com.tangosol.net.cache
Class SimpleOverflowMap

java.lang.Object
  com.tangosol.util.Base
      com.tangosol.util.AbstractKeyBasedMap
          com.tangosol.net.cache.SimpleOverflowMap

All Implemented Interfaces:

Map

public class SimpleOverflowMap
extends AbstractKeyBasedMap

A non-observable Map implementation that wraps two maps - a front map (assumed to be fast but limited in its maximum size) and a back map (assumed to be slower but much less limited in its maximum size).

The SimpleOverflowMap is not observable, and as such it is assumed to be a passive data structure. In other words, it does not support item expiration or other types of "self-generating" events. As such, it may be more efficient for many common use cases that would benefit from the complete avoidance of event handling. As a second effect of being a passive data structure, the implementation is able to avoid tracking all of its entries; instead it tracks only entries that are in the front map and those that currently have a pending event or an in-flight operation occurring. This means that huge key sets are possible, since only keys in the front map will be managed in memory by the overflow map, but it means that some operations that would benefit from knowing the entire set of keys will be more expensive. Examples of operations that would be less efficient as a result include containsKey(), size(), keySet().iterator(), etc.

Since:

Coherence 3.1

Author:

cp 2005.07.11

Nested Class Summary

protected static class	SimpleOverflowMap.FrontFilterConverter A combination Filter and Converter used to iterate through the status map in order to iterate through the front keys.
protected class	SimpleOverflowMap.FrontMapListener A listener for the front map that moves evictions to the back map.
protected static class	SimpleOverflowMap.HashcodeComparator A stateless Comparator that compares Object.hashCode() values.
protected class	SimpleOverflowMap.KeyIterator An Iterator implementation that attempts to provide the most resilient and most up-to-date view of the keys in the OverflowMap.
protected static class	SimpleOverflowMap.Status The Status object is used to manage concurrency at the key level for the key-level operations against the Map, to track all the items in the front Map, to manage the state transition for operations occurring against the Map, and to coordinate events across multiple threads.

Nested classes/interfaces inherited from class com.tangosol.util.AbstractKeyBasedMap

AbstractKeyBasedMap.EntrySet, AbstractKeyBasedMap.KeySet, AbstractKeyBasedMap.ValuesCollection

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry

Field Summary

static int	ENTRY_DELETED This event indicates that an entry has been removed from the map.
static int	ENTRY_INSERTED This event indicates that an entry has been added to the map.
static int	ENTRY_UPDATED This event indicates that an entry has been updated in the map.
protected Map	m_mapBack The "back" map, which the front overflows to.
protected ObservableMap	m_mapFront The "front" map, which is size-limited.
protected Map	m_mapMiss The miss cache; may be null.
protected SimpleCacheStatistics	m_stats The CacheStatistics object maintained by this cache.

Constructor Summary

SimpleOverflowMap(ObservableMap mapFront, Map mapBack)
Construct a SimpleOverflowMap using two specified maps: FrontMap (aka "cache" or "shallow") and BackMap (aka "file" or "deep")

SimpleOverflowMap(ObservableMap mapFront, Map mapBack, Map mapMiss)
Construct a SimpleOverflowMap using three specified maps: Front Map (aka "cache" or "shallow") and Back Map (aka "file" or "deep") Miss Cache

