OPTIONS ON I/O RACE CONDITION POLICY
Set internal file locking rules by calling File::Util::flock_rules()
with a list or array containing your chosen directive keywords by order
of precedence.
ex- flock_rules( qw/ BLOCK FAIL / ); # this is the default rule
KEYWORDS
BLOCK waits to try getting an exclusive lock
FAIL fails with stack trace
WARN CORE::warn() about the error with a stack trace
IGNORE ignores the failure to get an exclusive lock
UNDEF returns undef
ZERO returns 0