Oracle® Coherence Java API Reference
v3.5.3

E15583-01

com.tangosol.net.cache
Class CachingMap

java.lang.Object
  extended by com.tangosol.net.cache.CachingMap
All Implemented Interfaces:
java.util.Map
Direct Known Subclasses:
NearCache

public class CachingMap
extends java.lang.Object
implements java.util.Map

Map implementation that wraps two maps - a front map (assumed to be "inexpensive" and probably "incomplete") and a back map (assumed to be "complete" and "correct", but more "expensive") - using a read-through/write-through approach.

If the back map implements ObservableMap interface, the CachingMap provides four different strategies of invalidating the front map entries that have changed by other processes in the back map:

The front map implementation is assumed to be thread safe; additionally any modifications to the front map are allowed only after the corresponding lock is acquired against the ControlMap.

Note: null values are not cached in the front map and therefore this implementation is not optimized for maps that allow null values to be stored.

Author:
ag/gg 2002.09.10, gg 2003.10.16

Nested Class Summary
protected  class CachingMap.BackMapListener
          MapListener for back map responsible for keeping the front map coherent with the back map.
protected  class CachingMap.FrontMapListener
          MapListener for front map responsible for deregistering back map listeners upon front map eviction.
 
Nested classes/interfaces inherited from interface java.util.Map
java.util.Map.Entry
 
Field Summary
static int LISTEN_ALL
          Invalidation strategy that instructs the CachingMap to listen to all back map events; this strategy is preferred when updates to the back map are frequent and with high probability come from the outside of this CachingMap; for example multiple CachingMap instances using the same back map with a large degree of key set overlap between front maps.
static int LISTEN_AUTO
          Invalidation strategy that instructs the CachingMap implementation to switch automatically between LISTEN_PRESENT and LISTEN_ALL strategies based on the cache statistics.
static int LISTEN_NONE
          No invalidation strategy.
static int LISTEN_PRESENT
          Invalidation strategy that instructs the CachingMap to listen to the back map events related only to the items currently present in the front map; this strategy serves best when the changes to the back map come mostly from the CachingMap itself.
protected  int m_nStrategyCurrent
          The current invalidation strategy, which at times could be different from the target strategy.
protected  int m_nStrategyTarget
          The invalidation strategy that this map is to use.
 
Constructor Summary
CachingMap(java.util.Map mapFront, java.util.Map mapBack)
          Construct a CachingMap using two specified maps: FrontMap (aka "cache", "near" or "shallow") and BackMap (aka "actual", "real" or "deep").
CachingMap(java.util.Map mapFront, java.util.Map mapBack, int nStrategy)
          Construct a CachingMap using two specified maps: FrontMap (aka "cache", "near" or "shallow") and BackMap (aka "actual", "real" or "deep") and using the specified front map invalidation strategy.
 
