Merge official-stockfish/master

No functional change.

diff --cc src/search.cpp
index 2709092,e3a5a92..a5a64a5
--- 1/src/search.cpp
--- 2/src/search.cpp
+++ b/src/search.cpp
@@@ -252,22 -236,10 +252,16 @@@ void MainThread::search() 
    }
    else
    {
-       for (Thread* th : Threads)
-       {
-           th->bestMoveChanges = 0;
-           if (th != this)
-               th->start_searching();
-       }
- 
-       Thread::search(); // Let's start searching!
+       Threads.start_searching(); // start non-main threads
+       Thread::search();          // main thread start searching
    }
  
 +  if (rootPos.two_boards() && !Threads.abort && Options["Protocol"] == "xboard")
 +  {
 +      while (!Threads.stop && (Partner.sitRequested || Partner.weDead) && Time.elapsed() < Limits.time[us] - 1000)
 +      {}
 +  }
 +
    // When we reach the maximum depth, we can arrive here without a raise of
    // Threads.stop. However, if we are pondering or in an infinite search,
    // the UCI protocol states that we shouldn't print the best move before the
@@@ -291,39 -261,13 +283,13 @@@
    if (Limits.npmsec)
        Time.availableNodes += Limits.inc[us] - Threads.nodes_searched();
  
 -  Thread* bestThread = this;
 +  bestThread = this;
  
-   // Check if there are threads with a better score than main thread
-   if (    int(Options["MultiPV"]) == 1
-       && !Limits.depth
-       && !(Skill(Options["Skill Level"]).enabled() || int(Options["UCI_LimitStrength"]))
-       &&  rootMoves[0].pv[0] != MOVE_NONE)
-   {
-       std::map<Move, int64_t> votes;
-       Value minScore = this->rootMoves[0].score;
- 
-       // Find minimum score
-       for (Thread* th: Threads)
-           minScore = std::min(minScore, th->rootMoves[0].score);
- 
-       // Vote according to score and depth, and select the best thread
-       for (Thread* th : Threads)
-       {
-           votes[th->rootMoves[0].pv[0]] +=
-               (th->rootMoves[0].score - minScore + 14) * int(th->completedDepth);
- 
-           if (abs(bestThread->rootMoves[0].score) >= VALUE_TB_WIN_IN_MAX_PLY)
-           {
-               // Make sure we pick the shortest mate / TB conversion or stave off mate the longest
-               if (th->rootMoves[0].score > bestThread->rootMoves[0].score)
-                   bestThread = th;
-           }
-           else if (   th->rootMoves[0].score >= VALUE_TB_WIN_IN_MAX_PLY
-                    || (   th->rootMoves[0].score > VALUE_TB_LOSS_IN_MAX_PLY
-                        && votes[th->rootMoves[0].pv[0]] > votes[bestThread->rootMoves[0].pv[0]]))
-               bestThread = th;
-       }
-   }
+   if (int(Options["MultiPV"]) == 1 &&
+       !Limits.depth &&
+       !(Skill(Options["Skill Level"]).enabled() || int(Options["UCI_LimitStrength"])) &&
+       rootMoves[0].pv[0] != MOVE_NONE)
+       bestThread = Threads.get_best_thread();
  
    bestPreviousScore = bestThread->rootMoves[0].score;
  

diff --cc src/thread.cpp
index d96e922,a27a60c..4be8245
--- 1/src/thread.cpp
--- 2/src/thread.cpp
+++ b/src/thread.cpp
@@@ -208,10 -208,10 +208,10 @@@ void ThreadPool::start_thinking(Positio
  
    for (Thread* th : *this)
    {
-       th->nodes = th->tbHits = th->nmpMinPly = 0;
+       th->nodes = th->tbHits = th->nmpMinPly = th->bestMoveChanges = 0;
        th->rootDepth = th->completedDepth = 0;
        th->rootMoves = rootMoves;
 -      th->rootPos.set(pos.fen(), pos.is_chess960(), &setupStates->back(), th);
 +      th->rootPos.set(pos.variant(), pos.fen(), pos.is_chess960(), &setupStates->back(), th);
    }
  
    setupStates->back() = tmp;

diff --cc src/thread.h
index 6a73f33,a69e1d1..cd141cf
--- 1/src/thread.h
--- 2/src/thread.h
+++ b/src/thread.h
@@@ -110,13 -109,15 +110,16 @@@ struct ThreadPool : public std::vector<
    MainThread* main()        const { return static_cast<MainThread*>(front()); }
    uint64_t nodes_searched() const { return accumulate(&Thread::nodes); }
    uint64_t tb_hits()        const { return accumulate(&Thread::tbHits); }
+   Thread* get_best_thread() const;
+   void start_searching();
+   void wait_for_search_finished() const;
  
    std::atomic_bool stop, increaseDepth;
 +  std::atomic_bool abort, sit;
  
 -private:
    StateListPtr setupStates;
  
 +private:
    uint64_t accumulate(std::atomic<uint64_t> Thread::* member) const {
  
      uint64_t sum = 0;