Prefer pause mode on pondering engine over 'easy'

If the thinking engine is stopped after its move because it does not
support pause, is is still better to use pause on the pondering engine
than to switch of its pondering with 'easy', as the latter might not
be instantaneous. Also switch off pondering in the thinking engine before
it gives the move, just in case it does not respond immediately to
easy / hard.

diff --git a/backend.c b/backend.c
index 614f725..d78319a 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -224,6 +224,7 @@ FILE *WriteTourneyFile P((char *results, FILE *f));
 void DisplayTwoMachinesTitle P(());
 static void ExcludeClick P((int index));
 void ToggleSecond P((void));
+void PauseEngine P((ChessProgramState *cps));
 
 #ifdef WIN32
        extern void ConsoleCreate();
@@ -8111,9 +8112,13 @@ FakeBookMove: // [HGM] book: we jump here to simulate machine moves after book h
            if(appData.debugMode) fprintf(debugFP, "pause %s engine after move\n", cps->which);
            safeStrCpy(stashedInputMove, message, MSG_SIZ);
            stalledEngine = cps;
-           if(appData.ponderNextMove) { // bring both engines out of ponder
-               SendToProgram("easy\n", &first);
-               if(gameMode == TwoMachinesPlay) SendToProgram("easy\n", &second);
+           if(appData.ponderNextMove) { // bring opponent out of ponder
+               if(gameMode == TwoMachinesPlay) {
+                   if(cps->other->pause)
+                       PauseEngine(cps->other);
+                   else
+                       SendToProgram("easy\n", cps->other);
+               }
            }
            StopClocks();
            return;
@@ -13402,7 +13407,7 @@ PauseEvent ()
        if(stalledEngine) { // [HGM] pause: resume game by releasing withheld move
            StartClocks();
            if(gameMode == TwoMachinesPlay) { // we might have to make the opponent resume pondering
-               if(stalledEngine->other->pause) UnPauseEngine(stalledEngine->other);
+               if(stalledEngine->other->pause == 2) UnPauseEngine(stalledEngine->other);
                else if(appData.ponderNextMove) SendToProgram("hard\n", stalledEngine->other);
            }
            if(appData.ponderNextMove) SendToProgram("hard\n", stalledEngine);
@@ -13468,16 +13473,16 @@ PauseEvent ()
                    else
                        SendToProgram("easy\n", onMove->other);
                    StopClocks();
-               }
+               } else if(appData.ponderNextMove) SendToProgram("easy\n", onMove); // pre-emptively bring out of ponder
            } else if(gameMode == (WhiteOnMove(forwardMostMove) ? MachinePlaysWhite : MachinePlaysBlack)) { // engine on move
                if(first.pause) {
                    PauseEngine(&first);
                    StopClocks();
-               }
+               } else if(appData.ponderNextMove) SendToProgram("easy\n", &first); // pre-emptively bring out of ponder
            } else { // human on move, pause pondering by either method
                if(first.pause) 
                    PauseEngine(&first);
-               else
+               else if(appData.ponderNextMove) 
                    SendToProgram("easy\n", &first);
                StopClocks();
            }