Platform independent file locking?

Question

I'm running a very computationally intensive scientific job that spits out results every now and then. The job is basically to just simulate the same thing a whole bunch of times, so it's divided among several computers, which use different OSes. I'd like to direct the output from all these instances to the same file, since all the computers can see the same filesystem via NFS/Samba. Here are the constraints:

1. Must allow safe concurrent appends. Must block if some other instance on another computer is currently appending to the file.
2. Performance does not count. I/O for each instance is only a few bytes per minute.
3. Simplicity does count. The whole point of this (besides pure curiosity) is so I can stop having every instance write to a different file and manually merging these files together.
4. Must not depend on the details of the filesystem. Must work with an unknown filesystem on an NFS or Samba mount.

The language I'm using is D, in case that matters. I've looked, there's nothing in the standard lib that seems to do this. Both D-specific and general, language-agnostic answers are fully acceptable and appreciated.

Answer 1

Over NFS you face some problems with client side caching and stale data. I have written an OS independent lock module to work over NFS before. The simple idea of creating a [datafile].lock file does not work well over NFS. The basic idea to work around it is to create a lock file [datafile].lock which if present means file is NOT locked and a process that wants to acquire a lock renames the file to a different name like [datafile].lock.[hostname].[pid]. The rename is an atomic enough operation that works well enough over NFS to guarantee exclusivity of the lock. The rest is basically a bunch of fail safe, loops, error checking and lock retrieval in case the process dies before releasing the lock and renaming the lock file back to [datafile].lock