com.bigdata.resources

Class IndexCache<H extends ILocalBTreeView>

java.lang.Object

com.bigdata.cache.ConcurrentWeakValueCache<K,V>

com.bigdata.cache.ConcurrentWeakValueCacheWithTimeout<NT,H>

com.bigdata.resources.IndexCache<H>

All Implemented Interfaces:

IConcurrentWeakValueCache<NT,H>

public class IndexCache<H extends ILocalBTreeView>
extends ConcurrentWeakValueCacheWithTimeout<NT,H>

Extends the ConcurrentWeakValueCache to track the earliest timestamp from which any local IIndex view is reading. This timestamp is reported by getRetentionTime(). The StoreManager uses this in StoreManager.purgeOldResources() to provide a "read lock" such that resources for in use views are not released.

Version:

$Id$

Author:

Bryan Thompson

Nested Class Summary

Nested classes/interfaces inherited from class com.bigdata.cache.ConcurrentWeakValueCache

ConcurrentWeakValueCache.WeakRef<K,V>

Field Summary

Fields inherited from class com.bigdata.cache.ConcurrentWeakValueCache

DEBUG, INFO, log

Constructor Summary

Constructors

Constructor and Description
IndexCache(int cacheCapacity, long cacheTimeoutMillis)

Method Summary

Methods

Modifier and Type	Method and Description
long	getRetentionTime() The earliest timestamp that MUST be retained for the read-historical indices in the cache and Long.MAX_VALUE if there are NO read-historical indices in the cache.
H	put(NT k, H v) Adds the key-value mapping to the cache.
H	putIfAbsent(NT k, H v) Adds the key-value mapping to the cache iff there is no entry for that key.
protected WeakReference<H>	removeMapEntry(NT k) Overridden to clear the retentionTime if the map entry corresponding to that timestamp is being removed from the map.

Methods inherited from class com.bigdata.cache.ConcurrentWeakValueCache

capacity, clear, containsKey, didUpdate, entryIterator, get, isRemoveClearedReferences, iterator, newWeakRef, remove, removeClearedEntries, size

Methods inherited from class java.lang.Object

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

Constructor Detail

IndexCache

public IndexCache(int cacheCapacity,
          long cacheTimeoutMillis)

Parameters:

cacheCapacity - The capacity of the backing hard reference queue.

cacheTimeoutMillis - The timeout (milliseconds) before an entry which has not been touched is cleared from the cache.

Method Detail

getRetentionTime

public long getRetentionTime()

The earliest timestamp that MUST be retained for the read-historical indices in the cache and Long.MAX_VALUE if there are NO read-historical indices in the cache.

Note: Due to the concurrent operations of the garbage collector, this method MAY return a time that is earlier than necessary. This possibility arises because WeakReference values may be cleared at any time. There is no negative consequence to this behavior - it simply means that fewer resources will be released than might otherwise be possible. This "hole" can not be closed by polling the ReferenceQueue since it is not when the entries are removed from the map which matters, but when their WeakReference values are cleared. However, periodically clearing stale references using #clearStaleRefs() will keep down the size of that "hole".

put

public H put(NT k,
    H v)

Description copied from class: ConcurrentWeakValueCache

Adds the key-value mapping to the cache.

Specified by:

put in interface IConcurrentWeakValueCache<NT,H extends ILocalBTreeView>

Overrides:

put in class ConcurrentWeakValueCache<NT,H extends ILocalBTreeView>

Parameters:

k - The key.

v - The value.

Returns:

The old value under the key -or- null if there is no entry under the key or if the entry under the key has has its reference cleared.

putIfAbsent

public H putIfAbsent(NT k,
            H v)

Description copied from class: ConcurrentWeakValueCache

Adds the key-value mapping to the cache iff there is no entry for that key. Note that a cleared reference under a key is treated in exactly the same manner as if there were no entry under the key (the entry under the key is replaced atomically).

Specified by:

putIfAbsent in interface IConcurrentWeakValueCache<NT,H extends ILocalBTreeView>

Overrides:

putIfAbsent in class ConcurrentWeakValueCache<NT,H extends ILocalBTreeView>

Parameters:

k - The key.

v - The value.

Returns:

the previous value associated with the specified key, or null if there was no mapping for the key or if the entry under the key has has its reference cleared.

removeMapEntry

protected WeakReference<H> removeMapEntry(NT k)

Overridden to clear the retentionTime if the map entry corresponding to that timestamp is being removed from the map.

Overrides:

removeMapEntry in class ConcurrentWeakValueCache<NT,H extends ILocalBTreeView>

Parameters:

k - The key.