Is it reasonable to expect to share DL_DIR between multiple builds?

That is, are downloads properly locked so that multiple concurrent downloads of the same file won't collide? And if so, are they NFS safe locks?

Or must each build download it's own copies of every component?

I ask because our, (Palm), branch has been, but it's a bit of a nuisance to pick a suitable locking mechanism that is both functional and performant.

Flock/lockf aren't reliably supported in heterogeneous environments.
The old lockfiles don't work over NFS. Lock directories apparently do, but trying to clean these up after interruptions or failures is a losing battle so if we do use these, we end up with orphan locks periodically.
With NFS as a possibility, we can't assume any kernel local IPC mechanism, so sysV ipc is out.
It seems like a pretty huge overhead to try to create any sort of zeroconf overhead.

Our solution so far has been to use NFS lock directories for multiple machine builds and flock/lockf for single machine builds. This mostly works, though it's not ideal, and it's significantly faster than downloading/copying all of the component source multiple times even over local mirrors.

--rich