title: QFileSystemWatcher - does it need to run in another thread?
body: <p>I have a class that does some parsing of two large (~90K rows, 11 columns in the first and around ~20K, 5 columns in the second) CSV files. According to the specification I'm working with the CSV files can be externally changed (removing/adding of new rows; columns remain constant as well as the paths). Such updates can happen at any time (though highly unlikely that an update will be launched in time intervals shorter than a couple of minutes) and an update of any of the two files has to terminate the current processing of all that data (CSV, XML from an HTTP GET request, UDP telegrams), followed by re-parsing the content of each of the two (or just one if only one has changed).</p>
  
  <p>I keep the CSV data (quite reduced since I apply multiple filters to remove unwanted entries) in memory to speed working with it and also to avoid unnecessary IO operations (opening, reading, closing file).</p>
  
  <p>Right now I'm looking into the <a href="http://doc.qt.io/qt-5/qfilesystemwatcher.html" rel="nofollow noreferrer">QFileSystemWatcher</a>, which seems to be exactly what I need. However I'm unable to find any information on how it actually works internally.</p>
  
  <p>Since all I need is to monitor 2 files for changes the number of files shouldn't be an issue. Do I need to run it in a separate thread (since the watcher is part of the same class where the CSV parsing happens) or is it safe to say that it can run without too much fuss (that is it works asynchronously like the <code>QNetworkAccessManager</code>)? My dev environment for now is a 64bit Ubuntu VM (VirtualBox) on a relatively powerful host (a HP Z240 workstation) however the target system is an embedded one. While the whole parsing of the CSV files takes just 2-3 seconds at the most I don't know how much performance impact there will be once the application gets deployed so additional overhead is something of a concern of mine.</p>