org.cache2k.storage

Class ImageFileStorage

java.lang.Object

org.cache2k.storage.ImageFileStorage

All Implemented Interfaces:

CacheStorage, EntryExpiryUpdateableStorage, FlushableStorage

public class ImageFileStorage
extends Object
implements CacheStorage, FlushableStorage, EntryExpiryUpdateableStorage

Implements a robust storage on a file or a byte buffer.

The storage tries to be robust and does not require a clean shutdown, so it will survive machine crashes. In this case it uses the latest data possible that is known to be intact. The amount of data loss can be controlled by specifying a commit interval.

Possible optimizations: More specialized data structures, compaction.

Author:

Jens Wilke; created: 2014-03-27

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ImageFileStorage.Provider
static class	ImageFileStorage.SlotBucket
static class	ImageFileStorage.Tunable Some parameters factored out, which may be modified if needed.

Nested classes/interfaces inherited from interface org.cache2k.storage.FlushableStorage

FlushableStorage.FlushContext

Nested classes/interfaces inherited from interface org.cache2k.storage.CacheStorage

CacheStorage.EntryFilter, CacheStorage.EntryVisitor, CacheStorage.MultiThreadedContext, CacheStorage.VisitContext

Field Summary

Fields

Modifier and Type	Field and Description
FreeSpaceMap	freeMap

Constructor Summary

Constructors

Constructor and Description
ImageFileStorage()
ImageFileStorage(ImageFileStorage.Tunable t)

Method Summary

Methods

Modifier and Type	Method and Description
static int	calculateCompressedLongSize(long v)
void	clear() Remove the files.
void	close() Free all resources and stop operations immediately.
boolean	contains(Object key) Returns true if there is a mapping for the key.
void	fastClose() Close immediately without doing a commit.
void	flush(FlushableStorage.FlushContext ctx, long now) Write key to object index to disk for all modified entries.
StorageEntry	get(Object key) Retrieve the entry from the storage.
int	getEntryCount()
long	getFreeSpace()
long	getPutCnt()
long	getTotalValueSpace()
int	getUncommittedEntryCount()
boolean	isClosed()
boolean	isDataLost() Flag if there was a problem at the last startup and probably some data was lost.
void	open(CacheStorageContext ctx, StorageConfiguration cfg)
void	put(StorageEntry e) Store a new entry.
static long	readCompressedLong(ByteBuffer b)
boolean	remove(Object key)
String	toString() Prints out current state.
void	updateEntryExpireTime(Object key, long _millis) Update the expiry time of a stored entry.
void	visit(CacheStorage.VisitContext ctx, CacheStorage.EntryFilter f, CacheStorage.EntryVisitor v) Iterate over all stored entries and call the entry visitor.
static void	writeCompressedLong(ByteBuffer b, long v) Write a long as multiple short values.

Methods inherited from class java.lang.Object

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

Field Detail

freeMap

public final FreeSpaceMap freeMap

Constructor Detail

ImageFileStorage

public ImageFileStorage(ImageFileStorage.Tunable t)
                 throws IOException,
                        ClassNotFoundException

Throws:

IOException

ClassNotFoundException

ImageFileStorage

public ImageFileStorage()

Method Detail

open

public void open(CacheStorageContext ctx,
        StorageConfiguration cfg)
          throws IOException

Throws:

IOException

close

public void close()
           throws Exception

Description copied from interface: CacheStorage

Free all resources and stop operations immediately.

Specified by:

close in interface CacheStorage

Throws:

Exception

clear

public void clear()
           throws IOException

Remove the files. We do no synchronize here, since cache guarantees we are alone.

Specified by:

clear in interface CacheStorage

Throws:

IOException

fastClose

public void fastClose()
               throws IOException

Close immediately without doing a commit.

Throws:

IOException

get

public StorageEntry get(Object key)
                 throws IOException,
                        ClassNotFoundException

Description copied from interface: CacheStorage

Retrieve the entry from the storage. If there is no mapping for the key, null is returned.

Depending on the cache configuration, an exception on get is not severe. The cache will try other sources or return null.

Specified by:

get in interface CacheStorage

Throws:

IOException

ClassNotFoundException

contains

public boolean contains(Object key)
                 throws IOException

Description copied from interface: CacheStorage

Returns true if there is a mapping for the key.

An exception on contains is not severe. The cache will try other sources or return null.

Specified by:

contains in interface CacheStorage

Throws:

IOException

remove

public boolean remove(Object key)
               throws IOException,
                      ClassNotFoundException

Specified by:

remove in interface CacheStorage

Throws:

IOException

ClassNotFoundException

put

public void put(StorageEntry e)
         throws IOException,
                ClassNotFoundException

Store a new entry. To achieve robustness without implementing a WAL there is no update in place. Each entry gets a newly allocated space. The freed space will be made available later in time.

Parallel reads on the same storage entry still read on the now freed space. This is okay since the space will be reallocated later in time. There is no real protection against a put and get race. However, we only get in trouble if the get will need several seconds to finish.

Specified by:

put in interface CacheStorage

Throws:

IOException - may be thrown if hope is lost

ClassNotFoundException

getEntryCount

public int getEntryCount()

Specified by:

getEntryCount in interface CacheStorage

getFreeSpace

public long getFreeSpace()

getTotalValueSpace

public long getTotalValueSpace()

getUncommittedEntryCount

public int getUncommittedEntryCount()

isDataLost

public boolean isDataLost()

Flag if there was a problem at the last startup and probably some data was lost. This is an indicator for an unclean shutdown, crash, etc.

flush

public void flush(FlushableStorage.FlushContext ctx,
         long now)
           throws IOException

Write key to object index to disk for all modified entries. The implementation only works single threaded.

Specified by:

flush in interface FlushableStorage

Throws:

IOException

isClosed

public boolean isClosed()

visit

public void visit(CacheStorage.VisitContext ctx,
         CacheStorage.EntryFilter f,
         CacheStorage.EntryVisitor v)
           throws Exception

Description copied from interface: CacheStorage

Iterate over all stored entries and call the entry visitor. It is generally safe to return expired entries. If PurgeableStorage is not implemented, returning expired entries is a must, to support the generic purge algorithm.

If the ExecutorService is used, the method may return immediately without the waiting for all threads to finish. This is done by the caller, when needed.

Specified by:

visit in interface CacheStorage

Throws:

Exception

updateEntryExpireTime

public void updateEntryExpireTime(Object key,
                         long _millis)
                           throws Exception

Description copied from interface: EntryExpiryUpdateableStorage

Update the expiry time of a stored entry. If the entry is not existing, the method returns without exception.

Specified by:

updateEntryExpireTime in interface EntryExpiryUpdateableStorage

Throws:

Exception

getPutCnt

public long getPutCnt()

toString

public String toString()

Prints out current state. The output is not necessarily consistent, because no lock is used.

Overrides:

toString in class Object

readCompressedLong

public static long readCompressedLong(ByteBuffer b)

writeCompressedLong

public static void writeCompressedLong(ByteBuffer b,
                       long v)

Write a long as multiple short values. The msb in the short means that there is another short coming.

calculateCompressedLongSize

public static int calculateCompressedLongSize(long v)