That reminds me of a very useful bit of information reguarding locking. A single lock variable can be used to control access to multiple shared variables. For example,
my $list_head : shared; # Access controlled by $list_head.
my $list_tail : shared; # Access controlled by $list_head.
sub ... {
...
{
lock($list_head);
... code that uses $list_head and/or $list_tail ...
}
...
}
It doesn't matter which variable is used as to control access to a give shared variable, as long as you *always* use the same lock variable to control access to that shared variable.