Provides notifications for file changes in a directory.
Invokes client-provided function on every filesystem event in the watched directory. Initially the watched directory is scanned and for every file found, an event is synthesized as if the file was added.
This is not a general purpose directory monitoring tool - list of limitations follows.
Only flat directories with no subdirectories are supported. In case subdirectories are present the behavior is unspecified - events might be passed to Receiver on macOS (due to FSEvents being used) while they probably won't be passed on Linux (due to inotify being used).
Known potential inconsistencies
- For files that are deleted befor the initial scan processed them, clients might receive Removed notification without any prior Added notification.
- Multiple notifications might be produced when a file is added to the watched directory during the initial scan. We are choosing the lesser evil here as the only known alternative strategy would be to invalidate the watcher instance and force user to create a new one whenever filesystem event occurs during the initial scan but that would introduce continuous restarting failure mode (watched directory is not always "owned" by the same process that is consuming it). Since existing clients can handle duplicate events well, we decided for simplicity.
Notifications are provided only for changes done through local user-space filesystem interface. Specifically, it's unspecified if notification would be provided in case of a:
- a file mmap-ed and changed
- a file changed via remote (NFS) or virtual (/proc) FS access to monitored directory
- another filesystem mounted to the watched directory
No support for LLVM VFS.
It is unspecified whether notifications for files being deleted are sent in case the whole watched directory is sent.
Directories containing "too many" files and/or receiving events "too
frequently" are not supported - if the initial scan can't be finished before the watcher instance gets invalidated (see WatcherGotInvalidated) there's no good error handling strategy - the only option for client is to destroy the watcher, restart watching with new instance and hope it won't repeat.
Definition at line 64 of file DirectoryWatcher.h.
