On Apr 26, 2014, at 2:56 AM, Zhangleiqiang (Trump) <zhangleiqi...@huawei.com> wrote:
> 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?
Before the multibackend support in cinder-volume it was common to run more than
one cinder-volume for different backends on the same host. This would require
external=True
> 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?
Currently db operations block the main thread of the service, but hopefully
this will change in the future.
Vish
>
> Thanks.
>
> [1]
> http://docs.openstack.org/developer/cinder/devref/threading.html#mysql-access-and-eventlet
> ----------
> zhangleiqiang (Trump)
>
> Best Regards
>
>
>
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