WatchService

The WatchService in Java uses different mechanisms depending on the operating system. On macOS, the WatchService implementation generally relies on polling rather than true event-based notifications.

Why does WatchService use polling on macOS?

1. Native Limitations: The Java NIO WatchService was designed with Windows' ReadDirectoryChangesW and Linux's inotify in mind, both of which provide efficient event-based file change notifications. macOS does not have a direct equivalent in its POSIX-compliant API.
2. Polling Implementation: As a result, the implementation on macOS often falls back to a polling mechanism, where it periodically checks for changes in the directory's metadata (like timestamps or file lists).

Implications of Polling

• Performance: Polling is less efficient than event-based mechanisms because it consumes more CPU resources, especially for directories with many files.
• Latency: Polling introduces a delay in detecting changes, which depends on the polling interval.

Alternatives for Event-Based File Watching on macOS

If you need a more efficient and event-driven approach, consider using native tools or libraries that wrap macOS's FSEvents or kqueue APIs:

1. Third-Party Libraries:
   • JNotify: Provides a cross-platform wrapper for native file system events.
   • Watchdog: Cross-platform file watching tool in Go with better macOS support.
2. Native Integration: Use FSEvents or kqueue directly through JNI or with a library like JNA.

For robust file watching on macOS, leveraging native tools or libraries tailored to the platform can avoid the inefficiencies of Java's default WatchService implementation.