Remove race condition in clock switching

[xboard.git] / backend.c

diff --git a/backend.c b/backend.c
index 42f434e..8f77f6b 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -190,7 +190,7 @@ void ParseGameHistory P((char *game));
 void ParseBoard12 P((char *string));
 void KeepAlive P((void));
 void StartClocks P((void));
-void SwitchClocks P((void));
+void SwitchClocks P((int nr));
 void StopClocks P((void));
 void ResetClocks P((void));
 char *PGNDate P((void));
@@ -3318,10 +3318,10 @@ read_from_ics(isr, closure, data, count, error)
                    looking_at(buf, &i, "It is not your move")) {
                    /* Illegal move */
                    if (ics_user_moved && forwardMostMove > backwardMostMove) { // only backup if we already moved
-                       currentMove = --forwardMostMove;
+                       currentMove = forwardMostMove-1;
                        DisplayMove(currentMove - 1); /* before DMError */
                        DrawPosition(FALSE, boards[currentMove]);
-                       SwitchClocks();
+                       SwitchClocks(forwardMostMove-1); // [HGM] race
                        DisplayBothClocks();
                    }
                    DisplayMoveError(_("Illegal move (rejected by ICS)")); // [HGM] but always relay error msg
@@ -7287,9 +7287,9 @@ if(appData.debugMode) fprintf(debugFP, "nodes = %d, %lld\n", (int) programStats.
            gameMode = EditGame;
            ModeHighlight();
        }
-       currentMove = --forwardMostMove;
+       currentMove = forwardMostMove-1;
        DisplayMove(currentMove-1); /* before DisplayMoveError */
-       SwitchClocks();
+       SwitchClocks(forwardMostMove-1); // [HGM] race
        DisplayBothClocks();
        sprintf(buf1, _("Illegal move \"%s\" (rejected by %s chess program)"),
                parseList[currentMove], cps->which);
@@ -8362,8 +8362,8 @@ MakeMove(fromX, fromY, toX, toY, promoChar)
     }
     CopyBoard(boards[forwardMostMove+1], boards[forwardMostMove]);
     ApplyMove(fromX, fromY, toX, toY, promoChar, boards[forwardMostMove+1]);
-    forwardMostMove++; // [HGM] bare: moved to after ApplyMove, to make sure clock interrupt finds complete board
-    SwitchClocks(); // uses forwardMostMove, so must be done after incrementing it !
+    // forwardMostMove++; // [HGM] bare: moved to after ApplyMove, to make sure clock interrupt finds complete board
+    SwitchClocks(forwardMostMove+1); // [HGM] race: incrementing move nr inside
     timeRemaining[0][forwardMostMove] = whiteTimeRemaining;
     timeRemaining[1][forwardMostMove] = blackTimeRemaining;
     gameInfo.result = GameUnfinished;
@@ -14032,7 +14032,7 @@ DecrementClocks()
    from the color that is *not* on move now.
 */
 void
-SwitchClocks()
+SwitchClocks(int newMoveNr)
 {
     long lastTickLength;
     TimeMark now;
@@ -14042,7 +14042,7 @@ SwitchClocks()
 
     if (StopClockTimer() && appData.clockMode) {
        lastTickLength = SubtractTimeMarks(&now, &tickStartTM);
-       if (WhiteOnMove(forwardMostMove)) {
+       if (!WhiteOnMove(forwardMostMove)) {
            if(blackNPS >= 0) lastTickLength = 0;
            blackTimeRemaining -= lastTickLength;
            /* [HGM] PGNtime: save time for PGN file if engine did not give it */
@@ -14059,6 +14059,7 @@ SwitchClocks()
        }
        flagged = CheckFlags();
     }
+    forwardMostMove = newMoveNr; // [HGM] race: change stm when no timer interrupt scheduled
     CheckTimeControl();
 
     if (flagged || !appData.clockMode) return;