JabRef dies silently with to few inotify instances

[mkonersmann]

JabRef version 4.3.1 on Ubuntu 18.04

• I have tested the latest development version from http://builds.jabref.org/master/ and the problem persists

When JabRef is started without enough remaining inotify instances, it will die silently (for the user).

Steps to reproduce the behavior:

1. Exit JabRef with a bib file open.
2. In Ubuntu, set the max_inotify_instances too low
   echo 1 > /proc/sys/fs/inotify/max_user_instances
3. Start JabRef
4. JabRef does not start. Only the logs show an error, but not the root cause.

The root cause in my scenario is, that the file cannot be watched by the DefaultFileUpdateMonitor, because there are not enough inotify instances left.
The DefaultFileUpdateMonitorrealizes this, but only logs it on the debug level. As this exception affects user experience, it should be made more prominent.
I will provide a first pull request shortly, which at least logs the exception on the error level. but IMO the user should at least be informed to look at the logs.

Log File

13:39:09.336 [AWT-EventQueue-0] INFO  org.jabref.logic.importer.OpenDatabase - Opening: /home/someuser/references.bib
File: grouptree.fxml not found, attempting with camel case
File: grouptree.css not found, attempting with camel case
13:39:10.718 [AWT-EventQueue-0] ERROR org.jabref.FallbackExceptionHandler - Uncaught exception occurred in Thread[AWT-EventQueue-0,6,main]
java.lang.NullPointerException: null
      at sun.nio.fs.UnixPath.register(UnixPath.java:893) ~[?:1.8.0_201]
      at sun.nio.fs.AbstractPath.register(AbstractPath.java:104) ~[?:1.8.0_201]
      at org.jabref.gui.util.DefaultFileUpdateMonitor.addListenerForFile(DefaultFileUpdateMonitor.java:73) ~[jabref-4.3.1.jar:?]
      at org.jabref.gui.collab.DatabaseChangeMonitor.lambda$new$0(DatabaseChangeMonitor.java:40) ~[jabref-4.3.1.jar:?]
      at java.util.Optional.ifPresent(Optional.java:159) ~[?:1.8.0_201]
      at org.jabref.gui.collab.DatabaseChangeMonitor.<init>(DatabaseChangeMonitor.java:38) ~[jabref-4.3.1.jar:?]
      at org.jabref.gui.BasePanel.<init>(BasePanel.java:241) ~[jabref-4.3.1.jar:?]
      at org.jabref.gui.JabRefFrame.addTab(JabRefFrame.java:1604) ~[jabref-4.3.1.jar:?]
      at org.jabref.gui.JabRefFrame.addParserResult(JabRefFrame.java:1304) ~[jabref-4.3.1.jar:?]
      at org.jabref.JabRefGUI.openWindow(JabRefGUI.java:138) ~[jabref-4.3.1.jar:?]
      at org.jabref.JabRefGUI.<init>(JabRefGUI.java:67) ~[jabref-4.3.1.jar:?]
      at org.jabref.JabRefMain.lambda$start$1(JabRefMain.java:128) ~[jabref-4.3.1.jar:?]
      at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311) ~[?:1.8.0_201]
      at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758) ~[?:1.8.0_201]
      at java.awt.EventQueue.access$500(EventQueue.java:97) ~[?:1.8.0_201]
      at java.awt.EventQueue$3.run(EventQueue.java:709) ~[?:1.8.0_201]
      at java.awt.EventQueue$3.run(EventQueue.java:703) ~[?:1.8.0_201]
      at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_201]
      at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74) ~[?:1.8.0_201]
      at java.awt.EventQueue.dispatchEvent(EventQueue.java:728) ~[?:1.8.0_201]
      at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205) [?:1.8.0_201]
      at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) [?:1.8.0_201]
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) [?:1.8.0_201]
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) [?:1.8.0_201]
      at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) [?:1.8.0_201]
      at java.awt.EventDispatchThread.run(EventDispatchThread.java:82) [?:1.8.0_201]