Comment 2 for bug 1793509

Reviewed: https://review.fuel-infra.org/39302
Submitter: Pkgs Jenkins <email address hidden>
Branch: 9.0/mitaka

Commit: 6d5e6dd9d6cf92136ba63ec6971349435df92b96
Author: Chaynika Saikia <email address hidden>
Date: Fri Sep 21 09:01:08 2018

Fix backup/restore error for ceph rbd backend

If a large volume is backed up or a lot of concurrent backups happen,
the cinder-backup service goes offline since a lot of these operations
have calls to the C code which are not run on native threads.

When many concurrent backup create/restore operations happen, then
if all of them are greenthreads, and since, when there is a call to the
C code, monkeypatching does not happen by eventlet. Hence, there is no
context switch to other threads until the call to the C library is
completed. This will block context switching to other green threads.
As a result, some of the backup create/restore operations might go to
error state.

The objects on which read/write operations or C function
calls are done are wrapped in Proxy objects so that they run as native
threads.

Change-Id: I75058c36085eb1a8adb26a95297e3a2039745a2c
Closes-Bug: #1793509
(cherry picked from commit f1d681875cd3b28860d7daab53695bad618900a3)