X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=e008bec1e45d8a063cca7d05dd803411d7cb38c6;hp=50bce13c309370fa7859073be858121aa2948ff5;hb=217840a6a5a40b516cab59a450a9f36352997240;hpb=a9cca5c953e6ccec865102b13b47b9f45d98a0fc

diff --git a/src/search.cpp b/src/search.cpp
index 50bce13c..e008bec1 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -102,6 +102,48 @@ namespace {
     Move best = MOVE_NONE;
   };
 
+  // Breadcrumbs are used to mark nodes as being searched by a given thread.
+  struct Breadcrumb {
+    std::atomic<Thread*> thread;
+    std::atomic<Key> key;
+  };
+  std::array<Breadcrumb, 1024> breadcrumbs;
+
+  // ThreadHolding keeps track of which thread left breadcrumbs at the given node for potential reductions.
+  // A free node will be marked upon entering the moves loop, and unmarked upon leaving that loop, by the ctor/dtor of this struct.
+  struct ThreadHolding {
+    explicit ThreadHolding(Thread* thisThread, Key posKey, int ply) {
+       location = ply < 8 ? &breadcrumbs[posKey & (breadcrumbs.size() - 1)] : nullptr;
+       otherThread = false;
+       owning = false;
+       if (location)
+       {
+          // see if another already marked this location, if not, mark it ourselves.
+          Thread* tmp = (*location).thread.load(std::memory_order_relaxed);
+          if (tmp == nullptr)
+          {
+              (*location).thread.store(thisThread, std::memory_order_relaxed);
+              (*location).key.store(posKey, std::memory_order_relaxed);
+              owning = true;
+          }
+          else if (   tmp != thisThread
+                   && (*location).key.load(std::memory_order_relaxed) == posKey)
+              otherThread = true;
+       }
+    }
+
+    ~ThreadHolding() {
+       if (owning) // free the marked location.
+           (*location).thread.store(nullptr, std::memory_order_relaxed);
+    }
+
+    bool marked() { return otherThread; }
+
+    private:
+    Breadcrumb* location;
+    bool otherThread, owning;
+  };
+
   template <NodeType NT>
   Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
 
@@ -292,7 +334,7 @@ void Thread::search() {
   bestValue = delta = alpha = -VALUE_INFINITE;
   beta = VALUE_INFINITE;
 
-  size_t multiPV = Options["MultiPV"];
+  multiPV = Options["MultiPV"];
   Skill skill(Options["Skill Level"]);
 
   // When playing with strength handicap enable MultiPV search that we will
@@ -847,6 +889,9 @@ moves_loop: // When in check, search starts from here
     moveCountPruning = false;
     ttCapture = ttMove && pos.capture_or_promotion(ttMove);
 
+    // Mark this node as being searched.
+    ThreadHolding th(thisThread, posKey, ss->ply);
+
     // Step 12. Loop through all pseudo-legal moves until no moves remain
     // or a beta cutoff occurs.
     while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE)
@@ -870,6 +915,12 @@ moves_loop: // When in check, search starts from here
           sync_cout << "info depth " << depth / ONE_PLY
                     << " currmove " << UCI::move(move, pos.is_chess960())
                     << " currmovenumber " << moveCount + thisThread->pvIdx << sync_endl;
+
+      // In MultiPV mode also skip moves which will be searched later as PV moves
+      if (rootNode && std::count(thisThread->rootMoves.begin() + thisThread->pvIdx + 1,
+                                 thisThread->rootMoves.begin() + thisThread->multiPV, move))
+          continue;
+
       if (PvNode)
           (ss+1)->pv = nullptr;
 
@@ -913,10 +964,11 @@ moves_loop: // When in check, search starts from here
           // Multi-cut pruning
           // Our ttMove is assumed to fail high, and now we failed high also on a reduced
           // search without the ttMove. So we assume this expected Cut-node is not singular,
-          // that is multiple moves fail high, and we can prune the whole subtree by returning
-          // the hard beta bound.
-          else if (cutNode && singularBeta > beta)
-              return beta;
+          // that multiple moves fail high, and we can prune the whole subtree by returning
+          // a soft bound.
+          else if (   eval >= beta
+                   && singularBeta >= beta)
+              return singularBeta;
       }
 
       // Check extension (~2 Elo)
@@ -932,7 +984,7 @@ moves_loop: // When in check, search starts from here
       else if (   PvNode
                && pos.rule50_count() > 18
                && depth < 3 * ONE_PLY
-               && ss->ply < 3 * thisThread->rootDepth / ONE_PLY) // To avoid too deep searches
+               && ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4)  // To avoid too many extensions
           extension = ONE_PLY;
 
       // Passed pawn extension
@@ -980,7 +1032,7 @@ moves_loop: // When in check, search starts from here
               if (!pos.see_ge(move, Value(-29 * lmrDepth * lmrDepth)))
                   continue;
           }
-          else if ((!givesCheck || !(pos.blockers_for_king(~us) & from_sq(move)))
+          else if ((!givesCheck || !extension)
                   && !pos.see_ge(move, -PawnValueEg * (depth / ONE_PLY))) // (~20 Elo)
                   continue;
       }
@@ -1012,6 +1064,10 @@ moves_loop: // When in check, search starts from here
       {
           Depth r = reduction(improving, depth, moveCount);
 
+          // Reduction if other threads are searching this position.
+	  if (th.marked())
+              r += ONE_PLY;
+
           // Decrease reduction if position is or has been on the PV
           if (ttPv)
               r -= 2 * ONE_PLY;
@@ -1713,4 +1769,10 @@ void Tablebases::rank_root_moves(Position& pos, Search::RootMoves& rootMoves) {
         if (dtz_available || rootMoves[0].tbScore <= VALUE_DRAW)
             Cardinality = 0;
     }
+    else
+    {
+        // Clean up if root_probe() and root_probe_wdl() have failed
+        for (auto& m : rootMoves)
+            m.tbRank = 0;
+    }
 }