The functionality of this module depends on the availability of the DATA
handle in the script from which this module is called (more specifically:
in the main namespace).
At INIT time, it is checked whethere there is a DATA handle: if not, it
exits with an error message on STDERR and an exit value of 2.
If the DATA handle is available, and it cannot be flocked, it exits
silently with an exit value of 0.
If there is a DATA handle, and it could be flocked, a message is put on
STDERR and execution continues without any further interference. Optionally,
the message on STDERR can be prevented by specifying the silent parameter
in the use statement with a true value, like:
use Sys::RunAlways silent => 1;