Retire slavesPositions

Save the current active position in each Thread
instead of keeping a centralized array in struct
SplitPoint.

This allow to skip a memset() call at each split.

No functional change.

src/search.cpp

@@ -1672,9 +1672,9 @@ void Thread::idle_loop() {
 
           sp->mutex.lock();
 
-          assert(sp->slavesPositions[idx] == NULL);
+          assert(activePosition == NULL);
 
-          sp->slavesPositions[idx] = &pos;
+          activePosition = &pos;
 
           switch (sp->nodeType) {
           case Root:
@@ -1693,7 +1693,7 @@ void Thread::idle_loop() {
           assert(searching);
 
           searching = false;
-          sp->slavesPositions[idx] = NULL;
+          activePosition = NULL;
           sp->slavesMask &= ~(1ULL << idx);
           sp->nodes += pos.nodes_searched();
 
@@ -1742,7 +1742,7 @@ void check_time() {
       nodes = RootPos.nodes_searched();
 
       // Loop across all split points and sum accumulated SplitPoint nodes plus
-      // all the currently active slaves positions.
+      // all the currently active positions nodes.
       for (size_t i = 0; i < Threads.size(); i++)
           for (int j = 0; j < Threads[i]->splitPointsSize; j++)
           {
@@ -1754,8 +1754,9 @@ void check_time() {
               Bitboard sm = sp.slavesMask;
               while (sm)
               {
-                  Position* pos = sp.slavesPositions[pop_lsb(&sm)];
-                  nodes += pos ? pos->nodes_searched() : 0;
+                  Position* pos = Threads[pop_lsb(&sm)]->activePosition;
+                  if (pos)
+                      nodes += pos->nodes_searched();
               }
 
               sp.mutex.unlock();

src/thread.cpp

@@ -19,7 +19,6 @@
 
 #include <algorithm> // For std::count
 #include <cassert>
-#include <cstring> // For memset
 #include <iostream>
 
 #include "movegen.h"
@@ -49,6 +48,7 @@ Thread::Thread() /* : splitPoints() */ { // Value-initialization bug in MSVC
   searching = exit = false;
   maxPly = splitPointsSize = 0;
   activeSplitPoint = NULL;
+  activePosition = NULL;
   idx = Threads.size();
 
   if (!thread_create(handle, start_routine, this))
@@ -281,8 +281,6 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
   sp.cutoff = false;
   sp.ss = ss;
 
-  memset(sp.slavesPositions, 0, sizeof(sp.slavesPositions));
-
   // Try to allocate available threads and ask them to start searching setting
   // 'searching' flag. This must be done under lock protection to avoid concurrent
   // allocation of the same slave by another master.
@@ -291,6 +289,7 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
 
   splitPointsSize++;
   activeSplitPoint = &sp;
+  activePosition = NULL;
 
   size_t slavesCnt = 1; // This thread is always included
   Thread* slave;
@@ -318,6 +317,7 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
       // In helpful master concept a master can help only a sub-tree of its split
       // point, and because here is all finished is not possible master is booked.
       assert(!searching);
+      assert(!activePosition);
   }
 
   // We have returned from the idle loop, which means that all threads are
@@ -329,6 +329,7 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
   searching = true;
   splitPointsSize--;
   activeSplitPoint = sp.parentSplitPoint;
+  activePosition = &pos;
   pos.set_nodes_searched(pos.nodes_searched() + sp.nodes);
   *bestMove = sp.bestMove;
   *bestValue = sp.bestValue;

src/thread.h

@@ -75,7 +75,6 @@ struct SplitPoint {
 
   // Shared data
   Mutex mutex;
-  Position* slavesPositions[MAX_THREADS];
   volatile uint64_t slavesMask;
   volatile int64_t nodes;
   volatile Value alpha;
@@ -110,6 +109,7 @@ struct Thread {
   Material::Table materialTable;
   Endgames endgames;
   Pawns::Table pawnsTable;
+  Position* activePosition;
   size_t idx;
   int maxPly;
   Mutex mutex;