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Change all node counters to use relaxed loading #309

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Merged
kevlu8 merged 1 commit into from
May 9, 2026
Merged

Change all node counters to use relaxed loading #309

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30 changes: 17 additions & 13 deletions engine/search.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ std::stringstream last_line;
uint16_t num_threads = 1;

std::atomic<uint64_t> nodecnt[64][64] = {{}};
std::atomic<uint64_t> nodes[MAX_THREADS] = {};
alignas(64) std::atomic<uint64_t> nodes[MAX_THREADS] = {};
std::atomic<uint64_t> tbhits = 0;

uint64_t perft(Position &pos, int depth) {
Expand Down Expand Up @@ -192,14 +192,15 @@ bool is_valid_score(Value score) {
* - Late move reduction (instead of reducing depth, we reduce the search window) (not a known technique, maybe worth trying?)
*/
Value quiesce(Position &pos, ThreadInfo &ti, Value alpha, Value beta, int side, int ply, bool pv=false) {
nodes[ti.id]++;
nodes[ti.id].fetch_add(1, std::memory_order_relaxed);

if (pv) ti.pvlen[ply] = 0;

if (stop_search) return 0;

if (ti.is_main) {
if (!(nodes[ti.id] & 4095)) {
auto cur_nodes = nodes[ti.id].load(std::memory_order_relaxed);
if (!(cur_nodes & 4095)) {
// The time check is relatively expensive and thus only performed every 4096 nodes
auto time = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - start).count();
if (time > mxtime) {
Expand All @@ -208,10 +209,10 @@ Value quiesce(Position &pos, ThreadInfo &ti, Value alpha, Value beta, int side,
}
}

if (!do_softnodes && nodes[ti.id] > mx_nodes) {
if (!do_softnodes && cur_nodes > mx_nodes) {
stop_search = true;
return 0;
} else if (do_softnodes && mx_nodes < 1e15 && nodes[ti.id] > mx_nodes * 50) {
} else if (do_softnodes && mx_nodes < 1e15 && cur_nodes > mx_nodes * 50) {
stop_search = true;
return 0;
}
Expand Down Expand Up @@ -369,12 +370,13 @@ Value negamax(Position &pos, ThreadInfo &ti, int depth, Value alpha = -VALUE_INF
ti.seldepth = std::max(ti.seldepth, ply);
}

nodes[ti.id]++;
nodes[ti.id].fetch_add(1, std::memory_order_relaxed);

if (stop_search) return 0;

if (ti.is_main) {
if (!(nodes[ti.id] & 4095)) {
auto cur_nodes = nodes[ti.id].load(std::memory_order_relaxed);
if (!(cur_nodes & 4095)) {
// The time check is relatively expensive and thus only performed every 4096 nodes
auto time = std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now() - start).count();
if (time > mxtime) {
Expand All @@ -383,10 +385,10 @@ Value negamax(Position &pos, ThreadInfo &ti, int depth, Value alpha = -VALUE_INF
}
}

if (!do_softnodes && nodes[ti.id] > mx_nodes) {
if (!do_softnodes && cur_nodes > mx_nodes) {
stop_search = true;
return 0;
} else if (do_softnodes && mx_nodes < 1e15 && nodes[ti.id] > mx_nodes * 50) {
} else if (do_softnodes && mx_nodes < 1e15 && cur_nodes > mx_nodes * 50) {
stop_search = true;
return 0;
}
Expand Down Expand Up @@ -654,7 +656,8 @@ Value negamax(Position &pos, ThreadInfo &ti, int depth, Value alpha = -VALUE_INF
Move move = NullMove;
int i = 0;

uint64_t prev_nodes = nodes[ti.id];
uint64_t prev_nodes = 0;
if (root) prev_nodes = nodes[ti.id].load(std::memory_order_relaxed);

ti.line[ply+1].cutoffcnt = 0;

Expand Down Expand Up @@ -878,8 +881,9 @@ Value negamax(Position &pos, ThreadInfo &ti, int depth, Value alpha = -VALUE_INF
ti.line[ply].corr_hist = nullptr;

if (root) {
nodecnt[move.src()][move.dst()] += nodes[ti.id] - prev_nodes;
prev_nodes = nodes[ti.id];
auto cur_nodes = nodes[ti.id].load(std::memory_order_relaxed);
nodecnt[move.src()][move.dst()].fetch_add(cur_nodes - prev_nodes, std::memory_order_relaxed);
prev_nodes = cur_nodes;
}

if (stop_search)
Expand Down Expand Up @@ -1044,7 +1048,7 @@ void iterativedeepening(Position &pos, ThreadInfo &ti, int depth) {
uint64_t bm_nodes = nodecnt[best_move.src()][best_move.dst()];
uint64_t tot_nodes = 0;
for (int t = 0; t < num_threads; t++) {
tot_nodes += nodes[t]; // ig this is dangerous but whatever
tot_nodes += nodes[t].load(std::memory_order_relaxed); // ig this is dangerous but whatever
}

// UCI output from main thread only
Expand Down
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