ch.javasoft.jbase
Class BufferedRandomAccessPersister

java.lang.Object
  ch.javasoft.jbase.BufferedRandomAccessPersister

All Implemented Interfaces:

Stateful, RandomAccessPersister

public class BufferedRandomAccessPersister
extends Object
implements RandomAccessPersister

The BufferedRandomAccessPersister caches data in a hash table, and delegates the real i/o operations to an underlying delegate RandomAccessPersister.

Note that all cache-access is thread safe. If the caller guarantees that atomic read and write operations do not overlap, the class is thread-safe, even if concurrent read operations are overlapping.

Constructor Summary

BufferedRandomAccessPersister(File file, int tableSize, int entrySize)
Constructor using a RandomAccessFilePersistor as delegate, and a cache acording to the specified specifications.

BufferedRandomAccessPersister(RandomAccessPersister delegate, int tableSize, int entrySize)
Constructor with delegate persistor and cache specifications.

Method Summary

void	close(boolean erase) Closes this persistor, subsequent read or write calls will cause an exception.
RandomAccessPersister	createReadCopy(ReadWriteLock lock) Override to specialize return type
void	flush() Ensures that any possibly cached data is written to the underlying store
protected void	flushDirtyEntry(RandomAccessPersister delegate, ch.javasoft.jbase.BufferedRandomAccessPersister.TableEntry entry) PRECONDITION: read or write lock held
DataInput	getInput() Returns a data input object to read from.
DataOutput	getOutput() Returns a data input object to write to.
long	getPosition() Returns the current byte position.
void	setLength(long byteLength) Sets the length of the storage.
void	setPosition(long bytePos) Sets the byte offset position.

Methods inherited from class java.lang.Object

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

Constructor Detail

BufferedRandomAccessPersister

public BufferedRandomAccessPersister(File file,
                                     int tableSize,
                                     int entrySize)
                              throws FileNotFoundException

Constructor using a RandomAccessFilePersistor as delegate, and a cache acording to the specified specifications.

Notes:

• the maximum cache size is tableSize * entrySize
• larger tableSize has positive influence on all functions, but especially random read access can profit
• larger entrySize has positive influence for sequential write operations, but might have negative affect in combination with small tableSize and random modifying operations

Recommended values:

• tableSize = 64, entrySize = 256: good setting for general purpose use, maximum cache size is 16K
• tableSize = 256, entrySize = 64: faster read operations, on the price of slower writing, maximum cache size is 16K

Parameters:

file - file to create a RandomAccessFilePersistor

tableSize - number of entries in the hash table

entrySize - buffer byte length of a single hash table entry

Throws:

FileNotFoundException - if the specified file is not found

BufferedRandomAccessPersister

public BufferedRandomAccessPersister(RandomAccessPersister delegate,
                                     int tableSize,
                                     int entrySize)

Constructor with delegate persistor and cache specifications.

Notes:

• the maximum cache size is tableSize * entrySize
• larger tableSize has positive influence on all functions, but especially random read access can profit
• larger entrySize has positive influence for sequential write operations, but might have negative affect in combination with small tableSize and random modifying operations

Recommended values:

• tableSize = 64, entrySize = 256: good setting for general purpose use, maximum cache size is 16K
• tableSize = 256, entrySize = 64: faster read operations, on the price of slower writing, maximum cache size is 16K

Parameters:

delegate - delegate persistor, does the real i/o operations

tableSize - number of entries in the hash table

entrySize - buffer byte length of a single hash table entry

Method Detail

getInput

public DataInput getInput()
                   throws IOException

Description copied from interface: RandomAccessPersister

Returns a data input object to read from. Read operations increment the current byte position

Specified by:

getInput in interface RandomAccessPersister

Throws:

IOException

getOutput

public DataOutput getOutput()
                     throws IOException

Description copied from interface: RandomAccessPersister

Returns a data input object to write to. Write operations increment the current byte position

Specified by:

getOutput in interface RandomAccessPersister

Throws:

IOException

getPosition

public long getPosition()
                 throws IOException

Description copied from interface: RandomAccessPersister

Returns the current byte position. Note that any read or write operation increments the position.

Specified by:

getPosition in interface RandomAccessPersister

Throws:

IOException

setPosition

public void setPosition(long bytePos)
                 throws IOException

Description copied from interface: RandomAccessPersister

Sets the byte offset position. Subsequent read or write operations start at the specified position, even if it is after the actual length of the file or store. However, the length does not change before actually writing at this position.

Specified by:

setPosition in interface RandomAccessPersister

Throws:

IOException

setLength

public void setLength(long byteLength)
               throws IOException

Description copied from interface: RandomAccessPersister

Sets the length of the storage. If this is shorter than the current length, the data will be truncated. If it is after the current length, additional data is appended, but its content is undefined.

Specified by:

setLength in interface RandomAccessPersister

Throws:

IOException

flush

public void flush()
           throws IOException

Description copied from interface: RandomAccessPersister

Ensures that any possibly cached data is written to the underlying store

Specified by:

flush in interface RandomAccessPersister

Throws:

IOException

flushDirtyEntry

protected void flushDirtyEntry(RandomAccessPersister delegate,
                               ch.javasoft.jbase.BufferedRandomAccessPersister.TableEntry entry)
                        throws IOException

PRECONDITION: read or write lock held

Throws:

IOException

close

public void close(boolean erase)
           throws IOException

Description copied from interface: RandomAccessPersister

Closes this persistor, subsequent read or write calls will cause an exception. Multiple close calls, however, do not cause any exceptions.

Specified by:

close in interface RandomAccessPersister

Parameters:

erase - if true, underlying files are deleted upon close

Throws:

IOException

createReadCopy

public RandomAccessPersister createReadCopy(ReadWriteLock lock)
                                     throws IOException

Description copied from interface: RandomAccessPersister

Override to specialize return type

Specified by:

createReadCopy in interface Stateful

Specified by:

createReadCopy in interface RandomAccessPersister

Parameters:

lock - A read/write lock, the write lock is held. The lock, however, might also be used for other functionality of the returned read copy, for instance, if the read copy has to be put in sync with the main object.

Returns:

a new read copy instance, with copied state compared to other read copy instances

Throws:

IOException

See Also:

Stateful.createReadCopy(ReadWriteLock)