Package org.hibernate.cache

Class ReadWriteCache

java.lang.Object

org.hibernate.cache.ReadWriteCache

All Implemented Interfaces:

CacheConcurrencyStrategy

public class ReadWriteCache
extends Object
implements CacheConcurrencyStrategy

Caches data that is sometimes updated while maintaining the semantics of "read committed" isolation level. If the database is set to "repeatable read", this concurrency strategy almost maintains the semantics. Repeatable read isolation is compromised in the case of concurrent writes. This is an "asynchronous" concurrency strategy.

If this strategy is used in a cluster, the underlying cache implementation must support distributed hard locks (which are held only momentarily). This strategy also assumes that the underlying cache implementation does not do asynchronous replication and that state has been fully replicated as soon as the lock is released.

See Also:

• for a faster algorithm
• CacheConcurrencyStrategy

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static final class	ReadWriteCache.Item	An item of cached data, timestamped with the time it was cached,.
static final class	ReadWriteCache.Lock	A soft lock which supports concurrent locking, timestamped with the time it was released
static interface	ReadWriteCache.Lockable

Constructor Summary

Constructors

Constructor	Description
ReadWriteCache()

Method Summary

Modifier and Type	Method	Description
boolean	afterInsert(Object key, Object value, Object version)	Add the new item to the cache, checking that no other transaction has accessed the item.
boolean	afterUpdate(Object key, Object value, Object version, SoftLock clientLock)	Re-cache the updated state, if and only if there there are no other concurrent soft locks.
void	clear()	Evict all items from the cache immediately.
void	destroy()	Clean up all resources.
void	evict(Object key)	Do nothing.
Object	get(Object key, long txTimestamp)	Do not return an item whose timestamp is later than the current transaction timestamp.
Cache	getCache()	Get the wrapped cache implementation
String	getRegionName()	Get the cache region name
boolean	insert(Object key, Object value, Object currentVersion)	Do nothing.
SoftLock	lock(Object key, Object version)	Stop any other transactions reading or writing this item to/from the cache.
boolean	put(Object key, Object value, long txTimestamp, Object version, Comparator versionComparator, boolean minimalPut)	Do not add an item to the cache unless the current transaction timestamp is later than the timestamp at which the item was invalidated.
void	release(Object key, SoftLock clientLock)	Release the soft lock on the item.
void	remove(Object key)	Evict an item from the cache immediately (without regard for transaction isolation).
void	setCache(Cache cache)	Set the underlying cache implementation.
String	toString()
boolean	update(Object key, Object value, Object currentVersion, Object previousVersion)	Do nothing.

Methods inherited from class java.lang.Object

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

Constructor Details

ReadWriteCache

public ReadWriteCache()

Method Details

setCache

public void setCache(Cache cache)

Description copied from interface: CacheConcurrencyStrategy

Set the underlying cache implementation.

Specified by:

setCache in interface CacheConcurrencyStrategy

Parameters:

cache -

getCache

public Cache getCache()

Description copied from interface: CacheConcurrencyStrategy

Get the wrapped cache implementation

Specified by:

getCache in interface CacheConcurrencyStrategy

getRegionName

public String getRegionName()

Description copied from interface: CacheConcurrencyStrategy

Get the cache region name

Specified by:

getRegionName in interface CacheConcurrencyStrategy

get

public Object get(Object key,
 long txTimestamp)
           throws CacheException

Do not return an item whose timestamp is later than the current transaction timestamp. (Otherwise we might compromise repeatable read unnecessarily.) Do not return an item which is soft-locked. Always go straight to the database instead.

Note that since reading an item from that cache does not actually go to the database, it is possible to see a kind of phantom read due to the underlying row being updated after we have read it from the cache. This would not be possible in a lock-based implementation of repeatable read isolation. It is also possible to overwrite changes made and committed by another transaction after the current transaction read the item from the cache. This problem would be caught by the update-time version-checking, if the data is versioned or timestamped.

Specified by:

get in interface CacheConcurrencyStrategy

Parameters:

key -

txTimestamp - a timestamp prior to the transaction start time

Returns:

the cached object or null

Throws:

CacheException

lock

public SoftLock lock(Object key,
 Object version)
              throws CacheException

Stop any other transactions reading or writing this item to/from the cache. Send them straight to the database instead. (The lock does time out eventually.) This implementation tracks concurrent locks of transactions which simultaneously attempt to write to an item.

Specified by:

lock in interface CacheConcurrencyStrategy

Parameters:

key -

version -

Throws:

CacheException

put

public boolean put(Object key,
 Object value,
 long txTimestamp,
 Object version,
 Comparator versionComparator,
 boolean minimalPut)
            throws CacheException

Do not add an item to the cache unless the current transaction timestamp is later than the timestamp at which the item was invalidated. (Otherwise, a stale item might be re-added if the database is operating in repeatable read isolation mode.) For versioned data, don't add the item unless it is the later version.

Specified by:

put in interface CacheConcurrencyStrategy

Parameters:

key -

value -

txTimestamp - a timestamp prior to the transaction start time

version - the item version number

versionComparator - a comparator used to compare version numbers

minimalPut - indicates that the cache should avoid a put is the item is already cached

Returns:

true if the object was successfully cached

Throws:

CacheException

release

public void release(Object key,
 SoftLock clientLock)
             throws CacheException

Release the soft lock on the item. Other transactions may now re-cache the item (assuming that no other transaction holds a simultaneous lock).

Specified by:

release in interface CacheConcurrencyStrategy

Parameters:

key -

Throws:

CacheException

clear

public void clear()
           throws CacheException

Description copied from interface: CacheConcurrencyStrategy

Evict all items from the cache immediately.

Specified by:

clear in interface CacheConcurrencyStrategy

Throws:

CacheException

remove

public void remove(Object key)
            throws CacheException

Description copied from interface: CacheConcurrencyStrategy

Evict an item from the cache immediately (without regard for transaction isolation).

Specified by:

remove in interface CacheConcurrencyStrategy

Parameters:

key -

Throws:

CacheException

destroy

public void destroy()

Description copied from interface: CacheConcurrencyStrategy

Clean up all resources.

Specified by:

destroy in interface CacheConcurrencyStrategy

afterUpdate

public boolean afterUpdate(Object key,
 Object value,
 Object version,
 SoftLock clientLock)
                    throws CacheException

Re-cache the updated state, if and only if there there are no other concurrent soft locks. Release our lock.

Specified by:

afterUpdate in interface CacheConcurrencyStrategy

Throws:

CacheException

afterInsert

public boolean afterInsert(Object key,
 Object value,
 Object version)
                    throws CacheException

Add the new item to the cache, checking that no other transaction has accessed the item.

Specified by:

afterInsert in interface CacheConcurrencyStrategy

Throws:

CacheException

evict

public void evict(Object key)
           throws CacheException

Do nothing.

Specified by:

evict in interface CacheConcurrencyStrategy

Throws:

CacheException

insert

public boolean insert(Object key,
 Object value,
 Object currentVersion)

Do nothing.

Specified by:

insert in interface CacheConcurrencyStrategy

update

public boolean update(Object key,
 Object value,
 Object currentVersion,
 Object previousVersion)

Do nothing.

Specified by:

update in interface CacheConcurrencyStrategy

toString

public String toString()

Overrides:

toString in class Object