R – How does FileSystemWatcher work on another computers directory

.netdesign-patternsfilesystemwatcherwinapi

Something intrigues me and I don't find any resource on this.

How can FileSystemWatcher know when a file on a computer "A" is created/removed/changed/renamed ?

I thought that this worked with polling, (the observer polls the server to check update), but after verifying the network activity with Wireshark I saw that polling was not used.
Does the SMB protocol use a observable/observer pattern ?

In this case how the server can know when a client doesn't observe him anymore ?

What is the consequence when the network falls during an observation and comes back right after?

Using FileSystemWatcher on another computer seems too easy to be true…

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Using FileSystemWatcher on another computer seems too easy to be true...

It kinda is. The underlying API - ReadDirectoryChanges() - opens up a connection to the server, which is responsible for responding when something changes. If that connection gets dropped for some reason, or you bump up against the connection limit of the OS you're connecting to, then you don't get notifications.

I've found that it is more reliable to poll periodically (with some rather long interval), and use FileSystemWatcher only as a way of responding quickly to changes in between polls.

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C# – How to update the GUI from another thread

The simplest way is an anonymous method passed into Label.Invoke:

// Running on the worker thread
string newText = "abc";
form.Label.Invoke((MethodInvoker)delegate {
    // Running on the UI thread
    form.Label.Text = newText;
});
// Back on the worker thread

Notice that Invoke blocks execution until it completes--this is synchronous code. The question doesn't ask about asynchronous code, but there is lots of content on Stack Overflow about writing asynchronous code when you want to learn about it.

C# – How to get the directory from a file’s full path

If you've definitely got an absolute path, use Path.GetDirectoryName(path).

If you might only get a relative name, use new FileInfo(path).Directory.FullName.

Note that Path and FileInfo are both found in the namespace System.IO.

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C# – How to update the GUI from another thread

C# – How to get the directory from a file’s full path

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