batch processing in GRASS

[Precision Farming Project]

Hi:
   Recently, one of my users has (inadvertently) gotten
into the situation where multiple instances of EXACTLY
the same GRASS job have been run in the background.
This is on a Linux installation.  All the programs
are working with the same region of data, which shouldn't
be a problem, and all of them are using the same file
for input (which is not being modified by any of the
programs).  But what I am having problems understanding
is how GRASS can let multiple jobs write to the same 
file?  Doesn't GRASS grant the first program to run an
exclusive write file lock?  Shouldn't the remaining
GRASS programs die since they cannot get write access on
the file?

   If this is "in the manual", I am sorry for asking.
I am trying to wade through it now, but the first couple of
places I looked didn't seem to address this.

Thanks.
Gordon Haverland
Precision Farming Project
Alberta Agriculture
ghaverla at freenet.edmonton.ab.ca
goddard at gpu.ualberta.ca