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lib/IPC/DirQueue.pm  view on Meta::CPAN

    #    E      |          enq                      enq     |
    #    D      |    stat       pickup_queued_job           |

    # the enqueuer process E enqueues a job just after the stat, inside the
    # 1-second period "t".  dequeuer process D dequeues it with
    # pickup_queued_job(). all is well.  But then, E enqueues another job
    # inside the same 1-second period "t", and since the stat() has already
    # happened for "t", and since we've already picked up the job in "t", we
    # don't recheck; result is, we miss this enqueue event.
    #
    # Avoid this by checking in a busy-loop until time(2) says we're out of
    # that "danger zone" 1-second period.  Any further enq's would then
    # cause stat(2) to report a different timestamp.

    while (time == $qdirlaststat) {
      Time::HiRes::usleep ($pollintvl);
      dbg "wait_for_queued_job: spinning until time != stat $qdirlaststat";
      my $job = $self->pickup_queued_job();
      if ($job) { return $job; }
    }