More specifically, I envision restart to work like this:

1) user invokes user-land utility (e.g. "cr --restart ..."
2) 'cr' will create a new container
3) 'cr' will start a child in that container

process 1 in its private namespaces.

4) child will create rest of tree (in kernel or in user space - tbd)
5) each task in that tree will restore itself
6) 'cr' monitors this process
7) if all goes well - 'cr' report ok.
8) if something goes bad, 'cr' notices and notifies caller/user

that's MCR implementation of restart. 
 

so tasks that are restarting may just as well die badly - we don't care.

just sigkill them, but at end, before releasing the container from 
a frozen state, we have to make sure the right number of tasks have 
restarted ... so you need to track them along the way.

C.