Driver Management

[yeesian]

https://sgillies.net/2014/01/22/rethinking-driver-management-in-fiona-and-rasterio.html

Maybe we should not register all the drivers when importing the module, since we do not call GDALDestroyDriverManager()?

[visr]

Sean writes about problems with Python's atexit module.
Do we also have these problems? Could we for instance add a finalizer to the module itself? I tried some things, but not sure how to test if it is working.

julia> module A
       f(A) = println("cleaning up...")
       finalizer(A, f)
       end
A

julia> module A; end
WARNING: replacing module A
A

julia> gc()
cleaning up...error in running finalizer: ErrorException("task switch not allowed from inside gc finalizer")

finalizer(GDAL, GDAL.destroydrivermanager)
finalizer(GDAL, GDAL.destroy)

[yeesian]

Could we for instance add a finalizer to the module itself?

I don't think we can: JuliaLang/julia#8764.

The deeper issue is that it isn't clean for driver registration to be a side-effect of importing the module; and it won't be possible for downstream packages to reverse that.

[visr]

Ah thanks for the link. Ok I agree on the side-effect not being very clean. Shall we just remove the driver register functions from the __init__, or also provide a context manager function in this package?

[yeesian]

I think removing the driver registration functions from __init__ should be fine. There still isn't a particularly clean solution to (automatically) decide which functions to provide do-block equivalents for. Some relevant reading: https://lists.osgeo.org/pipermail/gdal-dev/2010-September/026027.html

[meggart]

I am trying to catch up a bit with your progress, so sorry for stupid questions. Would this mean that the driver registration and destruction would have to be handled by the user? How would a downstream package handle this?

[yeesian]

Yup,

This would mean that driver registration and destruction will have to be handled by downstream packages/users, e.g.

import GDAL
GDAL.allregister()
...
GDAL.destroydrivermanager()

A downstream package might provide a do-block context e.g.

module FriendlierGDAL
import GDAL
function registerdrivers(f::Function)
   GDAL.allregister()
   try
      f()
   finally
      GDAL.destroydrivermanager()
   end
end
end

Such that users can do something like

import FriendlierGDAL
FriendlierGDAL.registerdrivers() do
   ...
end