Method Summary

protected SimpleOverflowMap.Status[]	beginBulkKeyProcess(Object[] aoKey) Begin key-level procecessing for any number of keys.
protected SimpleOverflowMap.Status	beginKeyProcess(Object oKey) Block until a key is available for processing, and return the Status object for that key.
protected void	beginMapProcess() Block until this thread has exclusive access to perform operations against the OverflowMap.
void	clear() Clear all key/value mappings.
boolean	containsKey(Object oKey) Returns true if this map contains a mapping for the specified key.
protected void	endBulkKeyProcess(Object[] aoKey, SimpleOverflowMap.Status[] aStatus) Finish the processing of any number of keys.
protected void	endKeyProcess(Object oKey, SimpleOverflowMap.Status status) Finish the processing of a single key.
protected void	endMapProcess() Release exclusive access for the OverflowMap.
Object	get(Object oKey) Returns the value to which this map maps the specified key.
Map	getBackMap() Returns the back Map.
CacheStatistics	getCacheStatistics() Returns the CacheStatistics for this cache.
protected List	getDeferredList() Obtain the List of keys that may have deferred events.
ObservableMap	getFrontMap() Returns the front Map.
protected MapListener	getFrontMapListener() Get the MapListener for the front map.
Map	getMissCache() Returns the optional miss cache.
protected Map	getStatusMap() Obtain the Map of Status objects for entries managed by this Overflow Map.
protected ThreadGate	getThreadGate() Obtain the ThreadGate for managing key-level and Collection-level operations against the Map, versus Map-level operations themselves.
protected MapListener	instantiateFrontMapListener() Factory pattern: Front Map Listener.
protected SimpleOverflowMap.Status	instantiateStatus() Factory method: Instantiate a Status object.
boolean	isEmpty() Returns true if this map contains no key-value mappings.
boolean	isFrontPutBlind() Determine if the front Map is more efficiently updated using putAll.
boolean	isNullValuesAllowed() Determine if null values are permitted.
protected Iterator	iterateKeys() Create an iterator over the keys in this Map.
protected void	onFrontEvent(MapEvent evt) Either handle an event by turning it over to another thread that is processing the key specified by the event, or take responsibility on this thread for deferring the event and registering its immediate side-effects.
protected void	processDeferredEvents() Process deferred events, if there are any.
protected void	processFrontEvent(SimpleOverflowMap.Status status, MapEvent evt) Process an event.
Object	put(Object oKey, Object oValue) Associates the specified value with the specified key in this map.
void	putAll(Map map) Copies all of the mappings from the specified map to this map.
protected static void	putOne(Map map, Object oKey, Object oValue, boolean fPutBlind) Helper to put a value into a map using either the put or putAll method.
Object	remove(Object oKey) Removes the mapping for this key from this map if present.
protected boolean	removeBlind(Object oKey) Removes the mapping for this key from this map if present.
protected void	setFrontMapListener(MapListener listener) Specify the MapListener for the front map.
void	setFrontPutBlind(boolean fUseFrontPutAll) Specify whether the front Map is more efficiently updated using putAll.
void	setNullValuesAllowed(boolean fAllowNulls) Specify whether null values are permitted.
int	size() Returns the number of key-value mappings in this map.
protected static void	verifyNoNulls(Collection collection, String sAssert) Check the passed collection for nulls, and fail if it contains any.
protected static void	warnEventSequence(MapEvent evtOld, MapEvent evtNew) Issue a one-time warning that events are being received in an order than cannot be explained by normal operation according to the contracts expected by this OverflowMap.

Methods inherited from class com.tangosol.util.AbstractKeyBasedMap

clone, containsValue, entrySet, equals, getAll, hashCode, instantiateEntrySet, instantiateKeySet, instantiateValues, keySet, toString, values

Field Detail

ENTRY_INSERTED

public static final int ENTRY_INSERTED

This event indicates that an entry has been added to the map.

See Also:

Constant Field Values

ENTRY_UPDATED

public static final int ENTRY_UPDATED

This event indicates that an entry has been updated in the map.

See Also:

Constant Field Values

ENTRY_DELETED

public static final int ENTRY_DELETED

This event indicates that an entry has been removed from the map.

See Also:

Constant Field Values

m_mapFront

protected ObservableMap m_mapFront

The "front" map, which is size-limited.

m_mapBack

protected Map m_mapBack

The "back" map, which the front overflows to.

m_mapMiss

protected Map m_mapMiss

The miss cache; may be null.

m_stats

protected SimpleCacheStatistics m_stats

The CacheStatistics object maintained by this cache.

Constructor Detail

SimpleOverflowMap

public SimpleOverflowMap(ObservableMap mapFront,
                         Map mapBack)

Construct a SimpleOverflowMap using two specified maps:

• FrontMap (aka "cache" or "shallow") and
• BackMap (aka "file" or "deep")

Parameters:

mapBack - back map

mapFront - front map

SimpleOverflowMap

public SimpleOverflowMap(ObservableMap mapFront,
                         Map mapBack,
                         Map mapMiss)

Construct a SimpleOverflowMap using three specified maps:

• Front Map (aka "cache" or "shallow") and
• Back Map (aka "file" or "deep")
• Miss Cache

Parameters:

mapFront - front map

mapBack - back map

mapMiss - an optional miss cache

Method Detail

clear

public void clear()

Clear all key/value mappings.

