com.aoindustries.util.persistent

Class PersistentCollections

java.lang.Object

com.aoindustries.util.persistent.PersistentCollections

public class PersistentCollections
extends Object

A set of static utility methods to help in the selection, creation, and management of persistent collections.

Author:

AO Industries, Inc.

Method Summary

Modifier and Type	Method and Description
static boolean	ensureZeros(ByteBuffer byteBuffer, int position, int count) Stores the requested number of zeros to the provided ByteBuffer, but only if they do not already contain zeros.
static boolean	ensureZeros(RandomAccessFile raf, long position, long count) Writes the requested number of zeros to the provided RandomAccessFile, but only if they do not already contain zeros.
static PersistentBlockBuffer	getPersistentBlockBuffer(Serializer<?> serializer, PersistentBuffer pbuffer, long additionalBlockSpace) Gets the most efficient PersistentBlockBuffer for the provided provided Serializer.
static PersistentBuffer	getPersistentBuffer(long maximumCapacity) Selects the most efficient temporary PersistentBuffer for the current machine and the provided maximum buffer size.
static PersistentBuffer	getPersistentBuffer(RandomAccessFile raf, ProtectionLevel protectionLevel, long maximumCapacity) Selects the most efficient PersistentBuffer for the current machine and the provided maximum buffer size.
static <E> Serializer<E>	getSerializer(Class<E> type) Selects the most efficient Serializer for the provided class.

Methods inherited from class java.lang.Object

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

Method Detail

ensureZeros

public static boolean ensureZeros(RandomAccessFile raf,
                                  long position,
                                  long count)
                           throws IOException

Writes the requested number of zeros to the provided RandomAccessFile, but only if they do not already contain zeros. This is to avoid unnecessary writes on flash media. This may also have a positive interaction with sparse files.

Returns:

true when the byteBuffer was written to

Throws:

IOException

ensureZeros

public static boolean ensureZeros(ByteBuffer byteBuffer,
                                  int position,
                                  int count)
                           throws IOException

Stores the requested number of zeros to the provided ByteBuffer, but only if they do not already contain zeros. This is to avoid unnecessary writes on flash media. This may also have a positive interaction with sparse files.

Returns:

true when the byteBuffer was written to

Throws:

IOException

getPersistentBuffer

public static PersistentBuffer getPersistentBuffer(long maximumCapacity)
                                            throws IOException

Selects the most efficient temporary PersistentBuffer for the current machine and the provided maximum buffer size. The buffer will be backed by a temporary file that will be deleted on buffer close or JVM shutdown. The protection level will be NONE. The order of preference is:

1. MappedPersistentBuffer
2. LargeMappedPersistentBuffer
3. RandomAccessFileBuffer

Parameters:

maximumCapacity - The maximum size of data that may be stored in the buffer. To ensure no limits, use Long.MAX_VALUE.

Throws:

IOException

getPersistentBuffer

public static PersistentBuffer getPersistentBuffer(RandomAccessFile raf,
                                                   ProtectionLevel protectionLevel,
                                                   long maximumCapacity)
                                            throws IOException

Selects the most efficient PersistentBuffer for the current machine and the provided maximum buffer size. The order of preference is:

1. MappedPersistentBuffer
2. LargeMappedPersistentBuffer
3. RandomAccessFileBuffer

Parameters:

maximumCapacity - The maximum size of data that may be stored in the buffer. If the random access file is larger than this value, the length of the file is used instead. To ensure no limits, use Long.MAX_VALUE.

Throws:

IOException

getSerializer

public static <E> Serializer<E> getSerializer(Class<E> type)

Selects the most efficient Serializer for the provided class.

getPersistentBlockBuffer

public static PersistentBlockBuffer getPersistentBlockBuffer(Serializer<?> serializer,
                                                             PersistentBuffer pbuffer,
                                                             long additionalBlockSpace)
                                                      throws IOException

Gets the most efficient PersistentBlockBuffer for the provided provided Serializer. If using fixed record sizes, the size of the block buffer is rounded up to the nearest power of two, to help alignment with system page tables.

Parameters:

serializer - The Serializer that will be used to write to the blocks

pbuffer - The PersistenceBuffer that will be wrapped by the block buffer

additionalBlockSpace - The maximum additional space needed beyond the space used by the serializer. This may be used for linked list pointers, for example.

Throws:

IOException