src/it/lilik/capturemjpeg/CircularBuffer.java

   1 /*
   2         This file is part of CaptureMJPEG.
   3
   4     CaptureMJPEG is free software: you can redistribute it and/or modify
   5     it under the terms of the GNU Lesser Public License as published by
   6     the Free Software Foundation, either version 3 of the License, or
   7     (at your option) any later version.
   8
   9     CaptureMJPEG is distributed in the hope that it will be useful,
  10     but WITHOUT ANY WARRANTY; without even the implied warranty of
  11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12     GNU Lesser Public License for more details.
  13
  14     You should have received a copy of the GNU Lesser Public License
  15     along with CaptureMJPEG.  If not, see <http://www.gnu.org/licenses/>.
  16
  17     Copyright (c) 2008 - Alessio Caiazza, Cosimo Cecchi
  18  */
  19 package it.lilik.capturemjpeg;
  20
  21 import java.io.ByteArrayInputStream;
  22
  23 /**
  24  * A circular buffer of {@link java.io.ByteArrayInputStream}
  25  *
  26  * @author Alessio Caiazza
  27  * @author Cosimo Cecchi
  28  *
  29  */
  30 class CircularBuffer {
  31
  32         /** data storage */
  33         private ByteArrayInputStream buffer[];
  34         /** last item in <code>CircularBuffer</code> */
  35         private int lastIdx;
  36         /** first valid item in <code>CircularBuffer</code> */
  37         private int firstIdx;
  38         /** size of <code>CircularBuffer</code> */
  39         private int size;
  40
  41         private boolean empty;
  42
  43         /** default size */
  44         static final int DEFAULT_SIZE = 5;
  45
  46         /**
  47          * Creates a new <code>CircularBuffer</code> with
  48      * the specified size.
  49          * @param size the size of the buffer.
  50          */
  51         public CircularBuffer(int size) {
  52                 this.size = size;
  53                 this.firstIdx = 0;
  54                 this.lastIdx = 0;
  55                 this.empty = true;
  56                 this.buffer = new ByteArrayInputStream[size];
  57         }
  58
  59         /**
  60          * Creates a <code>CircularBuffer</code> with
  61      *  internel buffer of
  62      * {@link it.lilik.capturemjpeg.CircularBuffer#DEFAULT_SIZE}
  63          */
  64         public CircularBuffer() {
  65                 this(CircularBuffer.DEFAULT_SIZE);
  66         }
  67
  68         /**
  69          * Adds a an element to the <code>CircularBuffer</code>
  70          *
  71          * @param data the new element
  72          */
  73         public synchronized void push(ByteArrayInputStream data) {
  74                 buffer[this.lastIdx] = data;
  75                 if( this.lastIdx == this.firstIdx && !this.empty) {
  76                         //we have overwritten an element
  77                         //System.out.print("overwrite ");
  78                         this.firstIdx++;
  79                         this.firstIdx %= this.size;
  80                 }
  81                 if (this.empty)
  82                         this.empty = false;
  83                 this.lastIdx++;
  84                 this.lastIdx %= this.size;
  85                 //System.out.println("Pushed (" + getLength() + ")");
  86         }
  87
  88         /**
  89          * Returns the  number of elements into the buffer
  90          * @return the number of valid elements
  91          */
  92         public synchronized int getLength() {
  93                 if (this.empty)
  94                         return 0;
  95                 int len = this.lastIdx - this.firstIdx;
  96                 if (len < 0)
  97                         len = this.size + len;
  98                 return len == 0 ? this.size-1 : len;
  99         }
 100
 101
 102         /**
 103          * Gets the first available element.
 104          *
 105          * @return the first element
 106          * @throws IndexOutOfBoundsExceptions
 107          */
 108         public synchronized ByteArrayInputStream pop() {
 109                 if (isEmpty()) {
 110                         //TODO:change Exception type
 111                         throw new IndexOutOfBoundsException("Empty buffer");
 112                 }
 113                 ByteArrayInputStream res = buffer[this.firstIdx];
 114                 buffer[this.firstIdx] = null;
 115                 this.firstIdx++;
 116                 this.firstIdx %= this.size;
 117                 if (this.firstIdx == this.lastIdx)
 118                         this.empty = true;
 119                 //System.out.println("Popped (" + getLength() + ")");
 120                 return res;
 121         }
 122
 123         /**
 124          * Returns the status of the buffer.
 125          * @return <code>true</code> if empty, otherwise <code>false</code>
 126          */
 127         public synchronized boolean isEmpty() {
 128                 return this.empty;
 129         }
 130
 131         /**
 132      * Returns the size of the buffer.
 133      *
 134      * @return the size of the buffer.
 135      */
 136         public int getSize() {
 137                 return this.size;
 138         }
 139 }