Specified by:

clear in interface Map

Overrides:

clear in class AbstractKeyBasedMap

containsKey

public boolean containsKey(Object oKey)

Returns true if this map contains a mapping for the specified key.

Specified by:

containsKey in interface Map

Overrides:

containsKey in class AbstractKeyBasedMap

Returns:

true if this map contains a mapping for the specified key, false otherwise.

get

public Object get(Object oKey)

Returns the value to which this map maps the specified key.

Specified by:

get in interface Map

Specified by:

get in class AbstractKeyBasedMap

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

isEmpty

public boolean isEmpty()

Returns true if this map contains no key-value mappings.

Specified by:

isEmpty in interface Map

Overrides:

isEmpty in class AbstractKeyBasedMap

Returns:

true if this map contains no key-value mappings

put

public Object put(Object oKey,
                  Object oValue)

Associates the specified value with the specified key in this map.

Specified by:

put in interface Map

Overrides:

put in class AbstractKeyBasedMap

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

putAll

public void putAll(Map map)

Copies all of the mappings from the specified map to this map. The effect of this call is equivalent to that of calling put(java.lang.Object, java.lang.Object) on this map once for each mapping in the passed map. The behavior of this operation is unspecified if the passed map is modified while the operation is in progress.

Specified by:

putAll in interface Map

Overrides:

putAll in class AbstractKeyBasedMap

Parameters:

map - the Map containing the key/value pairings to put into this Map

remove

public Object remove(Object oKey)

Removes 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 Map

Overrides:

remove in class AbstractKeyBasedMap

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()

Returns the number of key-value mappings in this map.

Specified by:

size in interface Map

Overrides:

size in class AbstractKeyBasedMap

Returns:

the number of key-value mappings in this map

iterateKeys

protected Iterator iterateKeys()

Create an iterator over the keys in this Map.

Specified by:

iterateKeys in class AbstractKeyBasedMap

Returns:

a new instance of an Iterator over the keys in this Map

removeBlind

protected boolean removeBlind(Object oKey)

Removes the mapping for this key from this map if present. This method exists to allow sub-classes to optmiize remove functionalitly for situations in which the original value is not required.

Overrides:

removeBlind in class AbstractKeyBasedMap

Parameters:

oKey - key whose mapping is to be removed from the map

Returns:

true iff the Map changed as the result of this operation

getFrontMap

public ObservableMap getFrontMap()

Returns the front Map.

Warning: Direct modifications of the returned map may cause unpredictable behavior of the Overflow Map.

Returns:

the front Map

getBackMap

public Map getBackMap()

Returns the back Map.

Warning: Direct modifications of the returned map may cause unpredictable behavior of the Overflow Map.

Returns:

the back Map

getMissCache

public Map getMissCache()

Returns the optional miss cache.

Warning: Direct modifications of the returned map may cause unpredictable behavior of the Overflow Map.

Returns:

the miss cache, or null if there is no miss cache

getCacheStatistics

public CacheStatistics getCacheStatistics()

Returns the CacheStatistics for this cache.

Returns:

a CacheStatistics object

getThreadGate

protected ThreadGate getThreadGate()

Obtain the ThreadGate for managing key-level and Collection-level operations against the Map, versus Map-level operations themselves.

Returns:

the ThreadGate for the OverflowMap

getStatusMap

protected Map getStatusMap()

Obtain the Map of Status objects for entries managed by this Overflow Map. There will be a Status object for each entry in the front map, and a Status object for each key that has a current operation underway.

Returns:

the Map of Status objects

getDeferredList

protected List getDeferredList()

Obtain the List of keys that may have deferred events.

Returns:

the List of keys of deferred-event Status objects

isNullValuesAllowed

public boolean isNullValuesAllowed()

Determine if null values are permitted. By default, they are not.

Returns:

true iff null values are permitted

setNullValuesAllowed

public void setNullValuesAllowed(boolean fAllowNulls)

Specify whether null values are permitted.

Parameters:

fAllowNulls - pass true to allow null values; false to disallow

isFrontPutBlind

public boolean isFrontPutBlind()

Determine if the front Map is more efficiently updated using putAll. (The use of putAll instead of put is called put-blind because it does not return a value.)

Returns:

true iff the use of the put method should be avoided when updating the front Map, and putAll should be used instead

setFrontPutBlind

public void setFrontPutBlind(boolean fUseFrontPutAll)

Specify whether the front Map is more efficiently updated using putAll.

