FSEvents

FSEvents is a macOS framework that provides a low-level, asynchronous mechanism for applications to receive notifications about changes to the file system. It allows applications to monitor specific directories or the entire file system for modifications such as file creation, deletion, modification, renaming, and attribute changes.

The FSEvents API uses an event-driven model. Instead of constantly polling the file system for changes (which is resource-intensive), applications register paths of interest with the FSEvents service. The FSEvents service then monitors these paths and notifies the application only when changes occur. This approach is significantly more efficient than polling.

Key characteristics of FSEvents include:

• Asynchronous: Notifications are delivered to the application asynchronously, allowing the application to continue processing other tasks without being blocked while waiting for file system events.
• Low-Level: It provides a direct interface to the kernel's file system event monitoring system.
• Directory-Based Monitoring: Applications monitor entire directories, not individual files. Changes within subdirectories are also reported.
• Event Streams: Changes are reported as a stream of events, often providing a batch of changes that have occurred since the last notification.
• Persistent Event Tracking: FSEvents can track changes even when the application is not running, allowing the application to catch up on events that occurred while it was inactive. The specific duration for which events are stored depends on system resources and configuration.
• Uses Kernel Support: FSEvents leverages kernel-level functionality, making it fast and efficient.

FSEvents is used by a wide variety of applications, including:

• File synchronization applications: To detect changes that need to be synchronized.
• Backup applications: To identify files that need to be backed up.
• Code editors and IDEs: To automatically update project files when changes are made outside the editor.
• Indexing services: To maintain an up-to-date index of files on the system.
• System monitoring tools: To track changes to system files and directories.

Alternatives to FSEvents on other operating systems include similar system-level file monitoring APIs, such as inotify on Linux and ReadDirectoryChangesW on Windows. These APIs provide similar functionality but are specific to their respective operating systems. While cross-platform libraries exist to abstract over these differences, they typically expose a higher-level interface than FSEvents and might not offer the same level of performance or control.