An instance of this class tracks all StackedObjectProxy state in existence when unexpected exceptions are raised by WSGI applications housed by EvalException and RegistryManager. Like EvalException, this information is stored for the life of the process.

When an unexpected exception occurs and EvalException is present in the WSGI stack, save_registry_state is intended to be called to store the Registry state and enable automatic restoration on all currently registered StackedObjectProxies.

With restoration enabled, those StackedObjectProxies' _current_obj (overwritten by _current_obj_restoration) method's strategy is modified: it will return its appropriate proxied object from the restorer when a restoration context is active in the current thread.

The StackedObjectProxies' _push/pop_object methods strategies are also changed: they no-op when a restoration context is active in the current thread (because the pushing/popping work is all handled by the Registry/restorer).

The request's Registry objects' reglists are restored from the restorer when a restoration context begins, enabling the Registry methods to work while their changes are tracked by the restorer.

The overhead of enabling restoration is negligible (another threadlocal access for the changed StackedObjectProxy methods) for normal use outside of a restoration context, but worth mentioning when combined with StackedObjectProxies normal overhead. Once enabled it does not turn off, however:

o Enabling restoration only occurs after an unexpected exception is detected. The server is likely to be restarted shortly after the exception is raised to fix the cause

o StackedObjectRestorer is only enabled when EvalException is enabled (not on a production server) and RegistryManager exists in the middleware stack