Package 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

  • Field Details

    • ENTRY_INSERTED

      public static final int ENTRY_INSERTED
      This event indicates that an entry has been added to the map.
      See Also:

    • ENTRY_UPDATED

      public static final int ENTRY_UPDATED
      This event indicates that an entry has been updated in the map.
      See Also:

    • ENTRY_DELETED

      public static final int ENTRY_DELETED
      This event indicates that an entry has been removed from the map.
      See Also:

    • 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 Details

    • 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:
      mapFront - front map
      mapBack - back 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 Details

    • 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

    • setMissCache

      public void setMissCache(Map mapMiss)
      Set Miss Cache. Note: do not use other than in OverflowScheme#realizeMap(...)
      Parameters:
      mapMiss - miss cache.

    • getCacheStatistics

      public CacheStatistics getCacheStatistics()
      Returns the CacheStatistics for this cache.
      Returns:
      a CacheStatistics object

    • getGate

      protected Gate getGate()
      Obtain the Gate for managing key-level and Collection-level operations against the Map, versus Map-level operations themselves.
      Returns:
      the Gate 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.
      Parameters:
      evt - the event

    • 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:
      status - the status
      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:
      oKey - the key
      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:

    • 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