I wrote code in AX 2009 to poll a directory on a network drive, every 1 second, waiting for a response file from another system. I noticed that using a file explorer window, I could see the file appear, yet my code was not seeing and processing the file for several seconds - up to 9 seconds (and 9 polls) after the file appeared!
The AX code calls System.IO.Directory::GetFiles() using ClrInterop:
interopPerm = new InteropPermission(InteropKind::ClrInterop);
interopPerm.assert();
files = System.IO.Directory::GetFiles(#POLLDIR,'*.csv');
// etc...
CodeAccessPermission::revertAssert();
After much experimentation, it emerges that the first time in my program's lifetime, that I call ::GetFiles(), it starts a notional "ticking clock" with a period of 10 seconds. Only calls every 10 seconds find any new files that may have appeared, though they do still report files that were found on an earlier 10s "tick" since the first call to ::GetFiles().
If, when I start the program, the file is not there, then all the other calls to ::GetFiles(), 1 second after the first call, 2 seconds after, etc., up to 9 seconds after, simply do not see the file, even though it may have sitting there since 0.5s after the first call!
Then, reliably, and repeatably, the call 10s after the first call, will find the file. Then no calls from 11s to 19s will see any new file that might have appeared, yet the call 20s after the first call, will reliably see any new files. And so on, every 10 seconds.
Further investigation revealed that if the polled directory is on the AX AOS machine, this does not happen, and the file is found immediately, as one would expect, on the call after the file appears in the directory.
But this figure of 10s is reliable and repeatable, no matter what network drive I poll, no matter what server it's on.
Our network certainly doesn't have 10s of latency to see files; as I said, a file explorer window on the polled directory sees the file immediately.
What is going on?
I would guess DAXaholic's answer is correct, but you could try other solutions like EnumerateFiles.
In your case I would rather wait for the files rather than poll for the files. Using FileSystemWatcher there will be a minimal delay from file creation till your process wakes up. It is more tricky to use, but avoiding polling is a good thing. I have never used it over a network.