Hi, all:
I find almost all of the @utils.synchronized decoration usage in
cinder-volume (cinder.volume.manager / cinder.volume.drivers.*) with an
"external=True" param. Such as
cinder.volume.manager.VolumeManager:attach_volume:
def attach_volume(self, context, volume_id, instance_uuid,
host_name,
mountpoint, mode):
"""Updates db to show volume is attached."""
@utils.synchronized(volume_id, external=True)
def do_attach():
However, in docstring of common.lockutils.synchronized, I find param
"external" is used for multi-workers scenario:
:param external: The external keyword argument denotes whether
this lock
should work across multiple processes. This means that if two different
workers both run a a method decorated with @synchronized('mylock',
external=True), only one of them will execute at a time.
I have two questions about it.
1. As far as I know, cinder-api has supported multi-worker mode and
cinder-volume doesn't support it, does it? So I wonder why the "external=True"
param is used here?
2. Specific to cinder.volume.manager.VolumeManager:attach_volume, all
operations in "do_attach" method are database related. As said in [1],
operations to the database will block the main thread of a service, so another
question I want to know is why this method is needed to be synchronized?
Thanks.
[1]
http://docs.openstack.org/developer/cinder/devref/threading.html#mysql-access-and-eventlet
----------
zhangleiqiang (Trump)
Best Regards
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