Is Java 7 WatchService Slow for Anyone Else?

Question

WatchService looks like a great technology but its been too slow to be useful on the OS X and Linux systems I've tested on. To add insult to injury, it doesn't seem to get notified of all events either.

This is the case both with my own code and the canonical example from Oracle. (http://docs.oracle.com/javase/tutorial/displayCode.html?code=http://docs.oracle.com/javase/tutorial/essential/io/examples/WatchDir.java)

I recognize that the OS X OpenJDK port is unsure of this functionality (see https://wikis.oracle.com/display/OpenJDK/Mac+OS+X+Port+Project+Status)

Has anyone been using this in production with success?

Answer 1

I have much better response times if I change

folder.register(watcher, StandardWatchEventKinds.ENTRY_MODIFY);

to

folder.register(watcher, new WatchEvent.Kind[]{StandardWatchEventKinds.ENTRY_MODIFY}, SensitivityWatchEventModifier.HIGH);

Answer 2

JDK 7 does not yet have a native implementation of WatchService for MacOS. Rather than listening for native file system events, it uses the fallback sun.nio.fs.PollingWatchService, which periodically traverses the file system and checks the last modified timestamp of each file and subdirectory in the tree. I've also found it to be unusably slow.

There is a native implementation of WatchService for Mac:

http://code.google.com/p/barbarywatchservice/

I haven't tried to use it myself.