Fix concurrency in Swiss tourneys

The pairing engine was consulted for the next round before all games of
the previous round were finished, if other XBoard instances were still
playing games. This caused the instances finishing early to stall
indefinitely. This is fixed by moving the Swiss pairing code to after
the syncInterval code. The normal pairing code (the call to Pairing)
must stay before it, because it determines the syncInterval. So ther is
a bit of tourneyType dependence cluttering up the code here. :-(

diff --git a/backend.c b/backend.c
index 6238eeb..6243fa3 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -9779,22 +9779,7 @@ NextTourneyGame(int nr, int *swapColors)
     InitTimeControls(); // TC might be altered from tourney file
 
     nPlayers = CountPlayers(appData.participants); // count participants
-    if(appData.tourneyType < 0 && appData.pairingEngine[0]) {
-       if(nr>=0 && !pairingReceived) {
-           char buf[1<<16];
-           if(pairing.pr == NoProc) StartChessProgram(&pairing);
-           snprintf(buf, 1<<16, "results %d %s\n", nPlayers, appData.results);
-           SendToProgram(buf, &pairing);
-           snprintf(buf, 1<<16, "pairing %d\n", nr+1);
-           SendToProgram(buf, &pairing);
-           return 0; // wait for pairing engine to answer (which causes NextTourneyGame to be called again...
-       }
-       pairingReceived = 0;                              // ... so we continue here 
-       syncInterval = nPlayers/2; *swapColors = 0;
-       appData.matchGames = appData.tourneyCycles * syncInterval - 1;
-       whitePlayer = savedWhitePlayer-1; blackPlayer = savedBlackPlayer-1;
-       matchGame = 1; roundNr = nr / syncInterval + 1;
-    } else
+    if(appData.tourneyType < 0) syncInterval = nPlayers/2; else
     *swapColors = Pairing(nr<0 ? 0 : nr, nPlayers, &whitePlayer, &blackPlayer, &syncInterval);
 
     if(syncInterval) {
@@ -9809,6 +9794,29 @@ NextTourneyGame(int nr, int *swapColors)
        waitingForGame = FALSE;
     }
 
+    if(appData.tourneyType < 0) {
+       if(nr>=0 && !pairingReceived) {
+           char buf[1<<16];
+           if(pairing.pr == NoProc) {
+               if(!appData.pairingEngine[0]) {
+                   DisplayFatalError(_("No pairing engine specified"), 0, 1);
+                   return 0;
+               }
+               StartChessProgram(&pairing); // starts the pairing engine
+           }
+           snprintf(buf, 1<<16, "results %d %s\n", nPlayers, appData.results);
+           SendToProgram(buf, &pairing);
+           snprintf(buf, 1<<16, "pairing %d\n", nr+1);
+           SendToProgram(buf, &pairing);
+           return 0; // wait for pairing engine to answer (which causes NextTourneyGame to be called again...
+       }
+       pairingReceived = 0;                              // ... so we continue here 
+       *swapColors = 0;
+       appData.matchGames = appData.tourneyCycles * syncInterval - 1;
+       whitePlayer = savedWhitePlayer-1; blackPlayer = savedBlackPlayer-1;
+       matchGame = 1; roundNr = nr / syncInterval + 1;
+    }
+
     if(first.pr != NoProc) return 1; // engines already loaded
 
     // redefine engines, engine dir, etc.