Fix a (theoretical) race leading to a crash

[stockfish] / src / search.cpp

diff --git a/src/search.cpp b/src/search.cpp
index b8ac4ab3cd2940e13d3890effdddc69e4f0e4a45..eaba6c6d83b96fee4797696a6c606c3648bddfe6 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -332,7 +332,7 @@ finalize:
   // but if we are pondering or in infinite search, we shouldn't print the best
   // move before we are told to do so.
   if (!Signals.stop && (Limits.ponder || Limits.infinite))
-      Threads[pos.thread()].wait_for_stop_or_ponderhit();
+      Threads.this_thread()->wait_for_stop_or_ponderhit();
 
   // Best move could be MOVE_NONE when searching on a stalemate position
   cout << "bestmove " << move_to_uci(RootMoves[0].pv[0], Chess960)
@@ -530,7 +530,6 @@ namespace {
     assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
     assert((alpha == beta - 1) || PvNode);
     assert(depth > DEPTH_ZERO);
-    assert(pos.thread() >= 0 && pos.thread() < Threads.size());
 
     Move movesSearched[MAX_MOVES];
     StateInfo st;
@@ -544,7 +543,7 @@ namespace {
     bool isPvMove, inCheck, singularExtensionNode, givesCheck;
     bool captureOrPromotion, dangerous, doFullDepthSearch;
     int moveCount = 0, playedMoveCount = 0;
-    Thread& thread = Threads[pos.thread()];
+    Thread* thisThread = Threads.this_thread();
     SplitPoint* sp = NULL;
 
     refinedValue = bestValue = value = -VALUE_INFINITE;
@@ -553,8 +552,8 @@ namespace {
     ss->ply = (ss-1)->ply + 1;
 
     // Used to send selDepth info to GUI
-    if (PvNode && thread.maxPly < ss->ply)
-        thread.maxPly = ss->ply;
+    if (PvNode && thisThread->maxPly < ss->ply)
+        thisThread->maxPly = ss->ply;
 
     // Step 1. Initialize node
     if (SpNode)
@@ -670,7 +669,7 @@ namespace {
         &&  refinedValue + razor_margin(depth) < beta
         &&  ttMove == MOVE_NONE
         &&  abs(beta) < VALUE_MATE_IN_MAX_PLY
-        && !pos.has_pawn_on_7th(pos.side_to_move()))
+        && !pos.pawn_on_7th(pos.side_to_move()))
     {
         Value rbeta = beta - razor_margin(depth);
         Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, DEPTH_ZERO);
@@ -817,7 +816,7 @@ split_point_start: // At split points actual search starts from here
     // Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
     while (   bestValue < beta
            && (move = mp.next_move()) != MOVE_NONE
-           && !thread.cutoff_occurred()
+           && !thisThread->cutoff_occurred()
            && !Signals.stop)
     {
       assert(is_ok(move));
@@ -847,7 +846,7 @@ split_point_start: // At split points actual search starts from here
       {
           Signals.firstRootMove = (moveCount == 1);
 
-          if (pos.thread() == 0 && SearchTime.elapsed() > 2000)
+          if (thisThread == Threads.main_thread() && SearchTime.elapsed() > 2000)
               cout << "info depth " << depth / ONE_PLY
                    << " currmove " << move_to_uci(move, Chess960)
                    << " currmovenumber " << moveCount + PVIdx << endl;
@@ -1039,7 +1038,7 @@ split_point_start: // At split points actual search starts from here
               && value < beta) // We want always alpha < beta
               alpha = value;
 
-          if (SpNode && !thread.cutoff_occurred())
+          if (SpNode && !thisThread->cutoff_occurred())
           {
               sp->bestValue = value;
               sp->bestMove = move;
@@ -1054,9 +1053,9 @@ split_point_start: // At split points actual search starts from here
       if (   !SpNode
           && depth >= Threads.min_split_depth()
           && bestValue < beta
-          && Threads.available_slave_exists(pos.thread())
+          && Threads.available_slave_exists(thisThread)
           && !Signals.stop
-          && !thread.cutoff_occurred())
+          && !thisThread->cutoff_occurred())
           bestValue = Threads.split<FakeSplit>(pos, ss, alpha, beta, bestValue, &bestMove,
                                                depth, threatMove, moveCount, &mp, NT);
     }
@@ -1080,7 +1079,7 @@ split_point_start: // At split points actual search starts from here
 
     // Step 21. Update tables
     // Update transposition table entry, killers and history
-    if (!SpNode && !Signals.stop && !thread.cutoff_occurred())
+    if (!SpNode && !Signals.stop && !thisThread->cutoff_occurred())
     {
         move = bestValue <= oldAlpha ? MOVE_NONE : bestMove;
         bt   = bestValue <= oldAlpha ? BOUND_UPPER
@@ -1131,7 +1130,6 @@ split_point_start: // At split points actual search starts from here
     assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
     assert((alpha == beta - 1) || PvNode);
     assert(depth <= DEPTH_ZERO);
-    assert(pos.thread() >= 0 && pos.thread() < Threads.size());
 
     StateInfo st;
     Move ttMove, move, bestMove;
@@ -1827,8 +1825,7 @@ void Thread::idle_loop(SplitPoint* sp_master) {
           lock_release(Threads.splitLock);
 
           Stack ss[MAX_PLY_PLUS_2];
-          Position pos(*sp->pos, threadID);
-          int master = sp->master;
+          Position pos(*sp->pos);
 
           memcpy(ss, sp->ss - 1, 4 * sizeof(Stack));
           (ss+1)->sp = sp;
@@ -1847,20 +1844,21 @@ void Thread::idle_loop(SplitPoint* sp_master) {
           assert(is_searching);
 
           is_searching = false;
-          sp->slavesMask &= ~(1ULL << threadID);
+          sp->slavesMask &= ~(1ULL << idx);
           sp->nodes += pos.nodes_searched();
 
-          // After releasing the lock we cannot access anymore any SplitPoint
-          // related data in a reliably way becuase it could have been released
-          // under our feet by the sp master.
-          lock_release(sp->lock);
-
           // Wake up master thread so to allow it to return from the idle loop in
           // case we are the last slave of the split point.
           if (   Threads.use_sleeping_threads()
-              && threadID != master
-              && !Threads[master].is_searching)
-              Threads[master].wake_up();
+              && this != sp->master
+              && !sp->master->is_searching)
+              sp->master->wake_up();
+
+          // After releasing the lock we cannot access anymore any SplitPoint
+          // related data in a safe way becuase it could have been released under
+          // our feet by the sp master. Also accessing other Thread objects is
+          // unsafe because if we are exiting there is a chance are already freed.
+          lock_release(sp->lock);
       }
   }
 }