com.faunos.skwish.sys.mgr
Class FileBackedDeleteSet

java.lang.Object
  com.faunos.skwish.sys.filters.DeleteSet
      com.faunos.skwish.sys.mgr.FileBackedDeleteSet

All Implemented Interfaces:

Closeable

public class FileBackedDeleteSet
extends DeleteSet
implements Closeable

A DeleteSet that is backed by a file. The file format used is super brittle.

File Format

The backing file consists of a list of fixed-width, 8 byte longs representing the list of deleted [entry] IDs. The file's byte size (size / 8 - 2) determines the number deleted IDs. Thus the file size is always a multiple of 8. The list of deleted IDs is not ordered; however, the deleted IDs are unique (i.e., non-repeating).

Layout

      DELETED_ID_LIST := MIN_ID, MAX_ID, <DELETED_ID> n = 0, 1, 2, ..
      MIN_ID := LONG
      MAX_ID := LONG
      DELETED_ID := LONG
      LONG := <BYTE>8
 

Notes:

The implementation does not require that the IDs be unique. (A list containing duplicate entry IDs does not cause loadInstance(FileChannel) to fail.) However, the implementation never produces duplicates, either.

The implementation is not safe for concurrent access. In particular, the backing FileChannel's position is assumed to be owned by the instance.

Author:

Babak Farhang

Field Summary

protected static ChannelUtil<DeleteSetException>

helper

Fields inherited from class com.faunos.skwish.sys.filters.DeleteSet

deletedIds, validator

Constructor Summary

protected

FileBackedDeleteSet(FileChannel deletedIdsFile, long minId, long maxId) Used internally and by subclasses.

Method Summary

void	close()
boolean	delete(long id) Adds the given id to the delete-set.
void	flush()
Set<Long>	getRawDeletedIds()
boolean	include(DeleteSet other) Operation not supported.
boolean	isIncludeSupported() Determines whether the instance supports the include method.
static FileBackedDeleteSet	loadInstance(FileChannel deletedIdsFile) Loads and returns an already existing instance from the given backing file.
static FileBackedDeleteSet	writeNewInstance(FileChannel deletedIdsFile, long minId, long maxId) Writes a new, empty deleted ID list to the given backing file and returns a new instance of this class.

Methods inherited from class com.faunos.skwish.sys.filters.DeleteSet

combine, getCount, getDeletedIds, getMaxId, getMinId, initSet, inRange, isDeleted, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

helper

protected static final ChannelUtil<DeleteSetException> helper

Constructor Detail

FileBackedDeleteSet

protected FileBackedDeleteSet(FileChannel deletedIdsFile,
                              long minId,
                              long maxId)

Used internally and by subclasses.

See Also:

loadInstance(FileChannel), writeNewInstance(FileChannel, long, long)

Method Detail

loadInstance

public static FileBackedDeleteSet loadInstance(FileChannel deletedIdsFile)
                                        throws IOException

Loads and returns an already existing instance from the given backing file. The specified file must be positioned at the start of the list (which need not be zero).

Throws:

IOException

writeNewInstance

public static FileBackedDeleteSet writeNewInstance(FileChannel deletedIdsFile,
                                                   long minId,
                                                   long maxId)
                                            throws IOException

Writes a new, empty deleted ID list to the given backing file and returns a new instance of this class. The file must be positioned at the start of the list (which need not be the same thing as the start of the file). On return, the file size will be truncated in order to reflect an empty deleted ID list.

Throws:

IOException

delete

public boolean delete(long id)
               throws IOException

Description copied from class: DeleteSet

Adds the given id to the delete-set.

Overrides:

delete in class DeleteSet

Parameters:

id - the ID to be deleted, which lie in this delete-set's range

Returns:

true, if the specified id wasn't already deleted; false, o.w.

Throws:

IOException

include

public boolean include(DeleteSet other)
                throws IOException,
                       UnsupportedOperationException

Operation not supported.

Overrides:

include in class DeleteSet

Throws:

UnsupportedOperationException

IOException

isIncludeSupported

public boolean isIncludeSupported()

Description copied from class: DeleteSet

Determines whether the instance supports the include method.

Overrides:

isIncludeSupported in class DeleteSet

Returns:

false

close

public void close()
           throws IOException

Specified by:

close in interface Closeable

Throws:

IOException

flush

public void flush()
           throws IOException

Throws:

IOException

getRawDeletedIds

public Set<Long> getRawDeletedIds()