Unify OwnedRef and ScopedRef

[asfimport]

Currently OwnedRef and ScopedRef have similar semantics with small differences. Furtheremore, the naming distinction isn't obvious.

I propose to unify them as a single OwnedRef class with the following characteristics:

• doesn't take the GIL automatically

• has a release() method that decrefs the pointer (and sets the internal copy to NULL) before returning it

• has a detach() method that returns the pointer (and sets the internal copy to NULL) without decrefing it

  For the rare situations where an OwnedRef may be destroyed with the GIL released, a OwnedRefNoGIL derived class would also be proposed (the naming scheme follows Cython here).

  Opinions / comments?

Reporter: Antoine Pitrou / @pitrou
Assignee: Antoine Pitrou / @pitrou

PRs and other links:

• GitHub Pull Request #1534

_{Note: This issue was originally created as ARROW-2052. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Other remark : the release() method on C++ smart pointers don't decrement the underlying reference count, so deviating from that may be confusing.

[asfimport]

Wes McKinney / @wesm:
Sounds good to me. Acquiring the GIL in the destructor of OwnedRef seemed a bit unclean to me, so I think it would be better to be explicit about holding the GIL externally whenever a managed reference may go out of scope.

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1534
#1534