ConcurrentModificationException when logging that a game is starting

[ajanata]

Mar 01, 2018 10:03:18 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [net.socialgamer.cah.servlets.AjaxServlet] in context with path [/zy] threw exception
java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextNode(HashMap.java:1442)
        at java.util.HashMap$KeyIterator.next(HashMap.java:1466)
        at java.util.AbstractCollection.toString(AbstractCollection.java:461)
        at java.util.Formatter$FormatSpecifier.printString(Formatter.java:2886)
        at java.util.Formatter$FormatSpecifier.print(Formatter.java:2763)
        at java.util.Formatter.format(Formatter.java:2520)
        at java.util.Formatter.format(Formatter.java:2455)
        at java.lang.String.format(String.java:2940)
        at net.socialgamer.cah.data.Game.start(Game.java:685)
        at net.socialgamer.cah.handlers.StartGameHandler.handleWithUserInGame(StartGameHandler.java:83)
        at net.socialgamer.cah.handlers.GameWithPlayerHandler.handle(GameWithPlayerHandler.java:57)
        at net.socialgamer.cah.handlers.GameHandler.handle(GameHandler.java:77)
        at net.socialgamer.cah.servlets.AjaxServlet.handleRequest(AjaxServlet.java:96)
        at net.socialgamer.cah.servlets.CahServlet.doPost(CahServlet.java:116)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at net.socialgamer.cah.CacheControlFilter.doFilter(CacheControlFilter.java:31)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:221)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:436)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)

This is at:

        logger.info(String.format("Starting game %d with card sets %s, Cardcast %s, %d blanks, %d "
            + "max players, %d max spectators, %d score limit, players %s, unique %s.",
            id, options.cardSetIds, cardcastDeckIds, options.blanksInDeck, options.playerLimit,
            options.spectatorLimit, options.scoreGoal, players, currentUniqueId));

So one of those Sets is being modified concurrently. Possibly need to synchronize on all of them? Ugh.