Class ChiseledMap

src/main/java/org/sfj/ChiseledMap.java:67–625

Dead simple persistent ordered map. It is thread safe, via coarse synchronization on writes. Reads are unsynchronized, though the underlying FileChannel is shared. Deletes do not reclaim file space; they simply stop referencing the block. Writes are CRC checked on restart, file is truncated to ma

 * @author cschanck
 */
public class ChiseledMap<K, V> extends AbstractMap<K, V> implements ConcurrentMap<K, V> {

  public static final int DIGEST_MASK = 0x7fffffff;

  public static final byte[] HDR = "(-:AnonymousBC:ChiseledMap-)".getBytes(StandardCharsets.US_ASCII);

  /**
   * Open methods.
   */
  public enum OpenOption {
    MUST_BE_NEW, MUST_EXIST, DONT_CARE
  }

  /**
   * For the map methods, IOExceptions are wrapped in this.
   */
  public static class RuntimeIOException extends RuntimeException {
    public RuntimeIOException(Throwable cause) {
      super(cause);
    }
  }

  /**
   * Encode a key/value (here you must handle null values) into a ByteBuffer.
   * @param <KK> key type
   * @param <VV> value type
   */
  @FunctionalInterface
  public interface Encoder<KK, VV> {
    ByteBuffer encode(KK k, VV v) throws IOException;
  }

  /**
   * Decode a byte array into a key/value pair.
   * @param <KK> key type
   * @param <VV> value type
   */
  @FunctionalInterface
  public interface Decoder<KK, VV> {
    Entry<KK, VV> decode(byte[] bArray) throws IOException;
  }

  private final CRC32 digest;
  private final Comparator<K> comp;
  private final FileChannel fc;
  private final ConcurrentSkipListMap<K, Long> map;
  private final ByteBuffer lenBuffer = ByteBuffer.allocate(4);
  private final ByteBuffer digestBuffer = ByteBuffer.allocate(4);
  private final ByteBuffer writeBuffer = ByteBuffer.allocateDirect(1024 * 1024);
  private final File file;
  private long currentWritePos = HDR.length;
  private long nextWritePos = HDR.length;
  private volatile int pendingWrites = 0;
  private final Encoder<K, V> encoder;
  private final Decoder<K, V> decoder;
  private long entriesOnDisk = 0;

  /**