[dancer-users] Lock session files with Dancer2::Session::YAML?

[Maxwell Carey]

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?