thus elo. As a hash table, collisions are possible and may cause chess playing issues (bizarre blunders, faulty mate
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// reports, etc). Fixing these also loses elo; however such risk decreases quickly with larger TT size.
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//
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// `probe` is the primary method: given a board position, we lookup its entry in the table, and return a tuple of:
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// 1) whether the entry already has this position
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// 2) a copy of the prior data (if any) (may be inconsistent due to read races)
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// 3) a writer object to this entry
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// The copied data and the writer are separated to maintain clear boundaries between local vs global objects.
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// A copy of the data already in the entry (possibly collided). `probe` may be racy, resulting in inconsistent data.
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struct TTData {
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Move move;
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Value value, eval;
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Depth depth;
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Bound bound;
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bool is_pv;
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};
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// This is used to make racy writes to the global TT.
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struct TTWriter {
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public:
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void write(Key k, Value v, bool pv, Bound b, Depth d, Move m, Value ev, uint8_t generation8);
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private:
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friend class TranspositionTable;
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TTEntry* entry;
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TTWriter(TTEntry* tte);
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};
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class TranspositionTable {
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public:
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~TranspositionTable() { aligned_large_pages_free(table); }
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void resize(size_t mbSize, ThreadPool& threads); // Set TT size
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void clear(ThreadPool& threads); // Re-initialize memory, multithreaded
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int hashfull()
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const; // Approximate what fraction of entries (permille) have been written to during this root search
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void
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new_search(); // This must be called at the beginning of each root search to track entry aging
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uint8_t generation() const; // The current age, used when writing new data to the TT
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std::tuple<bool, TTData, TTWriter>
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probe(const Key key) const; // The main method, whose retvals separate local vs global objects
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TTEntry* first_entry(const Key key)
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const; // This is the hash function; its only external use is memory prefetching.
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private:
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friend struct TTEntry;
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size_t clusterCount;
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Cluster* table = nullptr;
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uint8_t generation8 = 0; // Size must be not bigger than TTEntry::genBound8
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};
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} // namespace Stockfish
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#endif // #ifndef TT_H_INCLUDED
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