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

   1 /*
   2  * Sixth Data. Copyright ©2012-2019, Svjatoslav Agejenko, svjatoslav@svjatoslav.eu
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of version 3 of the GNU Lesser General Public License
   6  * or later as published by the Free Software Foundation.
   7  */
   8
   9 package eu.svjatoslav.sixth.data.store.file;
  10
  11 import java.io.IOException;
  12
  13 public class MetaData {
  14
  15     public static final int FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START = 4 * 6;
  16     private static final int FORMAT_VERSION = 1;
  17     private static final int FILE_LOCATION_VERSION = 4 * 0;
  18     private static final int FILE_LOCATION_ENTRIES_TABLE_SIZE = 4 * 1;
  19     private static final int FILE_LOCATION_USED_ENTRIES_COUNT = 4 * 2;
  20     private static final int FILE_LOCATION_CURRENT_ENTRY = 4 * 3;
  21     private static final int FILE_LOCATION_CURRENT_LOCATION = 4 * 4; // LONG!!
  22     private final FileDataStore dataStore;
  23     private int entriesTableSize;
  24     private int currentEntry;
  25     private int usedEntriesCount;
  26     private long currentLocation;
  27
  28     public MetaData(final FileDataStore dataStore) {
  29         this.dataStore = dataStore;
  30     }
  31
  32     /**
  33      * @return address of the start of the allocated space
  34      */
  35     public synchronized long allocateStorageSpace(final int amountOfBytes) {
  36         final long locationStart = currentLocation;
  37         currentLocation += amountOfBytes;
  38         return locationStart;
  39     }
  40
  41     public void decreaseUsedEntriesCount() {
  42         usedEntriesCount--;
  43     }
  44
  45     public synchronized void ensureMinimumCurrentLocation(
  46             final long minimumLocation) {
  47
  48         if (currentLocation < minimumLocation)
  49             currentLocation = minimumLocation;
  50     }
  51
  52     public boolean entriesTableNeedsIncreasing() {
  53         final int reserveSize = (entriesTableSize / 10) + 1;
  54
  55         return usedEntriesCount >= (entriesTableSize - reserveSize);
  56
  57     }
  58
  59     public long getEntriesStorageAreaStart() {
  60         return FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START
  61                 + (EntryRecord.ENTRY_RECORD_LENGTH * entriesTableSize);
  62     }
  63
  64     public long getEntriesStorageAreaStart(
  65             final int hypotheticalEntriesTableSize) {
  66         return FILE_LOCATION_ENTRY_ALLOCATION_TABLE_START
  67                 + (EntryRecord.ENTRY_RECORD_LENGTH * hypotheticalEntriesTableSize);
  68     }
  69
  70     /**
  71      * @return amount of entries in the entries table
  72      */
  73     public int getEntriesTableSize() {
  74         return entriesTableSize;
  75     }
  76
  77     public void setEntriesTableSize(final int newSize) {
  78         entriesTableSize = newSize;
  79     }
  80
  81     public int getNewEntryId() {
  82         currentEntry++;
  83
  84         if (currentEntry >= getEntriesTableSize())
  85             currentEntry = 0;
  86
  87         return currentEntry;
  88     }
  89
  90     public void increaseUsedEntriesCount() {
  91         usedEntriesCount++;
  92     }
  93
  94     public void initializeNewFile() throws IOException {
  95         entriesTableSize = 16;
  96         usedEntriesCount = 0;
  97         currentEntry = entriesTableSize - 1;
  98         currentLocation = getEntriesStorageAreaStart();
  99
 100         writeFileHeader();
 101     }
 102
 103     public void readFileHeader() throws IOException {
 104
 105         final int fileVersion = dataStore.readInt(FILE_LOCATION_VERSION);
 106         if (fileVersion != FORMAT_VERSION)
 107             throw new RuntimeException("File version is " + fileVersion
 108                     + " but version " + FORMAT_VERSION + " is required.");
 109
 110         entriesTableSize = dataStore.readInt(FILE_LOCATION_ENTRIES_TABLE_SIZE);
 111
 112         usedEntriesCount = dataStore.readInt(FILE_LOCATION_USED_ENTRIES_COUNT);
 113
 114         currentEntry = dataStore.readInt(FILE_LOCATION_CURRENT_ENTRY);
 115
 116         currentLocation = dataStore.readLong(FILE_LOCATION_CURRENT_LOCATION);
 117     }
 118
 119     public void setCurrentLocation(final long currentLocation) {
 120         this.currentLocation = currentLocation;
 121     }
 122
 123     public void writeFileHeader() throws IOException {
 124         dataStore.writeInt(FILE_LOCATION_VERSION, FORMAT_VERSION);
 125         dataStore.writeInt(FILE_LOCATION_ENTRIES_TABLE_SIZE,
 126                 getEntriesTableSize());
 127         dataStore.writeInt(FILE_LOCATION_USED_ENTRIES_COUNT, usedEntriesCount);
 128         dataStore.writeInt(FILE_LOCATION_CURRENT_ENTRY, currentEntry);
 129         dataStore.writeLong(FILE_LOCATION_CURRENT_LOCATION, currentLocation);
 130     }
 131
 132 }