src/main/java/eu/svjatoslav/sixth/data/store/file/MetaData.java

   1 /*
   2  * Sixth Data. Author: Svjatoslav Agejenko.
   3  * This project is released under Creative Commons Zero (CC0) license.
   4  *
   5 */
   6
   7 package eu.svjatoslav.sixth.data.store.file;
   8
   9 import java.io.IOException;
  10
  11 public class MetaData {
  12
  13     public static final int FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START = 4 * 6;
  14     private static final int FORMAT_VERSION = 1;
  15     private static final int FILE_LOCATION_VERSION = 4 * 0;
  16     private static final int FILE_LOCATION_ENTRIES_TABLE_SIZE = 4 * 1;
  17     private static final int FILE_LOCATION_USED_ENTRIES_COUNT = 4 * 2;
  18     private static final int FILE_LOCATION_CURRENT_ENTRY = 4 * 3;
  19     private static final int FILE_LOCATION_CURRENT_LOCATION = 4 * 4; // LONG!!
  20     private final FileDataStore dataStore;
  21     private int entriesTableSize;
  22     private int currentEntry;
  23     private int usedEntriesCount;
  24     private long currentLocation;
  25
  26     public MetaData(final FileDataStore dataStore) {
  27         this.dataStore = dataStore;
  28     }
  29
  30     /**
  31      * @return address of the start of the allocated space
  32      */
  33     public synchronized long allocateStorageSpace(final int amountOfBytes) {
  34         final long locationStart = currentLocation;
  35         currentLocation += amountOfBytes;
  36         return locationStart;
  37     }
  38
  39     public void decreaseUsedEntriesCount() {
  40         usedEntriesCount--;
  41     }
  42
  43     public synchronized void ensureMinimumCurrentLocation(
  44             final long minimumLocation) {
  45
  46         if (currentLocation < minimumLocation)
  47             currentLocation = minimumLocation;
  48     }
  49
  50     public boolean entriesTableNeedsIncreasing() {
  51         final int reserveSize = (entriesTableSize / 10) + 1;
  52
  53         return usedEntriesCount >= (entriesTableSize - reserveSize);
  54
  55     }
  56
  57     public long getEntriesStorageAreaStart() {
  58         return FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START
  59                 + (EntryRecord.ENTRY_RECORD_LENGTH * entriesTableSize);
  60     }
  61
  62     public long getEntriesStorageAreaStart(
  63             final int hypotheticalEntriesTableSize) {
  64         return FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START
  65                 + (EntryRecord.ENTRY_RECORD_LENGTH * hypotheticalEntriesTableSize);
  66     }
  67
  68     /**
  69      * @return amount of entries in the entries table
  70      */
  71     public int getEntriesTableSize() {
  72         return entriesTableSize;
  73     }
  74
  75     public void setEntriesTableSize(final int newSize) {
  76         entriesTableSize = newSize;
  77     }
  78
  79     public int getNewEntryId() {
  80         currentEntry++;
  81
  82         if (currentEntry >= getEntriesTableSize())
  83             currentEntry = 0;
  84
  85         return currentEntry;
  86     }
  87
  88     public void increaseUsedEntriesCount() {
  89         usedEntriesCount++;
  90     }
  91
  92     public void initializeNewFile() throws IOException {
  93         entriesTableSize = 16;
  94         usedEntriesCount = 0;
  95         currentEntry = entriesTableSize - 1;
  96         currentLocation = getEntriesStorageAreaStart();
  97
  98         writeFileHeader();
  99     }
 100
 101     public void readFileHeader() throws IOException {
 102
 103         final int fileVersion = dataStore.readInt(FILE_LOCATION_VERSION);
 104         if (fileVersion != FORMAT_VERSION)
 105             throw new RuntimeException("File version is " + fileVersion
 106                     + " but version " + FORMAT_VERSION + " is required.");
 107
 108         entriesTableSize = dataStore.readInt(FILE_LOCATION_ENTRIES_TABLE_SIZE);
 109
 110         usedEntriesCount = dataStore.readInt(FILE_LOCATION_USED_ENTRIES_COUNT);
 111
 112         currentEntry = dataStore.readInt(FILE_LOCATION_CURRENT_ENTRY);
 113
 114         currentLocation = dataStore.readLong(FILE_LOCATION_CURRENT_LOCATION);
 115     }
 116
 117     public void setCurrentLocation(final long currentLocation) {
 118         this.currentLocation = currentLocation;
 119     }
 120
 121     public void writeFileHeader() throws IOException {
 122         dataStore.writeInt(FILE_LOCATION_VERSION, FORMAT_VERSION);
 123         dataStore.writeInt(FILE_LOCATION_ENTRIES_TABLE_SIZE,
 124                 getEntriesTableSize());
 125         dataStore.writeInt(FILE_LOCATION_USED_ENTRIES_COUNT, usedEntriesCount);
 126         dataStore.writeInt(FILE_LOCATION_CURRENT_ENTRY, currentEntry);
 127         dataStore.writeLong(FILE_LOCATION_CURRENT_LOCATION, currentLocation);
 128     }
 129
 130 }