User Profile Service Application stuck in Synchronization state

I had a User Profile Synchronization job stuck in the Synchronizing state. Clicking Stop did nothing. I also tried stopping the User Profile Synchronization Service, but got the following error:

An update conflict has occurred, and you must re-try this action. The object UserProfileApplication Name=User Profile Service Application was updated by [farm admin id], in the OWSTIMER (7292) process, on machine [machine name].  View the tracing log for more information about the conflict.

I didn't see anything more helpful in the ULS logs, but I did see the same errors in the Application Log (Event Viewer)

Apparently, this is due to a well known problem with the cache in SharePoint 2010 (although it would be nice to know the cause). In any case, here's how you would fix it (as described in An update conflict has occurred, and you must re-try this action, but adapted to SharePoint 2010).

1. Stop the timer service by doing the following:
1. Click Start->Administrative Tools->Services
2. Right click SharePoint 2010 Timer, select Stop
2. Delete the contents of the folder: C:\ProgramData\Microsoft\SharePoint\Config\<some GUID>
3. Start the timer service by doing the following
1. Click Start->Administrative Tools->Services
2. Right click SharePoint 2010 Timer, select Start

Once the timer is restarted, the cache folder will rebuild itself.

I was then able to go back into Manage my User Profile Service Application and stop the running sync job.