Shut down kernels in parallel...
Shut down kernels in parallel
When stopping the notebook server, it currently sends a shutdown request
to each kernel and then waits for the process to finish. This can be slow if
you have several kernels running. This makes it issues all the shutdown
requests before waiting on the processes, so shutdown happens in
parallel.
KernelManager (and MultiKernelManager) gain three new public API methods
to allow this:
* request_shutdown (promoted from a private method)
* wait_shutdown (refactored out of shutdown_kernel)
* cleanup (refactored out of shutdown_kernel)
