Uncaught Exception: "You need to start the file monitor before watching files" when opening a file

[janbac]

JabRef Version 5.0--2020-03-06--b6d6b79 on Debian GNU/Linux 10 (buster)
(installed from .deb file)

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

What happens:
After a fresh restart jabref works fine. A few days later jabref refuses to open any bib file, producing an error message:
Uncaugh Exception
java.lang.NullPointerException: You need to start the file monitor before watching files

After the next restart jabref works again.

I tracked this down to a restriction in the number of files that inotify can watch concurrently.

If that number is reached on a system, jabref wont open files anymore.

The default on debian is quite low...

Users may recognize this when they use "tail -f" and it says:
tail: inotify cannot be used, reverting to polling: Too many open files

Here is a blog-post that describes the mechanism and the fix
https://medium.com/@ivanermilov/how-to-fix-inotify-cannot-be-used-reverting-to-polling-too-many-open-files-bb1c1437dbf

What should happen:
Jabref should warn me, that it cannot detect changes to my .bib file by other programs
or even also revert to polling as tail does
but open the file anyway

It would be great if the warning would point me to the right solution

Steps to reproduce the behavior:

1. sudo sysctl -w fs.inotify.max_user_watches=1
2. sudo sysctl -w fs.inotify.max_user_instances=1
3. touch aNotExistingFile
4. tail -f aNotExistingFile &
5. start jabref
6. open a bib-file

Full Backtrace

java.lang.NullPointerException: You need to start the file monitor before watching files at java.base/java.util.Objects.requireNonNull(Unknown Source) at org.jabref/org.jabref.gui.util.DefaultFileUpdateMonitor.addListenerForFile(Unknown Source) at org.jabref/org.jabref.gui.collab.DatabaseChangeMonitor.lambda$new$0(Unknown Source) at java.base/java.util.Optional.ifPresent(Unknown Source) at org.jabref/org.jabref.gui.collab.DatabaseChangeMonitor.(Unknown Source) at org.jabref/org.jabref.gui.BasePanel.resetChangeMonitorAndChangePane(Unknown Source) at org.jabref/org.jabref.gui.BasePanel.setupMainPanel(Unknown Source) at org.jabref/org.jabref.gui.BasePanel.(Unknown Source) at org.jabref/org.jabref.gui.importer.actions.OpenDatabaseAction.addNewDatabase(Unknown Source) at org.jabref/org.jabref.gui.importer.actions.OpenDatabaseAction.lambda$openTheFile$1(Unknown Source) at org.jabref/org.jabref.gui.util.DefaultTaskExecutor.lambda$getJavaFXTask$3(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventUtil.fireEvent(Unknown Source) at org.jabref.merged.module/javafx.event.Event.fireEvent(Unknown Source) at org.jabref.merged.module/javafx.concurrent.EventHelper.fireEvent(Unknown Source) at org.jabref.merged.module/javafx.concurrent.Task.fireEvent(Unknown Source) at org.jabref.merged.module/javafx.concurrent.Task.setState(Unknown Source) at org.jabref.merged.module/javafx.concurrent.Task$TaskCallable.lambda$call$1(Unknown Source) at org.jabref.merged.module/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(Unknown Source) at java.base/java.security.AccessController.doPrivileged(Unknown Source) at org.jabref.merged.module/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(Unknown Source) at org.jabref.merged.module/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source) at org.jabref.merged.module/com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method) at org.jabref.merged.module/com.sun.glass.ui.gtk.GtkApplication.lambda$runLoop$11(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source)

[Mebus]

Hallo,

i get the same problem on Fedora Linux 23:

