Is it possible to lock session files created by Dancer2::Session::YAML in order to avoid race conditions when two processes try to write to the same session at the same time? For example, if I have the following routes: get '/foo' => sub { my $foo = session 'foo'; session 'foo' => ++$foo; }; get '/bar' => sub { my $bar = session 'bar'; session 'bar' => ++$bar; }; and both are called at the same time, one route "wins", resulting in either the value of 'foo' or 'bar' being updated, but not both. If it's not possible (or easy) to lock the file, I would be open to an alternative storage backend, although I was hoping to keep things as simple as possible, i.e. I don't want to have to spin up a new MySQL database or equivalent. The existing Dancer2::Session:: backends all seem somewhat...involved. Any ideas?