David Allsopp wrote:
> Probably irrelevant here, but this approach wouldn't work under Windows
> (Unix.file_descr is the Win32 file handle at that point which is often
> larger than 1024). More relevantly, Unix can be reconfigured to allow for
> more than 1024 open files.

Yes, I assumed that this would be non-portable, and that is yet another 
problem. It seems that dropping down to C is the only way to really do 
this right.

> Wouldn't an easier, portable way be to wrap Unix.openfile and Unix.close to
> maintain a set of open file_descrs or is your concern the risk of files left
> open by third party code?

The latter. The simple solution is to use Unix.set_close_on_exec from 
the parent process, but that only works if it's under my control.

Dave