op-challenger: Remove unused players from memory.

op-challenger/fault/monitor.go

@@ -66,11 +66,13 @@ func (m *gameMonitor) progressGames(ctx context.Context) error {
 	if err != nil {
 		return fmt.Errorf("failed to load games: %w", err)
 	}
+	requiredGames := make(map[common.Address]bool)
 	for _, game := range games {
 		if !m.allowedGame(game.Proxy) {
 			m.logger.Debug("Skipping game not on allow list", "game", game.Proxy)
 			continue
 		}
+		requiredGames[game.Proxy] = true
 		player, err := m.fetchOrCreateGamePlayer(game)
 		if err != nil {
 			m.logger.Error("Error while progressing game", "game", game.Proxy, "err", err)
@@ -78,6 +80,14 @@ func (m *gameMonitor) progressGames(ctx context.Context) error {
 		}
 		player.ProgressGame(ctx)
 	}
+	// Remove the player for any game that's no longer being returned from the list of active games
+	for addr := range m.players {
+		if _, ok := requiredGames[addr]; ok {
+			// Game still required
+			continue
+		}
+		delete(m.players, addr)
+	}
 	return nil
 }
 

op-challenger/fault/monitor_test.go

@@ -77,6 +77,48 @@ func TestMonitorOnlyCreateSpecifiedGame(t *testing.T) {
 	require.Equal(t, 1, games.created[addr2].progressCount)
 }
 
+func TestDeletePlayersWhenNoLongerInListOfGames(t *testing.T) {
+	addr1 := common.Address{0xaa}
+	addr2 := common.Address{0xbb}
+	monitor, source, games := setupMonitorTest(t, nil)
+
+	allGames := []FaultDisputeGame{
+		{
+			Proxy:     addr1,
+			Timestamp: 9999,
+		},
+		{
+			Proxy:     addr2,
+			Timestamp: 9999,
+		},
+	}
+	source.games = allGames
+
+	require.NoError(t, monitor.progressGames(context.Background()))
+	require.Len(t, games.created, 2)
+	require.Contains(t, games.created, addr1)
+	require.Contains(t, games.created, addr2)
+
+	// First game is now old enough it's not returned in the list of active games
+	source.games = source.games[1:]
+	require.NoError(t, monitor.progressGames(context.Background()))
+	require.Len(t, games.created, 2)
+	require.Contains(t, games.created, addr1)
+	require.Contains(t, games.created, addr2)
+
+	// Forget that we created the first game so it can be recreated if needed
+	delete(games.created, addr1)
+
+	// First game now reappears (inexplicably but usefully for our testing)
+	source.games = allGames
+	require.NoError(t, monitor.progressGames(context.Background()))
+	// A new player is created for it because the original was deleted
+	require.Len(t, games.created, 2)
+	require.Contains(t, games.created, addr1)
+	require.Contains(t, games.created, addr2)
+	require.Equal(t, 1, games.created[addr1].progressCount)
+}
+
 func setupMonitorTest(t *testing.T, allowedGames []common.Address) (*gameMonitor, *stubGameSource, *createdGames) {
 	logger := testlog.Logger(t, log.LvlDebug)
 	source := &stubGameSource{}