java/nio/file/WatchService/UpdateInterference.java test creates a couple of daemon threads which have an infinite loop inside. When the test finishes, those daemon still keep running as long as jtreg use this instance of JVM to run other tests (the test doesn't run in othervm mode).

The test also creates a WatchService which creates a "FileSystemWatchService" daemon thread. Then, the test doesn't close this WatchService, and as a result, this daemon thread keeps running as well.

The test shouldn't leave daemon threads when it finishes. It may slow down further test execution. If other tests also leave daemon threads, it may cause intermittent test failures, see for example JDK-8160642 and JDK-8162757.