QUEUE OF AVAILABLE ELEMENTS           QUEUE FOR A DEVICE HANDLER

         +--------+                      LQE: Q1
I.QHDR:  |   Q2   |--+                   CQE: Q1
         +--------+  |
                     |
                     |                           +--------+
                     |                    Q1:    |    0   |
                     |                           +--------+
                     |                           |        |
                     |                           |        |
                     |                           +--------+
                     |
         +--------+  |
Q2:   +--|   Q3   |<-+
      |  +--------+
      |  |        |
      |  |        |
      |  +--------+
      |
      |  +--------+
Q3:   +->|    0   |
         +--------+
         |        |
         |        |
         +--------+