Method Summary
 void clear()
          Clears both the front and back maps.
 boolean containsKey(java.lang.Object oKey)
          Check whether or not this map contains a mapping for the specified key.
 boolean containsValue(java.lang.Object oValue)
          Check whether or not this CachingMap maps one or more keys to the specified value.
protected  int ensureInvalidationStrategy()
          Ensure that a strategy has been choosen and that any appropriate global listeners have been registered.
 java.util.Set entrySet()
          Obtain an set view of the mappings contained in this map.
 java.lang.Object get(java.lang.Object oKey)
          Obtain the value to which this map maps the specified key.
 java.util.Map getAll(java.util.Collection colKeys)
          Get all the specified keys, if they are in the cache.
 java.util.Map getBackMap()
          Obtain the back map reference.
 CacheStatistics getCacheStatistics()
          Obtain the CacheStatistics for this cache.
 ConcurrentMap getControlMap()
          Obtain the ConcurrentMap that should be used to synchronize the front map modification access.
 java.util.Map getFrontMap()
          Obtain the front map reference.
 long getInvalidationHits()
          Determine the rough number of front map invalidation hits since the cache statistics were last reset.
 long getInvalidationMisses()
          Determine the rough number of front map invalidation misses since the cache statistics were last reset.
 int getInvalidationStrategy()
          Obtain the invalidation strategy used by this CachingMap.
 long getTotalRegisterListener()
          Determine the total number of registerListener(Object oKey) operations since the cache statistics were last reset.
protected  MapListener instantiateBackMapListener()
          Factory pattern: instantiate back map listener.
protected  CachingMap.FrontMapListener instantiateFrontMapListener()
          Factory pattern: instantiate front map listener.
protected  void invalidateFront(java.lang.Object oKey)
          Invalidate the key from the front.
protected  boolean isCoherent()
          Determine if changes to the back map affect the front map so that data in the front map stays in sync.
 boolean isEmpty()
          Check whether or not this map is empty.
 java.util.Set keySet()
          Obtain an set view of the keys contained in this map.
 java.lang.Object put(java.lang.Object oKey, java.lang.Object oValue)
          Associates the specified value with the specified key in this map.
 java.lang.Object put(java.lang.Object oKey, java.lang.Object oValue, boolean fReturn, long cMillis)
          Implementation of put method that optionally skips the return value retrieval and allows to specify an expiry for the cache entry.
 void putAll(java.util.Map map)
          Copy all of the mappings from the specified map to this map.
protected  void registerFrontListener()
          Register the global front map listener.
protected  void registerListener()
          Register the global back map listener.
protected  void registerListener(java.lang.Object oKey)
          Register the back map listener for the specified key.
 void release()
          Release the CachingMap.
 java.lang.Object remove(java.lang.Object oKey)
          Remove the mapping for this key from this map if present.
protected  void resetInvalidationStrategy()
          Reset the "current invalidation strategy" flag.
 int size()
          Return the number of key-value mappings in this map.
 java.lang.String toString()
          For debugging purposes, format the contents of the CachingMap in a human readable format.
protected  void unregisterFrontListener()
          Unregister the global front map listener.
protected  void unregisterListener()
          Unregister the global back map listener.
protected  void unregisterListener(java.lang.Object oKey)
          Unregister the back map listener for the specified key.
protected  void validate(MapEvent evt)
          Validate the front map entry for the specified back map event.
 java.util.Collection values()
          Obtain an collection of the values contained in this map.
 
Methods inherited from interface java.util.Map
equals, hashCode
 

Field Detail

LISTEN_NONE

public static final int LISTEN_NONE
No invalidation strategy.

See Also:
Constant Field Values

LISTEN_PRESENT

public static final int LISTEN_PRESENT
Invalidation strategy that instructs the CachingMap to listen to the back map events related only to the items currently present in the front map; this strategy serves best when the changes to the back map come mostly from the CachingMap itself.

See Also:
Constant Field Values

LISTEN_ALL

public static final int LISTEN_ALL
Invalidation strategy that instructs the CachingMap to listen to all back map events; this strategy is preferred when updates to the back map are frequent and with high probability come from the outside of this CachingMap; for example multiple CachingMap instances using the same back map with a large degree of key set overlap between front maps.

See Also:
Constant Field Values

LISTEN_AUTO

public static final int LISTEN_AUTO
Invalidation strategy that instructs the CachingMap implementation to switch automatically between LISTEN_PRESENT and LISTEN_ALL strategies based on the cache statistics.

See Also:
Constant Field Values

m_nStrategyTarget

protected int m_nStrategyTarget
The invalidation strategy that this map is to use.


m_nStrategyCurrent

protected int m_nStrategyCurrent
The current invalidation strategy, which at times could be different from the target strategy.

Constructor Detail

CachingMap

public CachingMap(java.util.Map mapFront,
                  java.util.Map mapBack)
Construct a CachingMap using two specified maps: If the BackMap implements the ObservableMap interface a listener will be added to the BackMap to invalidate FrontMap items updated [externally] in the back map using the LISTEN_AUTO strategy.

Parameters:
mapBack - back map
mapFront - front map
See Also:
SeppukuMapListener

CachingMap

public CachingMap(java.util.Map mapFront,
                  java.util.Map mapBack,
                  int nStrategy)
Construct a CachingMap using two specified maps: and using the specified front map invalidation strategy.

