I'm using IcePush with Vaadin and this addon https://vaadin.com/directory#addon/icepush

For some reason Icepush occasionally throws java.lang.NegativeArraySizeException and stops working:

Caused by: java.lang.NegativeArraySizeException
         at java.util.AbstractCollection.toArray(AbstractCollection.java:119)
         at java.util.ArrayList.<init>(ArrayList.java:131)
         at org.icepush.servlet.BrowserDispatcher.discardUnusedServlets(BrowserDispatcher.java:89)
         at org.icepush.servlet.BrowserDispatcher.service(BrowserDispatcher.java:47)
         at org.icepush.servlet.PathDispatcher.service(PathDispatcher.java:45)
         at org.icepush.servlet.MainServlet.service(MainServlet.java:71)
         ... 38 more

When looking at the implementation of BrowserDispatcher.discardUnusedServlets()-method it seems like there has been two concurrent threads accessing this method and somehow managed to call BrowserDispatcher.BrowserEntry.discardIfExpired()-> browserBoundServlets.remove(id) in a way that makes browserBoundServlets.values().size() return value less than zero.

By making browserBoundServlets map thread-safe or synchronizing related method accesses, could make this bug go away.