What's the best practice to recover from a FileSystemWatcher error?

Question

After a FileSystemWatcher.Error event was raised, I have no clue about what to do next. The exception can be a [relatively] minor one, such as

too many changes at once in directory

which doesn't affect the watcher's watching process, but it can also be a big issue - such as the watched directory being deleted, in which case the watcher is no longer functional.

My question is what is the best way to handle the Error event?

Stop using the FileSystemWatcher, it's unreliable write a polling service. — saj, Jul 26 '12 at 10:11
I'm using a modified FileSystemWatcher which solves most of the reliability issues of the original watcher [overflow issues, duplicated events and network-path watching] — Nissim, Jul 26 '12 at 10:14
Or check for files on an event that happens before it's painted & displayed on the screen. Works well for context menu's. (edit: Sounds nice Nissim, share? :P) — negligible, Jul 26 '12 at 10:19
I intend to share it, once i'm done closing all the edges. i'll keep you posted — Nissim, Jul 26 '12 at 11:08

score 3 · Answer 1 · answered Jul 26 '12 at 10:13

Depends on the error surely?

If it is too much data because the buffer was overrun (many changes) do a list directory and grab the changes you're after.
If it is too much data because you're not processing the FileSystemWatcher events quickly enough, ensure you're processing it efficiently.
Deleted directory, can't do anything about it other than disposing the FileSystemWatcher, or maybe watching the parent for a recreation of that directory name again.

score 1 · Answer 2 · answered Jul 26 '12 at 10:12

I would simply get the inner exception type, then decide on a per-error basis what to do ( restart or fail ).

So

myWatcher.Error += new ErrorEventHandler(OnError);

Followde by

private static void OnError(object source, ErrorEventArgs e)
{
    if (e.GetException().GetType() == typeof(InternalBufferOverflowException))
    {
        //  This can happen if Windows is reporting many file system events quickly 
        //  and internal buffer of the  FileSystemWatcher is not large enough to handle this
        //  rate of events. The InternalBufferOverflowException error informs the application
        //  that some of the file system events are being lost.
        Console.WriteLine(("The file system watcher experienced an internal buffer overflow: " + e.GetException().Message));
    }
}

I actually solved all of the overflow issues by using a blocking queue — Nissim, Jul 26 '12 at 10:15

What's the best practice to recover from a FileSystemWatcher error?

2 Answers2

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