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 > > > > _______________________________________________ > OpenStack-dev mailing list > OpenStack-dev@lists.openstack.org > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
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