Parameters:
mapFront - front map
mapBack - back map
nStrategy - specifies the strategy used for the front map invalidation; valid values are LISTEN_* constants
Since:
Coherence 2.3
Method Detail

release

public void release()
Release the CachingMap. If the BackMap implements an ObservableMap calling this method is necessary to remove the BackMap listener. Any access to the CachingMap which has been released will cause IllegalStateException.


getFrontMap

public java.util.Map getFrontMap()
Obtain the front map reference.

Note: direct modifications of the returned map may cause an unpredictable behavior of the CachingMap.

Returns:
the front Map

getBackMap

public java.util.Map getBackMap()
Obtain the back map reference.

Note: direct modifications of the returned map may cause an unpredictable behavior of the CachingMap.

Returns:
the back Map

getInvalidationStrategy

public int getInvalidationStrategy()
Obtain the invalidation strategy used by this CachingMap.

Returns:
one of LISTEN_* values

getControlMap

public ConcurrentMap getControlMap()
Obtain the ConcurrentMap that should be used to synchronize the front map modification access.

Returns:
a ConcurrentMap controlling the front map modifications

isCoherent

protected boolean isCoherent()
Determine if changes to the back map affect the front map so that data in the front map stays in sync.

Returns:
true if the front map has a means to stay in sync with the back map so that it does not contain stale data

getCacheStatistics

public CacheStatistics getCacheStatistics()
Obtain the CacheStatistics for this cache.

Returns:
a CacheStatistics object

clear

public void clear()
Clears both the front and back maps.

Specified by:
clear in interface java.util.Map

containsKey

public boolean containsKey(java.lang.Object oKey)
Check whether or not this map contains a mapping for the specified key.

Specified by:
containsKey in interface java.util.Map
Returns:
true if this map contains a mapping for the specified key, false otherwise.

containsValue

public boolean containsValue(java.lang.Object oValue)
Check whether or not this CachingMap maps one or more keys to the specified value.

Specified by:
containsValue in interface java.util.Map
Returns:
true if this CachingMap maps one or more keys to the specified value, false otherwise

entrySet

public java.util.Set entrySet()
Obtain an set view of the mappings contained in this map. If there is a listener for the back map, then the set will be mutable; otherwise the returned set will be immutable. The returned set reflects the full contents of the back map.

Specified by:
entrySet in interface java.util.Map
Returns:
a set view of the mappings contained in this map.

get

public java.lang.Object get(java.lang.Object oKey)
Obtain the value to which this map maps the specified key.

Specified by:
get in interface java.util.Map
Parameters:
oKey - the key object
Returns:
the value to which this map maps the specified key, or null if the map contains no mapping for this key

getAll

public java.util.Map getAll(java.util.Collection colKeys)
Get all the specified keys, if they are in the cache. For each key that is in the cache, that key and its corresponding value will be placed in the map that is returned by this method. The absence of a key in the returned map indicates that it was not in the cache, which may imply (for caches that can load behind the scenes) that the requested data could not be loaded.

Note: this implementation does not differentiate between missing keys or null values stored in the back map; in both cases the returned map will not contain the corresponding entry.

Parameters:
colKeys - a collection of keys that may be in the named cache
Returns:
a Map of keys to values for the specified keys passed in col
Since:
Coherence 2.5

isEmpty

public boolean isEmpty()
Check whether or not this map is empty. Expensive: always reflects the contents of the underlying cache.

Specified by:
isEmpty in interface java.util.Map
Returns:
true if this map contains no key-value mappings.

keySet

public java.util.Set keySet()
Obtain an set view of the keys contained in this map. If there is a listener for the back map, then the set will be mutable; otherwise the returned set will be immutable. The returned set reflects the full contents of the back map.

Specified by:
keySet in interface java.util.Map
Returns:
a set view of the keys contained in this map.

put

public java.lang.Object put(java.lang.Object oKey,
                            java.lang.Object oValue)
Associates the specified value with the specified key in this map.

Specified by:
put in interface java.util.Map
Parameters:
oKey - key with which the specified value is to be associated
oValue - value to be associated with the specified key
Returns:
previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key, if the implementation supports null values.

put

public java.lang.Object put(java.lang.Object oKey,
                            java.lang.Object oValue,
                            boolean fReturn,
                            long cMillis)
Implementation of put method that optionally skips the return value retrieval and allows to specify an expiry for the cache entry.

