version2/src/java/iotcloud/SlotBuffer.java

   1 package iotcloud;
   2
   3 /**
   4  * Circular buffer that holds the live set of slots.
   5  * @author Brian Demsky
   6  * @version 1.0
   7  */
   8
   9 class SlotBuffer {
  10         static final int DEFAULT_SIZE = 128;
  11
  12         private Slot[] array;
  13         private int head;
  14         private int tail;
  15         public long oldestseqn;
  16
  17         SlotBuffer() {
  18                 array = new Slot[DEFAULT_SIZE + 1];
  19                 head = tail = 0;
  20                 oldestseqn = 0;
  21         }
  22
  23         int size() {
  24                 if (head >= tail)
  25                         return head - tail;
  26                 return (array.length + head) - tail;
  27         }
  28
  29         int capacity() {
  30                 return array.length - 1;
  31         }
  32
  33         void resize(int newsize) {
  34                 if (newsize == (array.length - 1))
  35                         return;
  36                 Slot[] newarray = new Slot[newsize + 1];
  37                 int currsize = size();
  38                 int index = tail;
  39                 for (int i = 0; i < currsize; i++) {
  40                         newarray[i] = array[index];
  41                         if ((++index) == array.length)
  42                                 index = 0;
  43                 }
  44                 array = newarray;
  45                 tail = 0;
  46                 head = currsize;
  47         }
  48
  49         private void incrementHead() {
  50                 head++;
  51                 if (head >= array.length)
  52                         head = 0;
  53         }
  54
  55         private void incrementTail() {
  56                 tail++;
  57                 if (tail >= array.length)
  58                         tail = 0;
  59         }
  60
  61         void putSlot(Slot s) {
  62
  63                 long checkNum = (getNewestSeqNum() + 1);
  64
  65                 if (checkNum != s.getSequenceNumber()) {
  66                         // We have a gap so expunge all our slots
  67                         oldestseqn = s.getSequenceNumber();
  68                         tail = 0;
  69                         head = 1;
  70                         array[0] = s;
  71                         return;
  72                 }
  73
  74                 array[head] = s;
  75                 incrementHead();
  76
  77                 if (oldestseqn == 0) {
  78                         oldestseqn = s.getSequenceNumber();
  79                 }
  80
  81                 if (head == tail) {
  82                         incrementTail();
  83                         oldestseqn++;
  84                 }
  85         }
  86
  87         Slot getSlot(long seqnum) {
  88                 int diff = (int) (seqnum - oldestseqn);
  89                 int index = diff + tail;
  90
  91                 if (index < 0) {
  92                         // Really old message so we dont have it anymore
  93                         return null;
  94                 }
  95
  96                 if (index >= array.length) {
  97                         if (head >= tail) {
  98                                 return null;
  99                         }
 100                         index -= array.length;
 101                 }
 102
 103                 if (index >= array.length) {
 104
 105                         return null;
 106                 }
 107                 if (head >= tail && index >= head) {
 108                         return null;
 109                 }
 110
 111                 return array[index];
 112         }
 113
 114         long getOldestSeqNum() {
 115                 return oldestseqn;
 116         }
 117
 118         long getNewestSeqNum() {
 119                 return oldestseqn + size() - 1;
 120         }
 121 }