If the last reference to a Python object is at module scope, when
its destructor is run before program termination it may find that
the globals it requires no longer exist. Destructors of objects
likely to be stored at module global scope need to check that
globals exist before attempting to use them, to avoid warnings
being printed by the Python interpreter.
See grpc#17004
* unit test included
* throw ValueError exception from Cython to Python
* prevent the deconstruction method from failing when Channel initialization failed
A process may fork after invoking grpc_init() and use gRPC in the child
if and only if the child process first destroys all gRPC resources
inherited from the parent process and invokes grpc_shutdown().
Subsequent to this, the child will be able to re-initialize and use
gRPC. After fork, the parent process will be able to continue to use
existing gRPC resources such as channels and calls without interference
from the child process.
To facilitate gRPC Python applications meeting the above constraints,
gRPC Python will automatically destroy and shutdown all gRPC Core
resources in the child's post-fork handler, including cancelling
in-flight calls (see detailed design below). From the client's
perspective, the child process is now free to create new channels and
use gRPC.
Module level loggers were introduced to gRPC Python in 06e1683, but
missed configuring these, leading to 'No handler found for module'
errors. Using the root logger implicitly calls basicConfig() which does
the basic configuration for the logging system by creating a
StreamHandler with a default Formatter and adding it to the logger. But
this is not the case for module level loggers.
Fix this issue by explicitly calling logging.basicConfig().