Parameters:

fUseFrontPutAll - pass true to allow null values; false to disallow

getFrontMapListener

protected MapListener getFrontMapListener()

Get the MapListener for the front map.

Returns:

the MapListener for the front map

setFrontMapListener

protected void setFrontMapListener(MapListener listener)

Specify the MapListener for the front map.

The caller is required to manage all of the thread concurrency issues associated with modifying the listener.

Parameters:

listener - the MapListener for the front map

instantiateFrontMapListener

protected MapListener instantiateFrontMapListener()

Factory pattern: Front Map Listener.

Returns:

a new instance of the listener for the front map

onFrontEvent

protected void onFrontEvent(MapEvent evt)

Either handle an event by turning it over to another thread that is processing the key specified by the event, or take responsibility on this thread for deferring the event and registering its immediate side-effects.

processFrontEvent

protected void processFrontEvent(SimpleOverflowMap.Status status,
                                 MapEvent evt)

Process an event. The Status must already be owned by this thread and in the processing or committing state.

Parameters:

evt - the event to process; may be null

beginKeyProcess

protected SimpleOverflowMap.Status beginKeyProcess(Object oKey)

Block until a key is available for processing, and return the Status object for that key. The caller is then expected to perform its processing, during which time events against the Map Entry may occur. Note that those events can occur on threads other than the current thread; when this current thread can no longer handle events from other threads, it must call SimpleOverflowMap.Status.closeProcessing() and then perform its final adjustments to the Status data structure, handling any events that were queued in the meantime on the Status. After completing the processing during this "quiet period" in which all other threads are prevented from accessing this entry or handling events for this entry, then the caller must call endKeyProcess(java.lang.Object, com.tangosol.net.cache.SimpleOverflowMap.Status) passing the Status object returned from this method.

Parameters:

oKey - the key to process

Returns:

the Status object for the specified key

endKeyProcess

protected void endKeyProcess(Object oKey,
                             SimpleOverflowMap.Status status)

Finish the processing of a single key.

Parameters:

status - the Status object returned from the call to beginKeyProcess(java.lang.Object)

beginBulkKeyProcess

protected SimpleOverflowMap.Status[] beginBulkKeyProcess(Object[] aoKey)

Begin key-level procecessing for any number of keys.

Parameters:

aoKey - an array of zero or more keys; note that this array may be re-ordered by this method

Returns:

an array of Status objects corresponding to the passed keys

See Also:

beginKeyProcess(Object)

endBulkKeyProcess

protected void endBulkKeyProcess(Object[] aoKey,
                                 SimpleOverflowMap.Status[] aStatus)

Finish the processing of any number of keys.

Parameters:

aoKey - the same array of keys as were passed to beginBulkKeyProcess(java.lang.Object[])

aStatus - the array of Status objects returned from the call to beginBulkKeyProcess(java.lang.Object[])

beginMapProcess

protected void beginMapProcess()

Block until this thread has exclusive access to perform operations against the OverflowMap.

endMapProcess

protected void endMapProcess()

Release exclusive access for the OverflowMap.

processDeferredEvents

protected void processDeferredEvents()

Process deferred events, if there are any. This implementation processes only the first deferred event that it encounters.

verifyNoNulls

protected static void verifyNoNulls(Collection collection,
                                    String sAssert)

Check the passed collection for nulls, and fail if it contains any.

Parameters:

collection - a Collection

sAssert - the human-readable description of the error if any nulls are found in the passed Collection

putOne

protected static void putOne(Map map,
                             Object oKey,
                             Object oValue,
                             boolean fPutBlind)

Helper to put a value into a map using either the put or putAll method.

Parameters:

map - the Map to put into

oKey - the key to put

oValue - the value to put

fPutBlind - true to use the putBlind optimization

warnEventSequence

protected static void warnEventSequence(MapEvent evtOld,
                                        MapEvent evtNew)

Issue a one-time warning that events are being received in an order than cannot be explained by normal operation according to the contracts expected by this OverflowMap.

Parameters:

evtOld - the previous (potentially amalgamated) event

evtNew - the new event

instantiateStatus

protected SimpleOverflowMap.Status instantiateStatus()

Factory method: Instantiate a Status object.

Returns:

a new Status object