Watcher prototype » History » Revision 16
Revision 15 (Greg Burri, 08/10/2009 09:52 PM) → Revision 16/17 (Greg Burri, 09/10/2009 01:39 PM)
h1. Watcher prototype
The cache file structure store all the hashes of the shared files. If a file is added or removed from a shared directory (or a subfolder) it should be added or removed from the cache.
As far as I know there is no way to watch changes recursively of a folder tree with Qt. The Qt class _QFileSystemWatcher_ cannot watch recursively.
The only way to synchronize is to periodically scan all the shared data and compare to the cached one. It can be a bit CPU consumer so it should be done with a low priority thread and maybe with a pause between each file hashing.
h2. Native solution
A better solution would be to use native platform API.
h3. Linux : inotify
On Linux it exists a function called "inotify":http://linux.die.net/man/7/inotify
* The big issue is that inotify doesn't support the recursive watch of a directory.
* There is a limitation of the number of watcher, see @/proc/sys/fs/inotify/max_user_watches@, for example : 8192 under Debian.
* There is no problem to create thousands of watcher, it's very light.
/!\ inotify is replaced by fsnotify in the kernel 2.6.31, see : http://lwn.net/Articles/339399/
h3. Windows : ReadDirectoryChangesW and WaitForMultiplesObjects
_ReadDirectoryChangesW_ can watch recursively and asynchronously any change from a given directory. See : http://msdn.microsoft.com/en-us/library/aa365465%28VS.85%29.aspx
Then, a thread can wait an event by calling _WaitForMultiplesObjects_, see : http://msdn.microsoft.com/en-us/library/aa365261%28VS.85%29.aspx
h4. Events when copying :
Beginning of the copy :
<pre>
waitEvent
Action = 1 (FILE_ACTION_ADDED)
filename = "ACDC - Back In Black.mpg"
waitEvent
Action = 3 (FILE_ACTION_MODIFIED)
filename = "ACDC - Back In Black.mpg"
</pre>
End of the copy :
<pre>
waitEvent
Action = 3 (FILE_ACTION_MODIFIED)
filename = "ACDC - Back In Black.mpg"
<pre>