There are reliable and portable ways to prevent such race conditions easily from Perl. Unfortunately, IPC::DirQueue seems disappointingly naive on this point:

# now, we want to try to avoid 2 or 3 dequeuers removing
# the lockfile simultaneously, as that could cause this race:
#
# dqproc1: [checks file]        [unlinks] [starts work]
# dqproc2:        [checks file]                         [unlinks]
#
# ie. the second process unlinks the first process' brand-new
# lockfile!
#
# to avoid this, use a random "fudge" on the timeout, so
# that dqproc2 will wait for possibly much longer than
# dqproc1 before it decides to unlink it.
#
# this isn't perfect.  TODO: is there a "rename this fd" syscall
# accessible from perl?
[download]