[GRASS-dev] creating temporary mapsets in a parallelized python script

[Glynn Clements]

Vaclav Petras wrote:

> > Does this function mean that: while concurrent r.basin runs on different
> > CPUs in the same mapset, there is no interefering by region settings change
> > interefering?
> 
> Setting WIND_OVERRIDE (environmental variable) will happen for the current
> process, so it won't affect other processes only subprocess which is
> desired. (In your case, this won't work if you would use this function
> outside of r.basin.) So yes, parallel processes (including g.region) won't
> see WIND_OVERRIDE, so they will see and use the original computational
> region.

The environment will be inherited by any child processes, so a
top-level script can use the same approach (but not use_temp_region()
itself) to use a different named region for each subprocess.

The main issue with use_temp_region() is that the clean-up function
uses the current value of the environment variable to determine which
region to delete.

This could be fixed by passing a lambda to atexit.register(), e.g.

def use_temp_region():
    name = "tmp.%s.%d" % (os.path.basename(sys.argv[0]), os.getpid())
    run_command("g.region", save=name, overwrite=True)
    os.environ['WIND_OVERRIDE'] = name
    atexit.register(lambda: run_command("g.remove", flags='f', quiet=True, type='region', name=name))

-- 
Glynn Clements <glynn at gclements.plus.com>