Parameters:
oKey - the key
oValue - the value
fReturn - if true, the return value is required; otherwise the return value will be ignored
cMillis - the number of milliseconds until the cache entry will expire
Returns:
previous value (if required)
Throws:
java.lang.UnsupportedOperationException - if the requested expiry is a positive value and either the front map or the back map implementations do not support the expiration functionality
See Also:
CacheMap.put(Object oKey, Object oValue, long cMillis)

putAll

public void putAll(java.util.Map map)
Copy all of the mappings from the specified map to this map.

Specified by:
putAll in interface java.util.Map
Parameters:
map - Mappings to be stored in this map

invalidateFront

protected void invalidateFront(java.lang.Object oKey)
Invalidate the key from the front. The caller must have the key locked.

Parameters:
oKey - the key to invalidate

validate

protected void validate(MapEvent evt)
Validate the front map entry for the specified back map event.

Parameters:
evt - the MapEvent from the back map

remove

public java.lang.Object remove(java.lang.Object oKey)
Remove the mapping for this key from this map if present. Expensive: updates both the underlying cache and the local cache.

Specified by:
remove in interface java.util.Map
Parameters:
oKey - key whose mapping is to be removed from the map
Returns:
previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key, if the implementation supports null values.

size

public int size()
Return the number of key-value mappings in this map. Expensive: always reflects the contents of the underlying cache.

Specified by:
size in interface java.util.Map
Returns:
the number of key-value mappings in this map

values

public java.util.Collection values()
Obtain an collection of the values contained in this map. If there is a listener for the back map, then the collection will be mutable; otherwise the returned collection will be immutable. The returned collection reflects the full contents of the back map.

Specified by:
values in interface java.util.Map
Returns:
a collection view of the values contained in this map

getInvalidationHits

public long getInvalidationHits()
Determine the rough number of front map invalidation hits since the cache statistics were last reset.

An invalidation hit is an externally induced map event for an entry that exists in the front map.

Returns:
the number of cache invalidation hits

getInvalidationMisses

public long getInvalidationMisses()
Determine the rough number of front map invalidation misses since the cache statistics were last reset. An invalidation miss is an externally induced map event for an entry that does not exists in the front map.

Returns:
the number of cache invalidation misses

getTotalRegisterListener

public long getTotalRegisterListener()
Determine the total number of registerListener(Object oKey) operations since the cache statistics were last reset.

Returns:
the total number of listener registrations

toString

public java.lang.String toString()
For debugging purposes, format the contents of the CachingMap in a human readable format.

Returns:
a String representation of the CachingMap object

registerListener

protected void registerListener()
Register the global back map listener.


unregisterListener

protected void unregisterListener()
Unregister the global back map listener.


registerListener

protected void registerListener(java.lang.Object oKey)
Register the back map listener for the specified key.

Parameters:
oKey - the key

unregisterListener

protected void unregisterListener(java.lang.Object oKey)
Unregister the back map listener for the specified key.

Parameters:
oKey - the key

registerFrontListener

protected void registerFrontListener()
Register the global front map listener.


unregisterFrontListener

protected void unregisterFrontListener()
Unregister the global front map listener.


ensureInvalidationStrategy

protected int ensureInvalidationStrategy()
Ensure that a strategy has been choosen and that any appropriate global listeners have been registered.

Returns:
the current strategy

resetInvalidationStrategy

protected void resetInvalidationStrategy()
Reset the "current invalidation strategy" flag.

This method should be called only while the access to the front map is fully synchronzied and the front map is empty to prevent stalled data.


instantiateBackMapListener

protected MapListener instantiateBackMapListener()
Factory pattern: instantiate back map listener.

Returns:
an instance of back map listener responsible for keeping the front map coherent with the back map

instantiateFrontMapListener

protected CachingMap.FrontMapListener instantiateFrontMapListener()
Factory pattern: instantiate front map listener.

Returns:
an instance of front map listener

Oracle® Coherence Java API Reference
v3.5.3

E15583-01

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