java.lang.NullPointerException: You need to start the file monitor before watching files
	at java.base/java.util.Objects.requireNonNull(Unknown Source)
	at org.jabref/org.jabref.gui.util.DefaultFileUpdateMonitor.addListenerForFile(Unknown Source)
	at org.jabref/org.jabref.gui.collab.DatabaseChangeMonitor.lambda$new$0(Unknown Source)
	at java.base/java.util.Optional.ifPresent(Unknown Source)
	at org.jabref/org.jabref.gui.collab.DatabaseChangeMonitor.<init>(Unknown Source)
	at org.jabref/org.jabref.gui.BasePanel.resetChangeMonitorAndChangePane(Unknown Source)
	at org.jabref/org.jabref.gui.BasePanel.setupMainPanel(Unknown Source)
	at org.jabref/org.jabref.gui.BasePanel.<init>(Unknown Source)
	at org.jabref/org.jabref.gui.importer.actions.OpenDatabaseAction.addNewDatabase(Unknown Source)
	at org.jabref/org.jabref.gui.importer.actions.OpenDatabaseAction.lambda$openTheFile$1(Unknown Source)
	at org.jabref/org.jabref.gui.util.DefaultTaskExecutor.lambda$getJavaFXTask$3(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
	at org.jabref.merged.module/javafx.event.Event.fireEvent(Unknown Source)
	at org.jabref.merged.module/javafx.concurrent.EventHelper.fireEvent(Unknown Source)
	at org.jabref.merged.module/javafx.concurrent.Task.fireEvent(Unknown Source)
	at org.jabref.merged.module/javafx.concurrent.Task.setState(Unknown Source)
	at org.jabref.merged.module/javafx.concurrent.Task$TaskCallable.lambda$call$1(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(Unknown Source)
	at java.base/java.security.AccessController.doPrivileged(Unknown Source)
	at org.jabref.merged.module/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(Unknown Source)
	at org.jabref.merged.module/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
	at org.jabref.merged.module/com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
	at org.jabref.merged.module/com.sun.glass.ui.gtk.GtkApplication.lambda$runLoop$11(Unknown Source)
	at java.base/java.lang.Thread.run(Unknown Source)

My version information is:

JabRef 5.0--2020-03-06--2e6f433
Linux 5.6.15-300.fc32.x86_64 amd64 
Java 13.0.2

Mebus

[Mebus]

Is there a workaround for this?

Mebus

[rezaeimohammad]

I have same problem with Jabref.
It is possible to write clear solution about it?

[Mebus]

Maybe rebooting your systems helps :-P

Mebus

[rezaeimohammad]

Maybe rebooting your systems helps :-P

Mebus
Thanks
Yes, But the rebooting system is the final solution. I have several open application and I can not reboot my system for each time.

[Siedlerchr]

https://docs.jabref.org/faqgeneral#q-unable-to-monitor-file-changes-please-close-files-and-processes-and-restart-you-may-encounter-errors-if-you-continue-with-this-session

[rezaeimohammad]

https://docs.jabref.org/faqgeneral#q-unable-to-monitor-file-changes-please-close-files-and-processes-and-restart-you-may-encounter-errors-if-you-continue-with-this-session

thanks, Now Jabref work perfectly

[Mebus]

I just hit the problem again:

java.lang.NullPointerException: You need to start the file monitor before watching files at java.base/java.util.Objects.requireNonNull(Unknown Source) at org.jabref/org.jabref.gui.util.DefaultFileUpdateMonitor.addListenerForFile(Unknown Source) at org.jabref/org.jabref.gui.collab.DatabaseChangeMonitor.lambda$new$0(Unknown Source) at java.base/java.util.Optional.ifPresent(Unknown Source) at org.jabref/org.jabref.gui.collab.DatabaseChangeMonitor.(Unknown Source) at org.jabref/org.jabref.gui.BasePanel.resetChangeMonitorAndChangePane(Unknown Source) at org.jabref/org.jabref.gui.BasePanel.setupMainPanel(Unknown Source) at org.jabref/org.jabref.gui.BasePanel.(Unknown Source) at org.jabref/org.jabref.gui.importer.actions.OpenDatabaseAction.addNewDatabase(Unknown Source) at org.jabref/org.jabref.gui.importer.actions.OpenDatabaseAction.lambda$openTheFile$1(Unknown Source) at org.jabref/org.jabref.gui.util.DefaultTaskExecutor.lambda$getJavaFXTask$3(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source) at org.jabref.merged.module/com.sun.javafx.event.EventUtil.fireEvent(Unknown Source) at org.jabref.merged.module/javafx.event.Event.fireEvent(Unknown Source) at org.jabref.merged.module/javafx.concurrent.EventHelper.fireEvent(Unknown Source) at org.jabref.merged.module/javafx.concurrent.Task.fireEvent(Unknown Source) at org.jabref.merged.module/javafx.concurrent.Task.setState(Unknown Source) at org.jabref.merged.module/javafx.concurrent.Task$TaskCallable.lambda$call$1(Unknown Source) at org.jabref.merged.module/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(Unknown Source) at java.base/java.security.AccessController.doPrivileged(Unknown Source) at org.jabref.merged.module/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(Unknown Source) at org.jabref.merged.module/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source) at org.jabref.merged.module/com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method) at org.jabref.merged.module/com.sun.glass.ui.gtk.GtkApplication.lambda$runLoop$11(Unknown Source) at java.base/java.lang.Thread.run(Unknown Source)