I'm working on something very similar, and I can tell you for a fact that NFS complicates things considerably.

These resources were incredibly helpful:

Essentially, the first time you ask NFS for a file (via stat or open) it will check the filesystem. For the next 3 seconds (by default) , any stat call is checked against the attribute cache instead of the actual file. This means that even though you check for existence (-e $file), NFS can and will lie to you.

With a directory, the same thing is true - NFS has a filehandle cache. The first time you readdir on the directory, NFS caches that response for 3 seconds afterwards. So files can be deleted by other NFS clients and (again) NFS will lie to you.

From the Linux NFS faq http://nfs.sourceforge.net/:

After a file is deleted on the server, clients don't find out until they try to access the file with a file handle they had cached from a previous LOOKUP. Using rsync or mv to replace a file while it is in use on another client is a common scenario that results in an ESTALE error.

The NFS Coding how-to has suggestions on how to work around the NFS cache as a programmer. It also has a C utility that you can download and compile on two different servers that share the NFS storage so you can determine which workarounds work and which don't.

In general, open + close on the file and touching the directory *should* clear the caches on most Linux/Unix operating systems. VMS and Windows are a bit different though, so definitely utilize the resources above before they vanish into the dark recesses of the interwebs.

In reply to Re^5: Synchronizing multiple processes retrieving files out of shared directory by Ravenhall
in thread Synchronizing multiple processes retrieving files out of shared directory by MitchInOmaha

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