| 1 | package de.uka.ipd.sdq.sensorframework.storage.lists; |
| 2 | |
| 3 | import java.io.File; |
| 4 | import java.io.IOException; |
| 5 | import java.io.RandomAccessFile; |
| 6 | import java.util.AbstractList; |
| 7 | import java.util.List; |
| 8 | import java.util.RandomAccess; |
| 9 | |
| 10 | /** |
| 11 | * @author Steffen Becker |
| 12 | * A generic list implementation that consumes a constant amount of main memory regardless of the number of elements in the |
| 13 | * list. It relies on HDD memory as background storage. It uses chunks which are filled and upon fully filled swapped to disk. |
| 14 | * The list has some restrictions for this to work. First, all elements have to be serialisable with constant memory footprint. Second, |
| 15 | * deletion of elements in the list is not implemented. |
| 16 | * @param <T> The generic type parameter of the list's elements |
| 17 | */ |
| 18 | public class BackgroundMemoryList<T> |
| 19 | extends AbstractList<T> |
| 20 | implements List<T>, RandomAccess { |
| 21 | |
| 22 | /** |
| 23 | * Number of list elements per list chunk |
| 24 | */ |
| 25 | static final public int MEMORY_CHUNKS_SIZE = 10000; |
| 26 | |
| 27 | /** |
| 28 | * The current chunk loaded into memory |
| 29 | */ |
| 30 | private Chunk<T> currentChunk = null; |
| 31 | |
| 32 | /** |
| 33 | * The background file storage in which all chunks get persisted when they are swapped from main memory |
| 34 | */ |
| 35 | private RandomAccessFile raf = null; |
| 36 | |
| 37 | /** |
| 38 | * Inner state of the underlying background storage |
| 39 | */ |
| 40 | boolean isClosed = true; |
| 41 | |
| 42 | /** |
| 43 | * The serialiser used to serialise the elements of the list on the background storage |
| 44 | */ |
| 45 | private ISerialiser<T> serialiser; |
| 46 | |
| 47 | /** |
| 48 | * Current number of elements in the list |
| 49 | */ |
| 50 | private int listSize; |
| 51 | |
| 52 | /** |
| 53 | * Constructor of a background memory list |
| 54 | * @param filename The file used as background storage |
| 55 | * @param serialiser The serialiser used to serialise the elements of the list |
| 56 | * @throws IOException Thrown if file IO fails |
| 57 | */ |
| 58 | public BackgroundMemoryList(String filename, ISerialiser<T> serialiser) throws IOException { |
| 59 | this(new File(filename),serialiser); |
| 60 | } |
| 61 | |
| 62 | /** |
| 63 | * Constructor of a background memory list |
| 64 | * @param f The file used as background storage |
| 65 | * @param serialiser The serialiser used to serialise the elements of the list |
| 66 | * @throws IOException Thrown if file IO fails |
| 67 | */ |
| 68 | public BackgroundMemoryList(File f, ISerialiser<T> serialiser) throws IOException { |
| 69 | raf = new RandomAccessFile(f,"rw"); |
| 70 | isClosed = false; |
| 71 | this.serialiser = serialiser; |
| 72 | initListSize(); |
| 73 | } |
| 74 | |
| 75 | @Override |
| 76 | public synchronized void add(int index, T e) { |
| 77 | try{ |
| 78 | ensureCorrectChunkLoaded(index); |
| 79 | if (currentChunk == null || currentChunk.isFull()) { |
| 80 | flush(); |
| 81 | currentChunk = new Chunk<T>(raf,serialiser); |
| 82 | } |
| 83 | currentChunk.add(e); |
| 84 | this.listSize++; |
| 85 | } catch(IOException ex) { |
| 86 | throw new RuntimeException("Background List failed",ex); |
| 87 | } |
| 88 | } |
| 89 | |
| 90 | public synchronized T get(int index) { |
| 91 | if (this.isClosed) |
| 92 | throw new IllegalStateException("Tryed to get data from a closed background list"); |
| 93 | if (index >= size()) |
| 94 | throw new ArrayIndexOutOfBoundsException("Read behind background list length"); |
| 95 | try{ |
| 96 | ensureCorrectChunkLoaded(index); |
| 97 | return currentChunk.get((int)(index-currentChunk.fromElement())); |
| 98 | } catch(IOException ex) { |
| 99 | throw new RuntimeException("Background List failed",ex); |
| 100 | } |
| 101 | } |
| 102 | |
| 103 | /** |
| 104 | * Tests whether a chunk swapping is needed to access the list element add the given index and if so swaps the chunks |
| 105 | */ |
| 106 | private void ensureCorrectChunkLoaded(int index) throws IOException { |
| 107 | if (currentChunk != null && currentChunk.accepts(index)) |
| 108 | return; |
| 109 | else { |
| 110 | flush(); |
| 111 | currentChunk = new Chunk<T>(raf,serialiser,index / MEMORY_CHUNKS_SIZE); |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | public synchronized int size() { |
| 116 | return this.listSize; |
| 117 | } |
| 118 | |
| 119 | /** |
| 120 | * Derive the list size from the size of the underlying file. Called on opening a list |
| 121 | */ |
| 122 | private void initListSize() { |
| 123 | try { |
| 124 | if (currentChunk != null && !currentChunk.isFull()) { |
| 125 | // The current chunk is the last chunk which might contain unsaved data, |
| 126 | // so the size is the size of all saved data + all unsaved data |
| 127 | this.listSize = (int)(raf.length() / (serialiser.getElementLength() * MEMORY_CHUNKS_SIZE) + currentChunk.size()); |
| 128 | } |
| 129 | this.listSize = (int)(raf.length() / serialiser.getElementLength()); |
| 130 | } catch (IOException e) { |
| 131 | throw new RuntimeException("Background list failed unexpectedly",e); |
| 132 | } |
| 133 | } |
| 134 | |
| 135 | /** Closes the background storage. The list is inaccessible afterwards |
| 136 | * @throws IOException |
| 137 | */ |
| 138 | public synchronized void close() throws IOException { |
| 139 | if (!isClosed){ |
| 140 | flush(); |
| 141 | raf.close(); |
| 142 | isClosed = true; |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | /** Writes all buffered data to the background storage and clears the current chunk. |
| 147 | * @throws IOException |
| 148 | */ |
| 149 | public synchronized void flush() throws IOException { |
| 150 | if (currentChunk != null) { |
| 151 | currentChunk.persist(); |
| 152 | } |
| 153 | currentChunk = null; |
| 154 | } |
| 155 | } |