[systemd-devel] Are transactions (state change requests) serialized?

[Andrey Borzenkov]

I request to start unit - "systemctl start foo.target". This computes
foo dependencies and requirements and initiate transaction. What
happens if another request (say, systemctl start bar.target) comes
while the first one is still being processed? In this case foo and bar
are two completely separate units that do not have anything in common,
and actions can be start or stop - again it does not matter.

To be more precise - will systemd wait until foo.target with all
dependencies is started or will it initiate bar.target transaction in
parallel while foo.target is still running?