Monitoring a directory for new file creation without FileSystemWatcher

Question

I have to create a Windows service which monitors a specified folder for new files and processes it and moves it to other location.

I started with using FileSyste

Answer 1

Yes, you can create a Timer, and plug a handler into the Elapsed event that will instantiate a DirectoryInfo class for the directory you're watching, and call either GetFiles() or EnumerateFiles(). GetFiles() returns a FileInfo[] array, while EnumerateFiles() returns a "streaming" IEnumerable. EnumerateFiles() will be more efficient if you expect a lot of files to be in that folder when you look; you can start working with the IEnumerable before the method has retrieved all the FileInfos, while GetFiles will make you wait.

As to why this may actually be better than FileWatcher, it depends on the architecture behind the scenes. Take, for example, a basic Extract/Transform/Validate/Load workflow. First, such a workflow may have to create expensive instances of objects (DB connections, instances of a rules engine, etc). This one-time overhead is significantly mitigated if the workflow is structured to handle everything available to it in one go. Second, FileWatcher would require anything called by the event handlers, like this workflow, to be thread-safe, since MANY events can be running at once if files are constantly flowing in. If that is not feasible, a Timer can be very easily configured to restrict the system to one running workflow, by having event handlers examine a thread-safe "process running" flag and simply terminate if another handler thread has set it and not yet finished. The files in the folder at that time will be picked up the next time the Timer fires, unlike FileWatcher, where if you terminate the handler the information about the existence of that file is lost.