QUEUE OF AVAILABLE ELEMENTS           QUEUE FOR A DEVICE HANDLER

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