Package org.cache2k.core

Class StampedHash<K,V>

java.lang.Object

org.cache2k.core.StampedHash<K,V>

public class StampedHash<K,V>
extends Object

Simple concurrent hash table implementation using optimistic locking via StampedLock for the segments locks.

Author:

Jens Wilke

Constructor Summary

Constructors

Constructor	Description
StampedHash(org.cache2k.Cache<?,?> cache)

Method Summary

Modifier and Type	Method	Description
long	calcEntryCount()	Count the entries in the hash table, by scanning through the hash table.
void	checkExpand(int hash)	Checks whether expansion is needed and expand when insertWithinLock(Entry, int, int) is used.
void	clearWhenLocked()
void	close()	Close the cache by discarding the entry table.
int	getClearOrCloseCount()
Entry<K,V>[]	getEntries()	Entry table used by the iterator.
long	getEntryCapacity()
StampedLock	getSegmentLock(int hash)
long	getSegmentMaxFill()	For testing
long	getSize()	Number of hash table entries.
long	getSizeWithGlobalLock()	Separate version of getSize expected all segments are locked.
Entry<K,V>	insertWithinLock(Entry<K,V> e, int hash, int keyValue)	Insert an entry.
protected boolean	keyObjIsEqual(K key, Entry e)
Entry<K,V>	lookup(K key, int hash, int keyValue)	Lookup the entry in the hash table and return it.
boolean	remove(Entry<K,V> e)	Remove existing entry from the hash.
boolean	removeWithinLock(Entry<K,V> e, int hash)
<T> T	runTotalLocked(Supplier<T> j)	Lock all segments and run the job.
protected int	spreadHashFromEntry(int hc)	Return the spreaded hash code from the hash code that is stored in the entry.

Methods inherited from class java.lang.Object

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

Constructor Detail

StampedHash

public StampedHash(org.cache2k.Cache<?,?> cache)

Parameters:

cache - Cache reference only needed for the cache name in case of an exception

Method Detail

getEntryCapacity

public long getEntryCapacity()

getSegmentMaxFill

public long getSegmentMaxFill()

For testing

lookup

public Entry<K,V> lookup(K key,
                               int hash,
                               int keyValue)

Lookup the entry in the hash table and return it. First tries an optimistic read.

keyObjIsEqual

protected boolean keyObjIsEqual(K key,
                                Entry e)

insertWithinLock

public Entry<K,V> insertWithinLock(Entry<K,V> e,
                                         int hash,
                                         int keyValue)

Insert an entry. Checks if an entry already exists.

checkExpand

public void checkExpand(int hash)

Checks whether expansion is needed and expand when insertWithinLock(Entry, int, int) is used. No lock may be hold when calling this method, since the table must be locked completely using the proper lock order.

Need for expansion is only checked by comparing whether the associated segment is full. Should be called after insert after giving up the lock.

getSegmentLock

public StampedLock getSegmentLock(int hash)

remove

public boolean remove(Entry<K,V> e)

Remove existing entry from the hash.

Returns:

true, if entry was found and removed.

removeWithinLock

public boolean removeWithinLock(Entry<K,V> e,
                                int hash)

spreadHashFromEntry

protected int spreadHashFromEntry(int hc)

Return the spreaded hash code from the hash code that is stored in the entry. For integer keys we store the key directly, so we need to calculate the spread again.

getSize

public long getSize()

Number of hash table entries. Uses locking to read the latest changes and consistent long values for 23 bit systems. May not be called when lock is held.

getSizeWithGlobalLock

public long getSizeWithGlobalLock()

Separate version of getSize expected all segments are locked.

runTotalLocked

public <T> T runTotalLocked(Supplier<T> j)

Lock all segments and run the job.

clearWhenLocked

public void clearWhenLocked()

getClearOrCloseCount

public int getClearOrCloseCount()

close

public void close()

Close the cache by discarding the entry table. Assumes total lock.

Closing will be visible to other threads, because of the guarantees of the locking. Using the entry table for closing has the advantage that the close check collapses with the implicit null check and has no additional overhead.

calcEntryCount

public long calcEntryCount()

Count the entries in the hash table, by scanning through the hash table. This is used for integrity checks.

getEntries

public Entry<K,V>[] getEntries()

Entry table used by the iterator.